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Class 12 Notes For Sexual Reproduction in Flowering Plants

Reproduction ensures continuity of species generation after generations as the older individuals undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears complex reproductive units as male and female reproductive units along with accessary structures.

Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen. A typical angiospermic flower consists of four whorls of floral appendages attached on the receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and gynoecium (composed of ovary, style and stigma) .

Pre-fertilisation: Structures and Events

• Several structural and hormonal changes lead to formation and development of the floral primordium. Inflorescence is formed that bears floral buds and then flower.

• In flowers, male (androecium) and female (gynoecium) differentiate and develops in which male and female gametes are produced.

Stamen, Microsporangium and Pollen Grain :

• Stamen consists of long and slender stalk called filament and generally bilobed anthers. Each lobe contains two theca (dithecious).

• The anther is four-sided structure consisting of four microsporangia, two in each lobes.

• Microsporangia develop further and become pollen sacs which contain pollen grains.

• Microsporangium is generally surrounded by four layered walls- the epidermis, endothecium, middle layer and tapetum. Innermost layer tapetum nourishes the developing pollen grains.

• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre of each microsporangium when the anther is young..

Microsporogenesis- The process of the formation and differentiation of microspores (pollen grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.

• The cells of sporogenous tissues undergo meiotic division to form microspore tetrad. As the anther mature and dehydrate, the microspore dissociate and develops into pollen grains.

Pollen grain represents the male gametophytes. Pollen grains are made of 2 layered Wall,

1. Exine :- Made of sporopollenin- most resistant organic matter known.It can withstand high temperatures and strong acids and alkali. No enzyme can degrade sporopollenin

2. Intine :-
-Thin and continuous layer
– Made of cellulose and pectin

3. Germ pores
– apertures on exine where sporopollenin is absent
– forms pollen tube.

4. A plasma membrane surrounds cytoplasm of pollen grain.

MATURE POLLEN
— A mature pollen consist of 2 cells with nucleus (Vegetative and Generative)

VEGETATIVE CELL

• Bigger
• Abundant food reserve
• Large irregular nucleus
• Responsible for the development of pollen grain

GENERATIVE CELL

• Small
• Involves in syngamy (fuse with an egg)
• Dense cytoplasm and nucleus

• Pollen grains of many species e.g Parthenium cause severe allergies and bronchial diseases in some people and leads to chronic respiratory disorders– asthma, bronchitis, etc.

• Pollen grains are rich in nutrients and are used as pollen tablets as food supplements.

• Viability of pollen grain varies with species to species and should land on stigma before this period to germinate. Pollen grains of large number of species are stored in liquid nitrogen at temperature – 196⁰, called pollen bank.

The Pistil, Megasporangium (Ovule) and Embryo sac

• Gynoecium may consists of single pistil (monocarpellary) or more than one pistil (polycarpellary) which may be fused (syncarpous) or free (apocarpous).

e.g Multicarpellary and syncarpous pistil- Papaver

Multicarpellary and apocarpous pistil- Michelia

• Each pistil has three parts the stigma, style and ovary. Inside the ovary is ovarian cavity (locule). The placenta is located inside the ovarian cavity. Megasporangia (ovules) arise from placenta.

Megasporangium (ovule)

• Ovule is a small structure attached to placenta.
• Funicle – stalk by which ovule is attached to placenta
• Hilum- junction between ovule and funicle
• Integuments- protective envelops
• Micropyle- small opening at the tip of ovule into where pollen tube enters
• Chalaza- basal part of ovule
• Nucellus (2n)-mass of cells enclosed in integuments. Has abundant food reserve.

Megasporogenesis- The process of formation of megaspore from megaspore mother cell by meiotic division is known as megasporogenesis. This process takes place in ovule

Ovule differentiates a single megaspore mother cell (MMC) in the micropylar region of nucellus. MMC undergoes meiotic division that results into the production of four megaspores.

• In most of the flowering plants three megaspores degenerate. 1megaspore develops into female gametophyte (embryo sac).

• The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles to form 2-nucleate embryo sac. Two more sequential mitotic division results into 8-nucleate embryo sac.

• Six of the eight nuclei surrounded by cell wall and remaining two nuclei (polar nuclei) are situated below the egg apparatus.

• Three cells are grouped at micropylar end to constitute egg apparatus and three cells at chalazal end forms antipodal cells. At maturity ,embryosac is 8-nucleate and 7 celled.

Pollination – transfer of pollen grains from anther to stigma.

a) Autogamy– transfer of pollen grain from anther to stigma of same flower.

i. Cleistogamous – flower which do not open. cleistogamous flowers are autogamous as there is no chance of cross-pollen landing on the stigma. Cleistogamous flowers produce assured seed-set even in the absence of pollinators. e.g Viola (common pansy), Oxalis, and Commelina.

ii. Chasmogamous– exposed anther and stigma.

b) Geitonogamy – transfer of pollen grains from anther to stigma of different flower of same plant. Geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant

c) Xenogamy– transfer of pollen grain from anther to stigma of different plant’s flower of same species.

Agents of pollination includes abiotic (water, wind) and biotic (insects, butterfly, honey bee etc. large number of pollen grains are produced by plants using abiotic mode of pollination as most of pollen grains are wasted during transfer.

Adaptations in flowers for Pollination

I. Wind Pollination

• pollen grains :– light, non- sticky, winged
• anther :- well exposed
• stigma :- large and feathery
• flower :- one ovule, arranged as inflorescence

Ex : corn cob, cotton, date palm

II. Water Pollination
– Bryophytes, Pteridophytes, Algae

• pollen grains : protected by mucilaginous covering

Ex : Fresh water plants- Vallisneria, Hydrilla
Sea grass- Zostera

Main features of wind and water pollinated plants
– produce pollen grains in large no.
– do not produce nectar

III. Insect Pollination
– Flowers : large, colourful, fragrant, rich in nectar
– Pollen grains : sticky
– Stigma : sticky

Certain rewards to pollinators:

• nectar and (edible) pollen grains as foods
• provide safe place for laying eggs

Ex : Amorphophallus, Yucca

Outbreeding Devices– the various mechanisms take discourage self-pollination and encourage cross pollination as continued self-pollination leads to inbreeding depression. It includes

• Pollen release and stigma receptivity not synchronized.

• Anther and stigma are placed at different position.

• Inhibiting pollen germination in pistil.

• Production of unisexual flowers.

Pollen pistil interaction – the pistil has ability to recognize the compatible pollen to initiate post pollination events that leads to fertilisation. Pollen grain produce pollen tube through germ pores to facilitate transfer of male gametes to embryo sac.

Artificial Hybridization

• Crossing diff varieties of species- hybrid individual- with desirable characters of the parent plants
• desired pollen grains for pollination- stigma protected from contamination
• Emasculation : removal of anther
• Bagging : flower covered- bag made up of butter-prevent contamination of stigma from unwanted pollen

Bagged flower- attains receptivity- mature pollen grains- dusted on the stigma – rebagged- fruits allowed to develop

Double Fertilisation- after entering the one of the synergids, each pollen grain releases two male gametes. One male gametes fuse with egg (Syngamy) and other male gametes fuse with two polar nuclei (triple fusion) to produce triploid primary endosperm nucleus (PEN). Since two types of fusion takes place in an embryo sac the phenomenon is called double fertilisation. The PEN develops into the endosperm and zygote develops into embryo.

Post fertilisation events include endosperm and embryo development, maturation of ovules into seeds and ovary into fruits.

Endosperm– the primary endosperm cell divides many time to forms triploid endosperm tissue having reserve food materials.

Two types of endosperm development :
(i) Free nuclear type (common method)
(ii) Cellular type

(a) Non-albuminous- endosperm completely utilized- before maturation of seeds. e.g pea, groundnut

(b) Albuminous- a portion of endosperm remain in mature seeds. e.g wheat, maize, castor

Embryo- Embryo develops at the micropylar end of the embryo sac where the zygote is located.

Embryogeny – early stages of embryo development.The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.

Embryo consists of:
– embryonal axis
– cotyledons
– plumule
– radicle

Monocotyledonous Seed
– Scutellem = Cotyledon
– Coleorrhiza: undifferentiated sheath covering radical & root cap
– Coleoptile: sheath covering plumule

Seed
– Fertilized and mature ovule develops into seed.

Seed consists of:
– cotyledon(s)
– embryonal axis
– Seed coat- double layered- formed by integuments

• Testa (outer coat)
• Tegmen (inner coat)

– Micropyle:- small opening on seed coat, it facilitates entry of H2O & O2 into seeds (for germination)
– Hilum:- scar on seed coat
– Seed – Albuminous / Non-Albuminous
– Perisperm : remnants of nucellus that is persistent. Ex: Black pepper
– Dormancy: state of inactivity

• The wall of ovary develops into wall of fruit called pericarp. In true fruits only ovary contributes in fruit formation by in false fruit thalamus also contributes in fruit formation.

Apomixis
– Form of asexual reproduction- mimics sexual reproduction- seed formed without fertilisation
– Formation of apomictic seeds :
• diploid cell (formed without meiosis)- develop into embryo without fertilization
• cells of nucellus (2n) surrounding embryo sac- protrude into embryo sac- develop into embryos. Ex. Citrus and Mango.

Polyembryony
– Occurrence of more than one embryo in a seed
– Often associated with apomixes. Ex: Citrus, groundnut     

Class 12 Biology Revision Notes

Reproduction is a biological process of formation of new offsprings from the pre-existing organism. Reproduction becomes a vital process without which species cannot survive for long It ensures continuity of species generation after generations as older individuals undergo senescence and ultimately they die.

Life span – • The period from birth to the natural death of an organism represents its life span. Life span of organisms varies from few days (Butterfly-1to 2 weeks) to thousands of years (Banyan tree).

Types of Reproduction:
Based on whether there is one or two organisms taking part in the process of reproduction

• ASEXUAL REPRODUCTION
• SEXUAL REPRODUCTION

When the offspring is produced by single parents with or without the involvement of gamete formation, the reproduction is called asexual reproduction.

When two parents (opposite sex) participates in reproduction process and also involves the fusion of male and female gametes, it is called sexual reproduction.

Asexual Reproduction

1. Usually followed by organisms with relatively simpler organizations.
2. Offsprings produced by single parent.
3. With/without involvement of gamete formation.
4. Offsprings produced are genetically and morphologically similar to each other and to the parent, i.e. they are clones.

• In Protista and Monera, the parent cells divides into two to give rise to new individuals. Thus, in these organisms cell division is the mode of reproduction itself.

• Binary fission– in this method of asexual reproduction, a cell divides into two halves and rapidly grows into an adult. Ex- amoeba, paramecium.

• Budding– small buds are produced that remain attached initially with parents and get separated on maturation. Ex. Yeast.

• Fungi and simple plants like algae reproduce through special reproductive structures like zoospores (motile structure), conidia (penicillium), buds (hydra) and gemmules (sponges).

• In plants, vegetative reproduction occurs by vegetative propagules like runner, rhizome, sucker, tuber, offset and bulb.

WATER HYACINTH (Terror of Bengal)

• One of the most invasive weeds
• Grows wherever there is standing water
• Drains oxygen from water- leads to death of fishes.
• Introduced in India because of its pretty flowers & shape of leaves
• Vegetative propagation occurs at a phenomenal rate

Asexual reproduction is the most common method of reproduction in organisms having simpler body like in algae and fungi but during unfavorable condition they shift to sexual reproduction.

SEXUAL REPRODUCTION:

• Involves formation of male and female gamete by two individuals of the opposite sex.
• Offspring produced by fusion of male and female gametes not identical to each other or to the parents.
• All sexually reproducing organisms share a similar pattern of reproduction.

• In sexual reproduction, fusion of male and female gametes results in offspring that are not identical to parents.

DIFFERENT PHASES IN SEXUAL REPRODUCTION:

a. Juvenile phase – The period between birth and sexual maturity is called juvenile phase. In plants it is known as vegetative phase.The end of juvenile/vegetative phase marks the beginning of the reproductive phase.

b. Reproductive phase-

• Some plants show flowering in particular season and some other flowers in all seasons. Some other plants like bamboo species flowers once in life time (after 50-100 years), Strobilanthus kunthiana (neelakuranji),flowers once in 12 years.

• The female placental animals exhibit cyclic change in activities ovaries and accessary glands as well as hormone during the reproductive phase.

Menstrual cycle
• It occurs in monkeys, apes and human beings.
• Cycle consists of 3 phases-menstrual, proliferative and secretory phase.
• Blood flows in the last few days of the cycle. The broken endometrium is passed out during menstruation.
• Female does not permit copulation during menstrual phase of the cycle.

Oestrous cycle
• It occurs in non primates like cow, sheep, rat, deer, dog, tiger etc.
• It consists of a short period of oestrous or heat. it is 12-24 hours in cow followed by anoestrous or passive period.
• Blood does not flow in this cycle. The broken endometrium is reabsorbed.
• Female permits copulation only during oestrous period.
• Both in plants and animals, hormones are responsible for the transition between different phases of life cycle. Interaction between hormones and environmental factors regulate the reproductive processes.

c. Senescent phase –

• It is the end of reproductive phase.
• Old age ultimately leads to death

Events in Sexual Reproduction : Pre-fertilisation, Fertilisation, Post-fertilisation

Pre-fertilisation– all the events prior to fusion of gametes are included in it. It includes gametogenesis and gamete transfer.

a. Gametogenesis is the process of formation of male and female gametes. Gametes are haploid cells which may be similar or dissimilar in structure. In algae, both gametes are similar in structure called homogametes (isogametes). In higher organism that reproduces sexually, two morphologically distinct gametes are formed called heterogametes, male gametes are called antherozoid or sperm and female gametes are called ovum or egg.

Isogametes. heterogametes

In fungi and plants, homothallic and monoecious terms are used to denote the bisexual condition and heterothallic and dioecious are used for unisexual condition. In flowering plants, the unisexual male flower is staminate, i.e., bearing stamens, while the female is pistillate or bearing pistils.

• In animals, species which possess both male and female reproductive organs in same individual are called bisexual or hermaphrodites (earthworm, sponges, tapeworm etc.) and both having either male or female reproductive organs are called unisexual (cockroach, human).

• Gametes are always haploid( having half set of chromosome ), although organisms may be haploid and diploid. Diploid organisms form gametes by meiotic division. The organisms belonging to algae, fungi, and bryophytes have haploid plant body and pteridophytes, gymnosperms, angiosperms and most of animals are diploid ( having double set of chromosome )

• In diploid organisms, gamete mother cell (meiocyte) undergoes meiosis in which one set of chromosome is present in gametes.

b. Gamete Transfer – in majority of organisms, male gametes are motile and females gametes are non-motile, except in fungi and algae in which both gametes are motile.

• In simple plants like algae, fungi, bryophytes and pteridophytes water is the medium through which male and female gametes moves. The number of male gametes are much more than number of female gametes as most of male gametes fail to reach the female gametes.

• In higher plants pollen grains are carrier of male gametes and ovule has eggs. Pollen grains must be transferred from anther to stigma to facilitate fertilisation. The transfer of pollen grains from anther to stigma is called pollination. Pollination may be self (anther to stigma of same flower) or cross (anther to stigma of different flower).

• Pollen grains germinate on stigma to produce pollen tube that delivers the male gametes near the ovule.

c. Fertilisation – The fusion of male and female gamete is called fertilization or syngamy. It results in the formation of diploid zygote.

• The process of development of new organisms without fertilisation of female gametes is called parthenogenesis. For example honey bee, rotifers, and lizards

EXTERNAL FERTILIZATION	INTERNAL FERTILIZATION
Syngamy occurs outside the body of the organism Large numbers of gametes are released in the surrounding medium. Ex. Bony fishes and Amphibians.	Syngamy occurs inside the body of the organism Numbers of ova produced are less, but large numbers of male gametes are released and they travel towards the ovum. Ex. Birds and Mammals.

d. Post Fertilisation Events- events in the sexual reproduction after formation of zygote.

Zygote is the vital link that ensures continuity of species between organisms of one generation and the next. Every sexually reproducing organism, including human beings, begin life as a single cell–the zygote.

• In the organisms, having external fertilisation, zygote is formed in external medium (water) and those having internal fertilisation zygote is formed inside the body of female.

• In algae and fungi, zygote develops a thick wall resistant to desiccation and damage. This germinates after a period of rest.

• In the organisms having haplontic life cycle, zygote divides to form haploid spores that germinate to form haploid individual.

Embryogenesis – the process of development of embryo from the zygote. During this, zygote undergoes mitotic division and cell differentiation. Cell division increase the number and cell differentiation help information of new group of cells and organs.

Oviparous	Viviparous
Development of zygote takes place outside the body of organisms and lay fertilized of unfertilized eggs.Ex – Reptiles and birds.	Development of zygote takes place inside the body of organisms and produces young ones.Ex- Human, dog, horse etc.

• In flowering plants, zygote is formed inside the ovule. After fertilisation, sepals, petals and stamens of flower fall off. The zygote develops into embryo and ovules into seeds. The ovary develops into fruits which develop a thick wall called pericarp, protective in function.

• After dispersal, seeds germinate under favorable condition to produce new plants.

A few kinds of fruit showing seeds (S) and protective pericarp (P)      

Class 12 Chemistry Revision Notes Chapter 16 Chemistry in Everyday Life

• Drugs:  Drugs are low molecular mass substances which interact with targets in the body and produce a biological response.
• Medicines: Medicines are chemicals that are useful in the diagnosis, prevention, and treatment of diseases
• Therapeutic effect: Desirable or beneficial effect of a drug like the treatment of symptoms and cure of a disease on a living body is known as therapeutic effect
• Enzymes: Proteins which perform the role of biological catalysts in the body are called enzymes
• Functions of enzymes:
  (i) The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of enzymes hold the substrate molecule in a suitable position so that it can be attacked by the reagent effectively.
  (ii) The second function of an enzyme is to provide functional groups that will attack the substrate and carry out chemical reaction.
• Role of drugs: Main role of drugs is to either increase or decrease role of enzyme catalysed reactions. Inhibition of enzymes is a common role of drug action.
• Enzyme inhibitor: Enzyme inhibitor is drug which inhibits catalytic activity of enzymes or blocks the binding site of the enzyme and eventually prevents the binding of substrate with enzyme.
• Drug can inhibit attachment of substrate on active site of enzymes in following ways:
  

1. Competitive Inhibition: Competitive Inhibitors are the drugs that compete with the natural substrate for their attachment on the active sites of enzymes.
2. Non-Competitive Inhibition: Some drugs do not bind to the enzyme’s active site, instead bind to a different site of enzyme called allosteric site. This binding of inhibitor at allosteric site changes the shape of the active site in such a way that substrate cannot recognise it. If the bond formed between an enzyme and an inhibitor is a strong covalent bond and cannot be broken easily, then the enzyme is blocked permanently. The body then degrades the enzyme-inhibitor complex and synthesizes the new enzyme.
   

• Receptors: Proteins which are vital for communication system in the body are called receptors. Receptors show selectivity for one chemical messenger over the other because their binding sites have different shape, structure, and amino acid composition.
• Receptors as Drug Targets: In the body, message between two neurons and that between neurons to muscles is communicated through chemical messengers. They are received at the binding sites of receptor proteins. To accommodate a messenger, shape of the receptor site changes which brings about the transfer of message into the cell. Chemical messenger gives message to the cell without entering the cell. 
• Antagonists and Agonists: Drugs that bind to the receptor site and inhibit its natural function are called antagonists. These are useful when blocking of message is required. Drugs that mimic the natural messenger by switching on the receptor are called agonists. These are useful when there is lack of natural chemical messenger.
• Therapeutic action of different classes of drugs:
  (i) Antacid: Chemical substances which neutralize excess acid in the gastric juices and give relief from acid indigestion, acidity, heart burns and gastric ulcers. Examples: Eno, gelusil, digene etc.
  (ii) Antihistamines: Chemical substances which diminish or abolish the effects of histamine released in body and hence prevent allergic reactions. Examples: Brompheniramine (Dimetapp) and terfenadine (Seldane).
  (iii) Neurologically Active Drugs: Drugs which have a neurological effect i.e. affects the message transfer mechanism from nerve to receptor.
• Tranquilizers: Chemical substances used for the treatment of stress and mild or severe mental diseases. Examples: Derivatives of barbituric acids like veronal, amytal, Nembutal, luminal, seconal.
• Analgesics: Chemical substances used to relieve pain without causing any disturbances in the nervous system like impairment of consciousness, mental confusion, in coordination or paralysis etc.
• Classification of Analgesics:
  (a) Non-narcotic analgesics: They are non-addictive drugs. Examples: Aspirin, Ibuprofen, Naproxen, Dichlofenac Sodium.
  (b) Narcotic analgesics: When administered in medicinal doses, these drugs relieve pain and produce sleep. Examples: Morphine and its derivatives) Anti-microbials: Drugs that tends to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (anti-fungal agents), virus (antiviral agents), or other parasites (anti-parasitic drugs) selectively.
  v) Anti-fertility Drugs: Chemical substances used to prevent conception or fertilization are called anti-fertility drugs. Examples – Norethindrone, ethynylestradiol (novestrol).
• Types of antimicrobial drugs :
  (a) Antibiotics: Chemical substances produced by microorganisms that kill or prevent the growth of other microbes.

Classification of antimicrobial drugs based on the mode of control of microbial diseases:

1. Bactericidal drugs – Drugs that kills organisms in the body. Examples – Penicillin, Aminoglycosides, Ofloxacin.
2. Bacteriostatic drugs – Drugs that inhibits growth of organisms. Examples – Erythromycin, Tetracycline, Chloramphenicol.

Classification of antimicrobial drugs based on its spectrum of action:

1. Broad-spectrum antibiotics – Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are called broad-spectrum antibiotics. Examples – Ampicillin and Amoxycillin.
2. Narrow spectrum antibiotics – Antibiotics which are effective mainly against Gram-positive or Gram-negative bacteria are called narrow-spectrum antibiotics. Examples- Penicillin G.
3. Limited spectrum antibiotics  -Antibiotics effective against a single organism or disease

(b) Antiseptics: Chemical substances that kill or prevent growth of microorganisms and can be applied on living tissues such as cuts, wounds etc., are called anti-spetics. Examples – Soframicine, dettoletc.

(c) Disinfectants: Chemical substances that kill microorganisms but cannot be applied on living tissues such as cuts, wounds etc., are called disinfectants. Examples – Chlorine (Cl2), bithional, iodoform etc.

• Food additives: Food additives are the substances added to food to preserve its flavor or improve its taste and appearance.
• Different types of food additives:

1. Artificial Sweetening Agents: Chemical compounds which gives sweetening effect to the food and enhance its flavour. Examples – Aspartame, Sucrolose and Alitame.
2. Food preservatives: Chemical substances which are added to food material to prevent their spoilage due to microbial growth. Examples – Sugar, Salts, Sodium benzoate
3. Food colours: Substances added to food to increase the acceptability and attractiveness of the food product. Examples – Allura Red AC, Tartrazine
4. Nutritional supplements: Substances added to food to improve the nutritional value. Examples -Vitamins, minerals etc.
5. Fat emulsifiers and stabilizing agents: Substances added to food products to give texture and desired consistency. Examples – Egg yolk (where the main emulsifying chemical is Lecithin)
6. Antioxidants: Substances added to food to prevent oxidation of food materials. Examples – ButylatedHydroxy Toluene (BHT), ButylatedHydroxy Anisole (BHA).

• Soaps: It is a sodium or potassium salts of long chain fatty acids like stearic, oleic and palmitic acid.

This reaction is known as saponification.

• Types of soaps:

1. Toilet soaps are prepared by using better grades of fats and oil sand care is taken to remove excess alkali. Colour and perfumes are added to make these more attractive.
2. Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent.
3. In medicated soaps, substances of medicinal value are added. In some soaps, deodorants are added.
4. Shaving soaps contain glycerol to prevent rapid drying. A gum called, rosin is added while making them. It forms sodium rosinate which lathers well.
5. Laundry soaps contain fillers like sodium rosinate, sodium silicate, borax, and sodium carbonate.
6. Soaps that float in water are made by beating tiny air bubbles before their hardening.
7. Soap chips are made by running a thin sheet of melted soap ontoa cool cylinder and scraping off the soaps in small broken pieces.
8. Soap granules are dried miniature soap bubbles.
9. Soap powders and scouring soaps contain some soap, a scouring agent (abrasive) such as powdered pumice or finely divided sand, and builders like sodium carbonate and trisodium phosphate.

• Advantages of using soaps: Soap is a good cleansing agent and is 100% biodegradable i.e. micro- organisms present in sewage water can completely oxidize soap. Therefore, soaps do not cause any pollution problems.
• Disadvantages of using soaps: Soaps cannot be used in hard water because hard water contains metal ions like Ca2+ and Mg2+ which react with soap to form a white precipitate of calcium and magnesium salts

These precipitates stick to the fibers of the cloth as gummy mass and block the ability of soaps to remove oil and grease from fabrics. Therefore, it interferes with the cleansing ability of the soap and makes the cleansing process difficult.

In acidic medium, the acid present in solution precipitate the insoluble free fatty acids which adhere to the fabrics and hence block the ability of soaps to remove oil and grease from the fabrics. Hence soaps cannot be used in acidic medium

• Detergents: Detergents are sodium salts of long chain of alkyl benzene sulphonic acids or sodium salts of long chain of alkyl hydrogen sulphates.

• Classification of detergents:

(a)Anionic detergents: Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl hydrogen sulphates formed by treating long chain alcohols with concentrated sulphuric acid are neutralised with alkali to form anionic detergents. Similarly alkyl benzene sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali. Anionic detergents are termed so because a large part of molecule is an anion.

They are used in household cleaning like dishwasher liquids, laundry liquid detergents, laundry powdered detergents etc. They are effective in slightly acidic solutions where soaps do not work efficiently.

(b)Cationic detergents: Cationic detergents are quarternary ammonium salts of mine with acetates, chlorides or bromides as anions. Cationic parts possess a long hydrocarbon chain and a positive charge on nitrogen atom. Cationic detergents are termed so because a large part of molecule is a cation. Since they possess germicidal properties, they are used as germicides. They has strong germicidal action, but are expensive.

(c) Non- ionic detergents: They do not contain any ion in their constitution. They are like esters of high molecular mass.

Example: Detergent formed by condensation reaction between stearic acid reacts and poly ethyl eneglycol.

It is used in Making liquid washing detergents. They have effective H- bonding groups at one end of the alkyl chain which make them freely water soluble.

• Biodegradable detergents: Detergents having straight hydrocarbon chains that are easily decomposed by microorganisms. Example: Sodium lauryl sulphate

• Non-Biodegradable detergents: Detergents having branched hydrocarbon chains that are not easily decomposed by microorganisms.

Class 12 Chemistry Revision Notes Chapter 15 Polymers

• Polymers: Polymers are high molecular mass substance consisting of large number of repeating structural units. As polymers are single, giant molecules i.e. big size molecules, they are also called macromolecules
• Monomers: The simple molecules which combine to form polymers by forming single or multiple bonds are called monomers.
• Polymerization: The process of formation of polymers from respective monomers is called polymerization
• Classification of Polymers:

1. Based on source of availability, it is classified into
   1. Natural polymers: Polymers obtained from nature, mostly plants and animals. Examples – Cellulose, starch, etc.
   2. Synthetic polymers: Polymers prepared in laboratory. Examples – Teflon, Nylon 6,6 , Synthetic rubber (Buna – S) etc.
   3. Semi synthetic polymers: Polymers derived from naturally occurring polymers by carrying out chemical modifications. Examples – Rayon (cellulose acetate), cellulose nitrate, etc.
2. Based on the structure of polymer, it is classified into
   1. Linear polymers: Polymer consists of long and straight chains. Examples – High density polythene, polyvinyl chloride, etc.
   2. Branched chain polymers: Polymers contains linear chains having some branches. Examples – Low density polythene
   3. Cross linked or network polymers: Polymers in which monomer units are cross linked together to form a 3 dimensional network polymers. Examples – Bakelite, melamine, etc.
3. Based on the mode of polymerisation, it is classified into
   I. Addition polymers: Polymers are formed by the repeated addition of monomers with double and triple bonds. It is further classified into,
   Homopolymers:Polymers formed by the polymerisation of a single monomeric species. Examples – Polythene, Polystyrene.
   Copolymers:Polymers formed by addition polymerisation of two different monomers. Examples – Buna-S, Buna –N.
   II. Condensation polymers: Polymers formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric units with elimination of simple molecules. Examples – Nylon 6, 6, Nylon 6.

Based on Molecular forces, it is classified into

Step 1: Chain initiating step: Organic peroxides undergo homolytic fission to form free radicals which acts as initiator. Initiator adds to C-C double bond of an alkene molecule to form a new free radical

Step 2: Chain propagating step: Free radicals formed by homolytic cleavage adds to a double bond of monomer to form a larger free radical. Radical formed adds to another alkene molecule to form a larger free radical. This process continues until the radical is destroyed. These steps are called propagation steps.

Step 3: Chain terminating step: For termination of the long chain, free radicals combine in different ways to form polythene. One mode of termination of chain is shown as under:

a). Low density polythene (LDP) is a polymer of ethene.

It is used in the insulation of electricity carrying wires and manufacture of squeeze bottles, toys and flexible pipes

b). High density polythene(HDP) is a polymer of ethene.

It is used for manufacturing buckets, dustbins, bottles, pipes, etc.

c). Polytetrafluoroethene (is a polymer of Teflon)

It is used in making oil seals and gaskets and also used for non – stick surface coated utensils

d). Polyacrylonitrile is a polymer of acrylonitrile.

It is used as a substitute for wool in making commercial fibres such as orlon or acrilan.

1. Polyamides: Polymers possess amide linkage (-CONH-) in chain. Thesepolymers are popularly known as nylons. Examples:
(a) Nylon 6, 6: It is prepared by the condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature. 
It is used in making sheets, bristles for brushes and in textile industry.

(b) Nylon 6: It is obtained by heating caprolactum with water at a high temperature 
It is used for the manufacture of tyre cords, fabrics and ropes.

2. Polyesters: These are the polycondensation products of dicarboxylic acids and diols Example: Terylene or Dacron

It is used to create resistance in polymerised product and is used in blending with cotton and wool fibres and also as glass reinforcing materials in safety helmets, etc.

3. Phenol – formaldehyde polymer (Bakelite and related polymers)

a). Bakelite: These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The initial product could be a linear product – Novolac used in paints.

b). Novolac on heating with formaldehyde forms Bakelite

It is used for making combs, phonograph records, electrical switches and handles of various utensils

4. Melamine – formaldehyde polymer: Melamine formaldehyde polymer isformed by the condensation polymerisation of melamine and formaldehyde

It is used in the manufacture of unbreakable crockery.

a). Natural rubber: Natural rubber is a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis – 1, 4 – polyisoprene.

b). Synthetic rubber: Synthetic rubbers are either homopolymers of 1, 3 – butadiene derivatives or copolymers of 1, 3 – butadiene or its derivatives with another unsaturated monomer.

A) Neoprene or polychloroprene

It is used for manufacturing conveyor belts, gaskets and hoses

B) Buna – N

It is used in making oil seals, tank lining, etc. because it is resistant to the action of petrol, lubricating oil and organic solvents

C) Buna – S

a). Poly – -hydroxybutyrate – co--hydroxyvalerate (PHBV):
It is obtained by the copolymerisation of 3-hydroxybutanoic acid and 3 – hydroxypentanoic acid

It is used in speciality packaging, orthopaedic devices and in controlled release of drugs.

b). Nylon 2–nylon 6: It is an alternating polyamide copolymer of glycine(H2N–CH2–COOH) and amino caproic acid (H2N (CH2)5 COOH)

Name of Polymer	Monomer	Structure	Uses
Polypropene	Propene		Manufacture of ropes, toys, pipes, fibres, etc.
Glyptal	(a) Ethylene glycol Manufacture of(b) Phthalic acid		Manufacture of paints and lacquers
Polystyrene	Styrene		As insulator, wrapping material, manufacture of toys, radio and television cabinets
Polyvinyl chloride (PVC)	Vinyl chloride		Manufacture of rain coats, hand bags, vinyl flooring, water pipes

1. Elastomers: Polymer chains are held together by weakest intermolecular forces. Polymers are rubber – like solids with elastic properties. Examples – Buna – S, Buna – N, Neoprene.
2. Fibre: Polymers have strong intermolecular force like hydrogen bonding. Fibres are the thread forming solids which possess high tensile strength and high modulus. Examples – Nylon 6, 6, Polyesters.
3. Thermoplastic polymers: Polymers are held by intermolecular forces which are in between those of elastomers and fibres. These polymers are capable of repeated softening on heating and hardening on cooling. Examples – Polythene, Polystyrene.
4. Thermosetting polymers: Polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and eventually undergo a permanent change. Examples – Bakelite, Urea-formaldelyde resins
5. Addition Polymerisation or Chain Growth Polymerisation: Addition polymerisation is called chain growth polymerisation because it takes place through stages leading to increase in chain length and each stage produces reactive intermediates for use in next stage of the growth of chain. Most common mechanism for addition polymerisation reactions is free radical mechanism

Important Addition Polymers:

Condensation Polymerisation or Step Growth polymerization: Polymerisation generally involves a repetitive condensation reaction between two bi-functional monomers. In condensation reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Since, each step produces a distinct functionalized species and is independent of each other, this process is also called as step growth polymerisation.

Condensation Polymers:

Terylene or Dacron: It is manufactured by heating a mixture of ethylene glycol and terephthalic acid at 420 to 460 K in the presence of zinc acetate-antimony trioxide catalyst.

Vulcanisation of rubber: The process of heating a mixture of raw rubber with sulphur and an appropriate additive in a temperature range between 373 K to 415 K to improve upon physical properties like elasticity, strength etc.

Examples of synthetic rubber:

Biodegradable Polymers: Polymers which are degraded by microorganisms within a suitable period so that biodegradable polymers and their degraded products do not cause any serious effects on environment.

Examples of biodegradable polymer:

Commercially important polymers along with their structures and uses

Class 12 Quick Revision Notes for Chapter 14 Biomolecules Chemistry

• Carbohydrates: Polyhydroxy aldehydes or polyhydroxy ketones or compounds on hydrolysis give carbohydrates.
• Classification of carbohydrates:
  Monosaccharides
  (a) Simplest carbohydrates
  (b) It cannot be hydrolysed into simpler compounds
  (c) Examples – Glucose, mannose
  Oligosaccharides
  (a) Carbohydrates which gives 2 to 10 monosaccharide units on hydrolysis
  (b) Examples – Sucrose, Lactose, Maltose
  Polysaccharides
  (a) Carbohydrates which on hydrolysis give large number of monosaccharide units.
  (b) Examples – Cellulose, starch
• Anomers: Pair of optical isomers which differ in configuration only around C1 atom are called anomers. Examples – -D-glucopyranose and -D-glucopyranose.
• Epimers: Pair of optical isomers which differ in configuration around any other C atom other than C1 atom are called epimers. E.g. D-glucose and D- mannose are C2epimers.
  

Preparation of glucose (also called dextrose, grape sugar):

• From starch

• Structure of glucose

• Structure elucidation of glucose:

a) D – glucose with HI

b) D – glucose with HCN

c) D – glucose with NH₂OH

d) D- glucose with Fehling’s reagent

e) D – glucose with Tollen’s reagent

f) D – glucose with nitric acid

g) D – glucose with (CH₃CO)₂O and ZnCl₂

h) D – glucose with bromine water

i) Glucose with phenylhydrazine to form osazone

Glucose and fructose gives the same osazone because the reaction takes place at C1 and C2 only.

• Other Reactions of Glucose (Presence of ring structure)

Glucose does not give Schiff’s test and does not react with sodium bisulphite and NH3. Pentaacetyl glucose does not react with hydroxyl amine. This shows the absence of –CHO group and hence the presence of ring structure.

• Cyclic structure of glucose:

• Haworth representation of glucose:

• Cyclic structure of fructose:

• Haworth representation of fructose

• Glycosidic linkage: The oxide linkage formed by the loss of a water molecule when two monosaccharides are joined together through oxygen atom is called glycosidic linkage.
• Sucrose (invert sugar):

a) Sucrose is a non-reducing sugar because the two monosaccharide units are held together by a glycosidic linkage between C1 of -glucose and C2 of – fructose. Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non-reducing sugar.

b) Sucrose is dextrorotatory but on hydrolysis it gives dextrorotatory & laevorotatory and the mixture is laevorotatory.

• Haworth Projection of Sucrose:

• Maltose:

1. Maltose is composed of two α-D-glucose units in which C1 of one glucose (I) is linked to C4 of another glucose unit (II).
2. The free aldehyde group can be produced at C1 of second glucose in solution and it shows reducing properties so it is a reducing sugar.
   

• Haworth projection of maltose:
  
• Lactose (Milk sugar):It is composed of β-D-galactose and β-D-glucose. The linkage is between C1 of galactose and C4 of glucose. Hence it is also a reducing sugar.
  
• Haworth projection of lactose:

• Starch: It is a polymer of -glucose and consists of two components — Amylose and Amylopectin.
• Amylose:

1. It is a water soluble component
2. It is a long unbranched chain polymer
3. It contains 200 – 1000 -D-(+)- glucose units held by – glycosidic linkages involving C1 – C4glycosidic linkage
4. It constitutes about 15-20% of starch

• Amylopectin

1. It is a water insoluble component
2. It is branched chain polymer
3. It forms chain by C1 – C4glycosidic linkage whereas branching occurs by C1 – C6glycosidic linkage
4. It constitutes about 80-85% of starch

• Cellulose:

1. It occurs exclusively in plants.
2. It is a straight chain polysaccharide composed only of -D-glucose units which are joined by glycosidic linkage between C1 of one glucose unit and C4 of the next glucose unit.

• Glycogen:

1. The carbohydrates are stored in animal body as glycogen.
2. It is also known as animal starch because its structure is similar to Amylopectin.
3. It is present in liver, muscles and brain.
4. When the body needs glucose, enzymes break the glycogen down to glucose.

• Amino acids:

Amino acids contain amino (–NH2) and carboxyl (–COOH) functional groups.

Where R – Any side chain
Most naturally occurring amino acids have L – Config.

• Types of amino acids:

a). Essential amino acids: The amino acids which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids. Examples: Valine, Leucine

b). Non-essential amino acids: The amino acids, which can be synthesised in the body, are known as non-essential amino acids. Examples: Glycine, Alanine

• Zwitterion form of amino acids:

1. Amino acids behave like salts rather than simple amines or carboxylic acids. This behaviour is due to the presence of both acidic (carboxyl group) and basic (amino group) groups in the same molecule. In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion known as zwitter ion. This is neutral but contains both positive and negative charges.
2. In zwitterionic form, amino acids show amphoteric behaviour as they react both with acids and bases.

• Isoelectronic point: The pH at which the dipolar ion exists as neutral ion and does not migrate to either electrode cathode or anode is called isoelectronic point.
• Proteins: Proteins are the polymers of -amino acids and they are connected to each other by peptide bond or peptide linkage. A polypeptide with more than hundred amino acid residues, having molecular mass higher than 10,000u is called a protein.
• Peptide linkage: Peptide linkage is an amide linkage formed by condensation reaction between –COOH group of one amino acid and –NH2 group of another amino acid.

Peptide link age

• Primary structure of proteins: The sequence of amino acids is said to be the primary structure of a protein.
• Secondary structure of proteins: It refers to the shape in which long polypeptide chain can exist. Two different types of structures:

– Helix:

1. It was given by Linus Pauling in 1951
2. It exists when R- group is large.
3. Right handed screw with the NH group of each amino acid residue H – bonded to – C = O of adjacent turn of the helix.
4. Also known as 3.613 helix since each turn of the helix hasapproximately 3.6 amino acids and a 13 – membered ring is formed by H – bonding.
5. C = O and N – H group of the peptide bonds are trans to each other.
6. Ramchandran angles (and) – angle which makes with N – H and angle which makes with C = O.

– pleated sheet:

1. It exists when R group is small.
2. In this conformation, all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by hydrogen bonds.

• Tertiary structure of proteins: It represents the overall folding of the polypeptide chain i.e., further folding of the 2° structure.
• Types of bonding which stabilize the 3° structure:

1. Disulphide bridge (-S – S-)
2. H – bonding – (C = O … H – N)
3. Salt bridge (COO– … + )
4. Hydrophobic interactions
5. van der Waals forces

• Two shapes of proteins:

Fibrous proteins
a) When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre– like structure is formed.
b) These proteins are generally insoluble in water
c) Examples: keratin (present in hair, wool, silk) and myosin (present in muscles), etc

Globular proteins
a) This structure results when the chains of polypeptides coil around to give a spherical shape.
b) These are usually soluble in water.
c) Examples: Insulin and albumins

• Quaternary structure of proteins:

1. Some of the proteins are composedof two or more polypeptide chains referred to as sub-units.
2. The spatial arrangement of these subunits with respect to each other is known as quaternary structure of proteins.

• Denaturation of proteins:

1. The loss of biological activity of proteins when a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH. This is called denaturation of protein.
2. Example: coagulation of egg white on boiling, curdling of milk.

• Nucleoside:

1. Base + sugar

• Nucleotide:

1. Base + sugar + phosphate group

• Nucleic acids (or polynucletides):

1. Long chain polymers ofnucleotides.
2. Nucleotides are joined by phosphodiester linkage between 5’ and 3’ C atoms of a pentose sugar.

• Two types of nucleic acids:DNA

1. It has a double stranded -helix structure in which two strands are coiled spirally in opposite directions.
2. Sugar present is –D–2-deoxyribose
3. Bases:
   i) Purine bases: Adenine (A) and Guanine (G)
   ii) Pyrimidine bases: Thymine (T) and cytosine (C)
4. It occurs mainly in the nucleus of the cell.
5. It is responsible for transmission for heredity character.RNA

1. It has a single stranded -helix structure.
2. Sugar present is –D–ribose
3. Bases:
   i) Purine bases: Adenine (A) and Guanine (G)
   ii) Pyrimidine bases: Uracil (U) and cytosine (C)
4. It occurs mainly in the cytoplasm of the cell.
5. It helps in protein synthesis.

Double helix structure of DNA:

1. It is composed of two right handed helical polynucleotide chains coiled spirally in opposite directions around the same central axis.
2. Two strands are anti-parallel i.e., their phosphodiester linkage runs in opposite directions.
3. Bases are stacked inside the helix in planes to the helical axis.
4. Two strands are held together by H – bonds (A = T, G C).
5. The two strands are complementary to each other because the hydrogen bonds are formed between specific pairs of bases.
6. Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds with guanine.
7. Diameter of double helix is 2 nm.
8. Double helix repeats at intervals of 3.4 nm. (One complete turn)
9. Total amount of purine (A + G) = Total amount of pyramidine (C + T)

• Vitamins: Vitamins are organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism.
• Classification of vitamins: Vitamins are classified into two groups depending upon their solubility in water or fat.

1. Water soluble vitamins i) These vitamins are soluble in water.
   ii) Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and cannot be stored (except vitamin B12) in our body.
   iii) Example: Vitamin C, B group vitamins.
2. Fat soluble vitamins
   i) These vitamins are soluble in fat and oils but insoluble in water.
   ii) They are stored in liver and adipose (fat storing) tissues.
   iii) Example: Vitamin A, D, E and K

Important vitamins, their sources and their deficiency diseases:

Name of vitamins	Sources	Deficiency diseases
Vitamin A	Fish liver oil, carrots, butter and milk	xerophthalmia (hardening of cornea of eye) Night blindness
Vitamin B1 (Thiamine)	Yeast, milk, green vegetables and cereals	Beriberi (loss of appetite, retarded growth)
Vitamin B2 (Riboflavin)	Milk, egg white, liver, kidney	Cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin.
Vitamin B6 (Pyridoxine)	Yeast, milk, egg yolk, cereals and grams	Convulsions
Vitamin B12	Meat, fish, egg and curd	Pernicious anaemia (RBC deficient in haemoglobin)
Vitamin C (Ascorbic acid)	Citrus fruits, amla and green leafy vegetables	Scurvy (bleeding gums)
Vitamin D	Exposure to sunlight, fish and egg yolk	Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults)
Vitamin E	Vegetable oils like wheat germ oil, sunflower oil, etc.	Increased fragility of RBCs and muscular weakness
Vitamin K	Green leafy vegetables	Increased blood clotting time

Class 12 Chemistry Revision Notes Chapter 13 Amines

• Amines: Amines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
• Classification of amines:

• Preparation of amines:

(i) By reduction of nitro compounds: Nitro compounds can be catalytically reduced by passing hydrogen gas in presence of Raney Ni, finely divided Pt or Pd as catalyst at room temperature.

a) 

b) 

Nitro compounds can also be reduced with active metals such as Fe, Sn, Zn etc. with conc. HCl.

a) 

b) 

(ii) By Hoffmann’s method (Ammonolysis of alkyl halides): Reaction of alkyl halides with an ethanolic solution of ammonia in a sealed tube at 373 K forms a mixture of primary, secondary and tertiary amine and finally quarternary ammonium salt. Process of cleavage of C-X bond by ammonia is called ammonolysis.

• The free amine can be obtained from the ammonium salt by treatment with a strong base:
  a) 
  b) 
  c) 
• Order of reactivity of halides is: RI>RBr>RCl
• Larger the size of halogen atom easier is the cleavage of R-X bond
• Limitations of Hoffmann’s method: Method gives mixture of amines which are difficult to separate in a laboratory.
• Methods to get only one product by Hoffmann’s method:

(i) When ammonia is taken in excess primary amine is formed as main product

(ii) When alkyl halide is used in excess quarternary ammonium salt is formed as main product.
Method is not suitable for preparation of aryl amines because aryl amines are relatively less reactive than alkyl halides towards nucleophilic substitution reactions.

(iii) By reduction of nitriles: Nitriles can be reduced to amines using H₂ / Ni , LiAlH₄ or Na(Hg) / C₂H₅ OH

(iv) By reduction of amides: Amides are reduced to corresponding amines by LiAlH4

(v) By Gabriel phthalimide synthesis: Gabriel synthesis is used for the preparation of primary amines. When phthalimide is treated with ethanolic potassium hydroxide, it forms potassium salt of phthalimide which on heating further with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine.

Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with potassium phthalimide.

(vi) By Hoffmann bromamide degradation reaction: Primary amines can be prepared from amides by treatment with Br₂ and KOH. Amine contains one carbon atom less than the parent amide.

• Physical properties of amines:

(i) Solubility: Lower aliphatic amine is soluble in water because they can form hydrogen bonding with water. Solubility decreases with increases in molar mass of amines due to increase in size of hydrophobic group

(ii) Boiling points: Among the isomeric amines primary and secondary amines have high boiling point because they can form hydrogen bonding. Tertiary amine cannot form hydrogen bonding due to the absence of hydrogen atom available for hydrogen bond formation. Hence order of boiling of isomeric amines is Primary>Secondary> Tertiary

• Chemical properties of amines:

(a) Basic character of amines: Amines have an unshared pair of electrons on nitrogen atom due to which they behave as Lewis base. Basic character of amines can be better understood in terms of their K_b and pK_b values

Or 

Greater K_b value or smaller pK_b indicates base is strong.

(b) Comparison of basic strength of aliphatic amines and ammonia: Aliphatic amines are stronger bases than ammonia due to +I effect of alkyl groups leading to high electron density on the nitrogen atom.

(c) Comparison of basic strength of primary, secondary and tertiary amines

(i) The order of basicity of amines in the gaseous phase follows the expected order on the basis of +I effect: tertiary amine > secondary amine > primary amine > NH₃

(ii) In aqueous solution it is observed that tertiary amines are less basic than either primary or secondary amines. This can be explained on basis of following factors:

a) Solvation effect: Greater is the stability of the substituted ammonium cation formed, stronger is the corresponding amine as a base. Tertiary ammonium ion is less hydrated than secondary ammonium ion which is less hydrated than primary amine. Thus tertiary amines have fewer tendencies to form ammonium ion and consequently are least basic.
On the basis of solvation effect order of basicity of aliphatic amines should be primary amine>secondary amine>tertiary amine.

b) Steric factor: As the crowding of alkyl group increases from primary to tertiary amine hinderance to hydrogen bonding increases which eventually decreases the basic strength. Thus there is a subtle interplay of the inductive effect, solvation effect and steric hinderance of the alkyl group which decides the basic strength of alkyl amines in the aqueous state.
When the alkyl group is small like CH₃ there is no steric hindrance to hydrogen bonding. In this case order of basicity in aqueous medium is

When alkyl group is ethyl group order of basicity in aqueous medium is

c) Comparison of basic strength of aryl amines and alkylamines: Generally aryl amines are considerably less basic than alkyl amines .Taking an example of aniline and ethylamine it is observed that ethyl amine is more basic than aniline. In aniline –NH2 group is directly attached to benzene ring. Hence unshared pair of electron on nitrogen is less available for protonation because of resonance. Below mentioned are resonating structures of aniline.

In the above resonating structures there is a positive charge on nitrogen atom making the lone pair less available for protonation. Hence aniline is less basic than ethyl amine which has no resonating structures. Less basicity of aniline can also be explained by comparing the relative stability of aniline and anilinium ion obtained by accepting a proton. Greater the number of resonating structures, greater is the stability of that species.
Aniline is resonance hybrid of five resonating structures whereas anilinium ion has only two resonating structures.

Thus aniline has less tendency to accept a proton to form anilinium ion.

d) Effect of substituent on basic character of amines: Electron donating or electron releasing group/groups (EDG) increases basic strength while electron withdrawing (EWG) decreases basic strength.

• Reactions of amines:

a) Acylation Reaction: Aliphatic and aromatic primary and secondary amines (which contain replaceable hydrogen atoms) react with acid chlorides, anhydrides and esters to form substituted amide. Process of introducing an acyl group (R-CO-) into the molecule is called acylation. The reaction is carried out in the presence of a stronger base than the amine, like pyridine, which removes HCl formed and shifts the equilibrium to the product side.

Since tertiary amine do not contain replaceable hydrogen atom they do not undergo acylation reaction.

b) Carbylamine reaction: Only aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines.

Secondary and tertiary amines do not give the above test.

c) Reaction of primary amine with nitrous acid:
(i) Primary aliphatic amine on reaction with nitrous acid (HNO₂) forms aliphatic diazoniumsalt which decomposes to form alcohol and evolve nitrogen.

(ii) Primary aromatic amines react with nitrous acid (HNO2) in cold (273-278 K) to form diazonium salt.

d) Reaction with benzene sulphonyl chloride: Hinsberg’s reagent-Benzenesulphonyl chloride (C6H5SO2Cl) reacts with primary and secondary amines to form sulphonamides.

The hydrogen attached to nitrogen in sulphonamide formed by primary amine is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.

Since sulphonamide formed by secondary amine does not contain any hydrogen atom attached to nitrogen atom, so it is not acidic. Hence it is insoluble in alkali.

• Ring substitution in aromatic amine: Aniline is more reactive than benzeneand undergoes electrophilic substitution reaction preferably at ortho and para position.

(i) Bromination: Aniline reacts with bromine water at room temperature to give a white precipitate of 2, 4, 6-tribromoaniline

In order to stop reaction at monosubstitution activating effect of –NH2 group is reduced by acetylation. This prevents di and tri substituted products. Acetyl group is removed by hydrolysis.

(ii) Nitration:
(a) Under strongly acidic medium aniline gets protonated to form anilinium ion, which is deactivating group and is meta directing. Hence minitroaniline is also formed in 47% along with ortho and para products.

Aromatic amines cannot be nitrated directly because HNO3 being a strong oxidising agent oxidises it forming black mass.

(b) Nitration by protecting the –NH₂ group by acetylation reaction with acetic anhydride:

iii) Sulphonation: Aniline reacts with conc. H₂SO₄ to form aniliniumhydrogensulphate which on heating with sulphuric acid at 453-473K produces p-aminobenzenesulphonic acid, commonly known as sulphanilic acid, as the major product.

• Reactions of benzene diazonium chloride:
  a) Reactions involving displacement of nitrogen:
  
  b) Reactions involving retention of diazo group, coupling reactions: Diazonium ion acts as an electrophile because there is a positive charge on terminal nitrogen. Therefore benzene diazonium chloride couples with electron rich compounds like phenol and aniline to give azo compounds. Azo compounds contain –N=N- bond and reaction is coupling reaction.
  

Class 12 Chemistry Revision Notes Chapter 12 Aldehydes, Ketones and Carboxylic acid

Aldehydes: Aldehydes are the organic compounds in which carbonyl group is attached to one hydrogen atom and one alkyl or aryl group.

Where R can be an alkyl or aryl group

Preparation of aldehydes:

a) By oxidation of alcohols: Oxidation of primary alcohols in presence of oxidizing agent like K2Cr2O7/H2SO4, KMnO4,CrO3 gives aldehydes.

b) By dehydrogenation of alcohols: When the vapours of primary alcohol passed through heated copper at 573 K, it forms aldehyde.

c) By hydration of alkynes: Ethyne on hydration with  at 333 K forms acetaldehyde.

d) By Rosenmund reduction: Hydrogenation of acyl chloride over palladium on barium sulphate gives aldehyde.

e) By reduction of nitriles:
i) Stephen Reaction: Reduction of nitriles in presence of stannous chloride in presence of HCl gives imine which on hydrolysis gives corresponding aldehyde.

ii) Nitriles are selectively reduced by DIBAL-H (Diisobutylaluminium hydride) to aldehydes.

f) By reduction of ester: Esters are reduced to aldehydes in presence of DIBAL-H (Diisobutylaluminium hydride)

g) From Hydrocarbons:

(i) By oxidation of methyl benzene: Etard Reaction: Chromyl chloride oxidizes methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.

Using chromium oxide: Toluene or substituted toluene is converted to benzaldehyde in presence of chromic oxide in acetic anhydride.

(ii) By side chain chlorination followed by hydrolysis:Halogenation of toluene: Side chain halogenation of toluene gives benzal chloride which on hydrolysis gives Benzaldehyde.

(iii) Gatterman –Koch reaction: Benzene or its derivatives on treatment with carbon monoxide and HCl in presence of anhydrous aluminium chloride or cuprous chloride (CuCl) gives benzaldehyde or substituted benzaldehydes.

• Ketones: Ketones are the organic compounds in which carbonyl group is attached to two alkyl group or aryl group or both alkyl and aryl group.
  
  Where R, R’ may be alkyl or aryl.
• Preparation of ketones:
  a) By oxidation of alcohols: Oxidation of secondary alcohols in presence of oxidizing agent like ,  gives ketones.
  
  b) By dehydrogenation of alcohols: When the vapours of a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and a ketone is formed.
  
  c) By hydration of alkynes: Alkynes on hydration with  at 333 K form ketones.
  
  d) From acyl chloride: Acyl chloride on treatment with dialkyl cadmium (prepared by reaction of cadmium chloride with Grignard reagent) gives ketone.

e) From nitriles: Nitriles on treatment with Grignard reagent followed by hydrolysis give ketones.

f) By Friedel Crafts acylation reaction: Benzene or substituted benzene on treatment with acid chloride in presence of anhydrous aluminium chloride forms ketone.

g) Preparation of aldehydes and ketones by ozonolysis of alkenes:

• Reactions of aldehydes and ketones:

1. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons (or inductive effect).
2. Electronic Effect: Relative reactivities of aldehydes and ketones in nucleophilic addition reactions is due the positive charge on carbonyl carbon. Greater positive charge means greater reactivity. Electron releasing power of two alkyl groups in ketones is more than one in aldehyde. Therefore positive charge is reduced in ketones as compared to aldehydes. Thus ketones are less reactive than aldehydes.
3. Stearic Effect: As the number and size of alkyl group increase, the hindrance to the attack of nucleophile also increases and reactivity decreases. In aldehydes there is one alkyl group and one hydrogen atom, whereas in ketones there are two alkyl groups (same or different).

• Nucleophilic addition reactions of aldehydes and ketones:

(a) Addition of hydrogen cyanide (HCN) to form cyanohydrins

(b) Addition of sodium hydrogensulphiteto form bisulphate addition compound

(c) Addition of Grignard reagent (RMgX) to form alcohol

(d) Addition of alcohol:

(i) Aldehydes on addition of monohydric alcohol in presence of dry HCl forms hemiacetal and acetal.

(ii) Ketones do not react with monohydric alcohols. Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals.

(e) Addition of ammonia and its derivatives:

• Reduction of aldehydes and ketones:

(a) Reduction to alcohols:

Aldehydes and ketones on catalytic hydrogenation in presence of Ni, Pt or Pd by using lithium aluminium hydride  or sodium borohydride  forms primary and secondary alcohols respectively.

(b) Reduction to hydrocarbons:

(i) Clemmensen reduction: Carbonyl group of aldehydes and ketones is reduced to  group on treatment with zinc amalgam and concentrated hydrochloric acid.

(ii) Wolff-Kishner reduction: Carbonyl group of aldehydes and ketones is reduced to  group on treatment with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol.

(iii)

• Oxidation of aldehydes and ketones:

(i) Aldehydes are oxidized to acids in presence of mild oxidising agents HNO3, K2Cr2O7, KMnO4.

(ii) Ketones are oxidized under drastic conditions i.e. with powerful oxidising agents like  at higher temperature.

In case of unsymmetrical ketones cleavage occurs in such a way that keto group stays with smaller alkyl group. This is known as Popoff’s rule.

(iii)Haloform reaction: Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom i.e. methyl ketones are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform.

• Reactions of aldehydes and ketones due to  -hydrogen:

(i) Aldol condensation: Aldehydes and ketones having at least one  -hydrogen undergo a self condensation in the presence of dilute alkali as catalyst to form  -hydroxy aldehydes (aldol) or  -hydroxy ketones (ketol), respectively.

(ii) Cross aldol condensation: Aldol condensation between two different aldehydes and ketones is called aldol condensation. If both of them contain  -hydrogen atoms, it gives a mixture of four products.

• Canizzaro reaction: Aldehydes which do not have an  -hydrogen atom undergo self-oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali to form alcohol and salt of acid.

• Test to distinguish aldehydes and ketones:

1. Tollen’s test: When an aldehyde is heated with Tollen’s reagent it forms silver mirror. Tollen’s reagent is ammoniacal solution of  
   Ketones do not form silver mirror and hence do not give this test.
2. Fehling’s test: When an aldehyde is heated with Fehling’s reagent it formsreddish brown precipitates of cuprous oxide.Fehling’s reagent: Fehling solution A (aqueous solution of ) + Fehling solution B (alkaline solution of sodium potassium tartarate)
   
   Ketones do not give this test.

• Carboxylic Acids:Carboxylic acids are the compounds containing the carboxylfunctional group (-COOH).

• Preparation of carboxylic acid:

(i) From alcohols: Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate  in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7) and chromium trioxide  in acidic media.

a) 

b) 

(ii) From aldehydes: Oxidation of aldehydes in presence of mild oxidizing agents like Tollen’s reagent (ammoniacal solution of ) or Fehling reagent (Fehling solution A (aqueous solution of ) + Fehling solution B (aqueous solution of sodium potassium tartarate)) forms carboxylic acids.

1. 
2. 

(iii) From alkylbenzenes: Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate.

(iv) From alkenes: Suitably substituted alkenes are oxidised to carboxylic acids on oxidation with acidic potassium permanganate or acidic potassium dichromate.

1. 
2. 

(v) From Nitriles: Nitriles on hydrolysis in presence of dilute acids or bases forms amide which on further hydrolysis gives carboxylic acid.

(vi) From Grignard reagent: Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which on hydrolysis forms carboxylic acids.

(vii) From acyl halides and anhydrides: Acid chlorides when hydrolysed with water give carboxylic acids .On basic hydrolysis carboxylate ions are formed which on further acidification forms corresponding carboxylic acids. Anhydrides on hydrolysis forms corresponding acid(s)

(viii) From esters: Acidic hydrolysis of esters gives directly carboxylic acids while basic hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids.

• Physical properties of carboxylic acids:

(i) Solubility: As the size of alky group increases solubility of carboxylic acid decreases because non-polar part of the acid increases

(ii) Boiling points: Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to extensive association of carboxylic acid molecules through intermolecular hydrogen bonding.

• Acidity of carboxylic acids:

Carboxylic acids are more acidic than phenols. The strength of acid depends on extent of ionization which in turn depends on stability of anion formed.

(i) Effect of electron donating substituents on the acidity of carboxylic acids: Electron donating substituent decreases stability of carboxylate ion by intensifying the negative charge and hence decreases acidity of carboxylic acids.

(ii) Effect of electron withdrawing substituent on the acidity of carboxylic acids: Electron withdrawing group increases the stability of carboxylate ion by delocalizing negative charge and hence, increases acidity of carboxylic acid. The effect of the following groups in increasing acidity order is Ph< I < Br <cl< f=””>2 < CF₃</cl<>

(a) Effect of number of electron withdrawing groups: As the number of electron withdrawing groups increases –I effect increases, increasing the acid strength

(b) Effect of position of electron withdrawing group: As the distance between electron withdrawing group and carboxylic group increases, electron withdrawing influence decreases.

• Reaction of carboxylic acids:

Reactions involving cleavage of C-OH bond:

Carboxylic acids on heating with mineral acids such as  or with  give corresponding anhydride.

(i) Anhydride formation:

(ii) Esterification: Carboxylic acids are esterified with alcohols in the presence of a mineral acid such as concentrated  or HCl gas as a catalyst.

(iii) Carboxylic acids react with PCl5, PCl3 and SOCl2 to form acyl chlorides.

1. 
2. 
3. 

(iv) Reaction with ammonia (NH3): Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature gives amides.

i)

ii)

Reactions involving COOH group:

(i) Reduction: Carboxylic acids are reduced to alcohols in presence of LiAlH4 or B2H6.

(ii) Decarboxylation : Sodium or potassium salts of carboxylic acids on heating with soda lime (NaOH + CaO in ratio of 3:1) gives hydrocarbons which contain one carbon less than the parent acid.

(c) Reactions involving substitution reaction in hydrocarbon part:

(i) Hell-Volhard-Zelinsky reaction: Carboxylic acids having an -hydrogen are halogenated at the -position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give -halocarboxylic acids)

(ii) Ring substitution in aromatic acids: Aromatic carboxylic acids undergo electrophilic substitution reactions. Carboxyl group in benzoic acid is electron withdrawing group and is meta directing.

i)

ii)

Class 12 Chemistry Revision Notes Chapter 11 Alcohols, Phenols and Ethers 

• Structure of alcohols:
• Preparation of alcohols:
  a) From alkene
  
  b) From esters
  
  c) From aldehydes and ketones
  
  d) From carboxylic acids
  
• Structure of phenols:

• Preparation of phenols:

a) From benzene

b) From chlorobenzene

c) From cumene

d) From aniline

• Physical properties of alcohols and phenols:

a) Boiling points: Boiling points of alcohols and phenols are higher in comparison to other classes of compounds. This is because the –OH group in alcohols and phenols is involved in intermolecular hydrogen bonding.

The boiling points of alcohols and phenols increase with increase in the number of carbon atoms. This is because of increase in van der Waals forces with increase in surface area.
In alcohols, the boiling points decrease with increase of branching in carbon chain. This is because of decrease in van der Waals forces with decrease in surface area.
b) Solubility: Solubility of alcohols and phenols are soluble in water due to their ability to form hydrogen bonds with water molecules. The solubility of alcohols decreases with increase in size of alkyl/aryl (hydrophobic) groups.

• Chemical properties of alcohols:

I. Reactions involving cleavage of O–H bond: Alcohols react as nucleophiles:
a) Reaction with metals

b) Esterification reaction



II. Reactions of alcohols involving cleavage of carbon – oxygen (C–O) bond:
a) Reaction with hydrogen halides

b) Reaction with phosphorus trihalides

c) Dehydration reaction
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d). Oxidation reaction
i)
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• Chemical properties of phenols:

I. Reactions involving cleavage of O–H bond: Alcohols react as nucleophiles:
a) Reaction with metals

b) Esterification reaction



II. Other chemical reactions of phenols:

III. Acidic nature of phenol and alcohol:
a). Phenol > H2O > Primary alcohol > Secondary alcohol > Tertiary alcohol.
The acidic character of alcohols is due to the polar nature of O–H bond. Alkyl group is an electron-releasing group (–CH3, –C2H5) or it has electron releasing inductive effect (+I effect). Due to +I effect of alkyl groups, the electron density on oxygen increases. This decreases the polarity of O-H bond. And hence the acid strength decreases.

b) Phenol is more acidic than alcohol: In phenol, the hydroxyl group is directly attached to the sp2hybridised carbon of benzene ring which acts as an electron withdrawing group whereas in alcohols, the hydroxyl group is attached to the alkyl group which have electron releasing inductive effect. In phenol, the hydroxyl group is directly attached to the sp2hybridised carbon of benzene ring whereas in alcohols, the hydroxyl group is attached to the sp3hybridised carbon of the alkyl group. The sp2hybridised carbon has higher electronegativity than sp3hybridised carbon. Thus, the polarity of O–H bond of phenols is higher than those of alcohols. Hence, the ionisation of phenols is higher than that of alcohols.
The ionisation of an alcohol and a phenol takes place as follows:

In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the charge is delocalised.

The delocalisation of negative charge makes phenoxide ion more stable and favours the ionisation of phenol. Although there is also charge delocalisation in phenol, its resonance structures have charge separation due to which the phenol molecule is less stable than phenoxide ion.

c) In substituted phenols, the presence of electron withdrawing groups such as nitro group enhances the acidic strength of phenol. On the other hand, electron releasing groups, such as alkyl groups, in general, decreases the acid strength. It is because electron withdrawing groups lead to effective delocalisation of negative charge in phenoxide ion.

• Differentiate between organic compounds:

• Structure of ethers:
  
• Preparation of ethers:

a) From alcohols

b) From alkyl halide and sodium alkoxide

Here, the alkyl halide should be primary and alkoxide should be tertiary. In case of aromatic ether, the aromatic part should be with phenoxide ion.

• Physical properties of ethers

a) Miscibility: Miscibility of ethers with water resembles those of alcohols of the same molecular mass. This is due to the fact that just like alcohols, oxygen of ether can also form hydrogen bonds with water molecule.

b) Boiling points:
Ethers have much lower boiling points than alcohols. This is due to the presence of hydrogen bonding in alcohols. Hydrogen bonding is absent in ethers.

• Chemical properties of ethers:

a) Cleavage of C–O bond in ethers:
R-O-R’ + HX → R-X + R’OH
Excess
The order of reactivity of hydrogen halides is as follows: HI >HBr>HCl
Alkyl halide formed is always the lower alkyl group. But if a tertiary alkyl group is present, the alkyl halide is always tertiary. In case of phenolic ethers, the cleavage occurs with the formation of phenol and alkyl halide.
b) Electrophilic substitution reaction in aromatic ethers:

The electrophilic substitution reaction of aromatic ether involves the following reaction:

• Other conversion reactions:

a) Phenol to salicyldehyde

b) Phenol to benzene diazonium chloride

Class 12 Chemistry Revision Notes Chapter 10 Haloalkanes and Haloarenes

• Nature of C-X bond in alkyl halides: X is more electronegative than carbon. So, the C-X bond is polarized with C having a partial positive charge and X having a partial negative charge.
• Preparation of haloalkanes:

a) 

b) 

c) 

d) Halogen Exchange Method:

• Preparation of haloarenes:

a) By elecrophilic substitution reaction:

b) Sandmeyer’s reaction:

c) Gattermann reaction:

d) From Diazonium Chloride:

e). Balz – Schiemann reaction:

• Physical properties of haloalkanes:

a) Solubility

1. Although haloalkanes are polar in nature, yet they are practically very slightly soluble in water.
2. In order for a haloalkane to dissolve in water, energy is required to overcome the attractions between the haloalkane molecules and break the hydrogen bonds between water molecules.
3. However Haloalkanes are not able to form hydrogen bonds with water and therefore, less energy is released when new attractions are set up between the haloalkane and the water molecules because these are not as strong as the original hydrogen bonds in water molecules.
4. As a result, solubility of haloalkanes in water is low.

b) Density

1. Simple fluoro and chloroalkanes are lighter than water while bromides and polychlorodevrivatives are heavier than water.
2. With the increase in number of carbon atoms, the densities go on increasing. With the increase in number of halogen atoms, the densities go on increasing. The densities increase in the order: Fluoride < chloride < bromide < iodide
3. The density also increases with increasing number and atomic mass of the halogen.

c) Boiling Points

1. Molecules of organic halogen compounds are generally polar.
2. Due to the polarity as well as higher molecular mass as compared to the parent hydrocarbon, the intermolecular forces of attraction (dipole – dipole and van der Waals) between the molecules are stronger in halogen derivatives of alkanes.
3. As a result melting and boiling points of chlorides, bromides and iodides are considerably higher than those of the parent hydrocarbon of comparable molecular mass.
4. For the same alkyl group the boiling points of alkyl chlorides, bromides and iodides follow the order RI >RBr>RCl> RF where R is an alkyl group. This is because with the increase in the size of the halogen, the magnitude of van der Waals force increase.
5. In general, the boiling points of chloro, bromo and iodo compounds increase with increase in the number of halogen atoms.
6. For the same halogen atom, the boiling points of haloalkanes increase with increase in the size of alkyl groups.
7. For isomeric alkyl halides, the boiling points decrease with branching. This is because branching of the chain makes the molecule more compact and, therefore, decrease the surface area. Due to decrease in surface area, the magnitude of van der Waals forces of attraction decreases and consequently, the boiling points of the branched chain compound is less than those of the straight chain compounds.

• Physical Properties of Haloarenes:

a. These are generally colourless liquids or crystalline solids.

b. These are heavier than water.

c. Melting and boiling points of haloarenes
i. Melting and boiling points of haloarenes are nearly the same as those of alkyl halides containing the same number of carbon atoms.
ii. The boiling points of monohalogen derivatives of benzene are in the order: iodo>bromo>chloro>fluoro
iii. For the same halogen atom, the melting and boiling points increase as the size of the aryl group increases.
iv. The melting point of para isomer is quite higher than that of ortho or meta isomers. This is due to the fast that is has symmetrical structure and therefore, its molecules can easily pack loosely in the crystal lattice. As a result intermolecular forces of attraction are stronger and therefore, greater energy is required to break its lattice and it melts at higher temperature.

• Chemical properties of haloalkanes:

Nucleophilic substitution reaction:

Mechanism of Nucleophilic Substitution Reaction:

SN1 Mechanism

1. First order reaction.
2. Rate = k [RX] [Nu]
3. Racemic mixture
4. One step reaction
5. Order: CH3X < 10< 20< 30

SN2 Mechanism

1. Second order reaction
2. Rate = k [RX]
3. Inversion of configuration
4. Two step reaction
5. Order: CH3X > 10> 20> 30

• Elimination reaction: Dehydrohalogentaion(– elimination): When a haloalkane with β-hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from β-carbon and a halogen atom from the α-carbon atom. As a result, an alkene is formed as a product. Zaitsev rule (also pronounced as Saytzeff) is followed.It states that “In dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms.”
• Reaction with metals:

a) Reaction with Magnesium

b) Wurtz reaction

• Chemical properties of haloarenes:

a) Dow’s Process

b) With halogens

c) With conc. nitric and sulphuric acid

d) On heating with conc. sulphuric acid

e) With methyl chloride

f) With acetyl chloride

g) Fittig reaction: 

h) Wurtz – fittig reaction: 

i) Other conversions:

Coordination Compounds Class 12 Notes Chemistry Chapter 9

• Co-ordination compounds:

1. A coordination compound contains a central metal atom or ion surrounded by number of oppositely charged ions or neutral molecules. These ions or molecules re bonded to the metal atom or ion by a coordinate bond.
2. Example: 
3. They do not dissociate into simple ions when dissolved in water.

• Double salt

1. When two salts in stoichiometric ratio are crystallised together from their saturated solution they are called double salts
2. Example:  (Mohr’s salt)
3. They dissociate into simple ions when dissolved in water.

• Coordination entity:

1. A coordination entity constitutes a central metal atom or ion bonded to a fixed number of ions or molecules.
2. Example: In – represents coordination entity.

• Central atom or ion:

1. In a coordination entity, the atom/ion to which a fixed number of ions/groups are bound in a definite geometrical arrangement around it, is called the central atom or ion.
2. Example: In ,  is the central metal ion.

• Ligands:

1. A molecule, ion or group that is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is called ligand.
2. It may be neutral, positively or negatively charged.
3. Examples: etc.

• Donor atom:

1. An atom of the ligand attached directly to the metal is called the donor atom.
2. Example: In the complex ,CN is a donor atom.

• Coordination number:

1. The coordination number (CN) of a metal ion in a complex can be defined as the number of ligand donor atoms to which the metal is directly bonded.
2. Example: In the complex , the coordination number of Fe is 6.

• Coordination sphere:

1. The central atom/ion and the ligands attached to it are enclosed in square bracket and are collectively termed as the coordination sphere.
2. Example: In the complex is the coordination sphere.

• Counter ions:

1. The ions present outside the coordination sphere are called counter ions.
2. Example: In the complex , K+ is the counter ion.

• Coordination polyhedron:

1. The spatial arrangement of the ligand atoms which are directly attached to the central atom/ ion defines a coordination polyhedron about the central atom.
2. The most common coordination polyhedra are octahedral, square planar and tetrahedral.
3. Examples: is square planar,  is tetrahedral while [Cu(NH3)6]3+ is octahedral.

• Charge on the complex ion: The charge on the complex ion is equal to the algebraic sum of the charges on all the ligands coordinated to the central metal ion.
• Denticity: The number of ligating (linking) atoms present in ligand is called denticity.
• Unidentate ligands:

1. The ligands whose only one donor atom is bonded to metal atom are called unidentate ligands.
2. Examples: 

• Didentate ligands:

1. The ligands which contain two donor atoms or ions through which they are bonded to the metal ion.
2. Examples: Ethylene diamine () has two nitrogen atoms, oxalate ion  has two oxygen atoms which can bind with the metal atom.

• Polydentate ligand:

1. When several donor atoms are present in a single ligand, the ligand is called polydentate ligand.
2. Examples: In , the ligand is said to be polydentate and Ethylenediaminetetraacetate ion  is an important hexadentate ligand. It can bind through two nitrogen and four oxygen atoms to a central metal ion.

• Chelate:

1. An inorganic metal complex in which there is a close ring of atoms caused by attachment of a ligand to a metal atom at two points.
2. An example is the complex ion formed between ethylene diamine and cupric ion, .

• Ambidentate ligand:

1. Ligands which can ligate (link) through two different atoms present in it are called ambidentate ligand.
2. Example: and . Here, can link through N as well as O while  can link through S as well as N atom.

• Werner’s coordination theory:

1. Werner was able to explain the nature of bonding in complexes.
2. The postulates of Werner’s theory are:

a). Metal shows two different kinds of valencies: primary valence and secondary valence.

b). The ions/ groups bound by secondary linkages to the metal have characteristic spatial arrangements corresponding to different coordination numbers.

c). The most common geometrical shapes in coordination compounds are octahedral, square planar and tetrahedral.

• Primary valence

1. This valence is normally ionisable.
2. It is equal to positive charge on central metal atom.
3. These valencies are satisfied by negatively charged ions.
4. Example: In , the primary valency is three. It is equal to oxidation state of central metal ion.

• Secondary valence

1. This valence is non – ionisable.
2. The secondary valency equals the number of ligand atoms coordinated to the metal. It is also called coordination number of the metal.
3. It is commonly satisfied by neutral and negatively charged, sometimes by positively charged ligands.

• Oxidation number of central atom: The oxidation number of the central atom in a complex is defined as the charge it would carry if all the ligands are removed along with the electron pairs that are shared with the central atom.
• Homoleptic complexes: Those complexes in which metal or ion is coordinate bonded to only one kind of donor atoms. For example: 
• Heteroleptic complexes: Those complexes in which metal or ion is coordinate bonded to more than one kind of donor atoms. For example: 
• Isomers: Two or more compounds which have same chemical formula but different arrangement of atoms are called isomers.
• Types of isomerism:

a). Linkage isomerism

b). Solvate isomerism or hydrate isomerism

c). Ionisation isomerism

d). Coordination isomerism

1. Structural isomerism
2. Stereoisomerism

a). Geometrical isomerism

b). Optical isomerism

• Structural isomerism:

1. It arises due to the difference in structures of coordination compounds.
2. Structural isomerism, or constitutional isomerism, is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders.

• Ionisation isomerism:

1. It arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion.
2. Example: 

• Solvate isomerism:

1. It is isomerism in which solvent is involved as ligand.
2. If solvent is water it is called hydrate isomerism, e.g.,  and .

• Linkage isomerism:

1. It arises in a coordination compound containing ambidentate ligand.
2. In the isomerism, a ligand can form linkage with metal through different atoms.
3. Example:  and .

• Coordination isomerism:

1. This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex.
2. Example:  and .

• Stereoisomerism: This type of isomerism arises because of different spatial arrangement.
• Geometrical isomerism: It arises in heteroleptic complexes due to different possible geometrical arrangements of ligands.
• Optical isomerism: Optical isomers are those isomers which are non-superimposable mirror images.
• Valence bond theory:

1. According to this theory, the metal atom or ion under the influence of ligands can use its (n-1)d, ns, np or ns, np, nd orbitals for hybridisation to yield a set of equivalent orbitals of definite geometry such as octahedral, tetrahedral, and square planar.
2. These hybridised orbitals are allowed to overlap with ligand orbitals that can donate electron pairs for bonding.

Coordination Number	Type of hybridisation	Shape of hybrid
4		Tetrahedral
4		Square planar
5		Trigonalbipyramidal
6	(nd orbitals are involved – outer orbital complex or high spin or spin free complex)	Octahedral
6	d orbitals are involved –inner orbital or low spin or spin paired complex)	Octahedral

• Magnetic properties of coordination compounds:

A coordination compound is paramagnetic in nature if it has unpaired electrons and diamagnetic if all the electrons in the coordination compound are paired.

Magnetic moment  where n is number of unpaired electrons.

• Crystal Field Theory:

1. It assumes the ligands to be point charges and there is electrostatic force of attraction between ligands and metal atom or ion.
2. It is theoretical assumption.

• Crystal field splitting in octahedral coordination complexes:

• Crystal field splitting in tetrahedral coordination complexes:

• For the same metal, the same ligands and metal-ligand distances, the difference in energy between eg and t2g level is 
• Metal carbonyls:

1. Metal carbonyls are homoleptic complexes in which carbon monoxide (CO) acts as the ligand.
2. Example: 
3. The metal-carbon bond in metal carbonyls possess both s and p character.
4. The M–C  bond is formed by the donation of lone pair of electrons from the carbonyl carbon into a vacant orbital of the metal.
5. The M–C bond is formed by the donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding orbital of carbon monoxide.
6. The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and the metal.