Imperial Study

CBSE Class-12 Chemistry
Quick 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 diagnosis, prevention and
  treatment of diseases
• Therapeutic effect: Desirable or beneficial effect of a drug like 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:

1. 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.
2. 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.

1. 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.

Ar I 1 ■ ■ r■ blli> ur| I fl

• 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:

1. 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.
2. 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).
3. 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:

1. Non-narcotic analgesics: They are non-addictive drugs. Examples: Aspirin,
   Ibuprofen, Naproxen, Dichlofenac Sodium.
2. Narcotic analgesics: When administered in medicinal doses, these drugs relieve
   pain and produce sleep. Examples: Morphine and its derivatives
3. 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.
4. Anti-fertility Drugs: Chemical substances used to prevent conception or fertilization
   are called anti-fertility drugs. Examples – Norethindrone, ethynylestradiol (novestrol).

• Types of antimicrobial drugs :

1. 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 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
4. 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.
5. 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.

CH₂^H
!

o

CH₂– O-C-C₁₇H_3s
I O

M

CH – O – C – C₁₇H_js + 3NaOH

I O

J _A [1 * .,

CH₂– O-C-C₁₇H_js

Glyceryl ester Sodium

of stearic acid (Fat) hydroxide

» 3C_iyH_JSCOONa + CH -OH

I

(Soap) CH₁^H

Sodium Gtycerol

stearate

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. Insome 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.

1. Soap granules are dried miniature soap bubbles.
2. Soap powders and scouring soaps contain some soap, a scouring agent (abrasive) such as
   powderedpumice 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 white
  precipitate of calcium and magnesium salts

2C₁₇H_yCOONa-CaCl- ^ % NaCl– Ca

^oap ftGoltfbte Cd L. Lur.

::=:^i:r (ioap)

2C-H_3jCOOXa+MgCl₃ ^2 NaCl-(C-H_3jCOO)₃Mg

iQap ir.E■:■ It’Dh ™ zr.dE i.um

E-[ddfd te (EC-Erp)

These precipitates stick to the fibres 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:

1. 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.

1. Cationic detergents: Cationic detergents are quarternary ammonium salts of a mines 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.
2. 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.

CBSE Class-12 Chemistry
Quick 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
2. Natural polymers: Polymers obtained from nature, mostly plants and animals.
   Examples – Cellulose, starch, etc.
3. Synthetic polymers: Polymers prepared in laboratory. Examples – Teflon, Nylon 6,6 ,
   Synthetic rubber (Buna – S) etc.
4. Semi synthetic polymers: Polymers derived from naturally occurring polymers by
   carrying out chemical modifications. Examples – Rayon (cellulose acetate), cellulose
   nitrate, etc.
5. Based on the structure of polymer, it is classified into
6. Linear polymers: Polymer consists of long and straight chains. Examples – High
   density polythene, polyvinyl chloride, etc.
7. Branched chain polymers: Polymers contains linear chains having some branches.
   Examples – Low density polythene
8. 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.
9. Based on the mode of polymerisation, it is classified into
10. 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.

1. 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

O O O

Ii fus I il . *

<VJ,^KW>C-Crt >2C^>0^-2CA +2C0,

Bcnznyi pmaKk ETwmi redjcaJ

* ■

C*H*+CHj=CKt * CJi,-CJi_:-CH_L

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.

C_iH_i ~ CH₁ – C H₁ – CH₁ = CH₁

4 .

CJi_i – CH₁ – CH₁ – CH₁ – C H₁

4

¥

C_iH_i – CCH₁ – CH^ – CH₁ – C H₁

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:

1. . 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

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

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

1. . Polytetrafluoroethene (is a polymer of Teflon)

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

1. . 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.

KHOOC(CH₂)₄COOH+ }TH₂H(CH_:)^XH₂

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

CupraUcLam

It is used for the manufacture of tyre cords, fabrics and ropes.

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

n HOHt- CH₁OH t n HOOCn0- COOH —*

Efl^DK^ol TerepbLhabc ^rid

|Etha^!.2’dKfl (BmrKie-!.4 – dl

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.

1. 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

1. 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.

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

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)

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

1. 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:

CBSE Class-12 Chemistry
Quick Revision Notes
Chapter 14
Biomolecules

• Carbohydrates: Polyhydroxy aldehydes or polyhydroxyketones or compounds on
  hydrolysis give carbohydrates.
• Classification of carbohydrates:

Monosaccharides

1. Simplest carbohydrates
2. It cannot be hydrolysed into simpler compounds
3. Examples – Glucose, mannose
   Oligosaccharides
4. Carbohydrates which gives 2 to 10 monosaccharide units on hydrolysis
5. Examples – Sucrose, Lactose, Maltose
   Polysaccharides
6. Carbohydrates which on hydrolysis give large number of monosaccharide units.
7. Examples – Cellulose, starch

• Anomers: Pair of optical isomers which differ in configuration only around C1 atom
  are called anomers. Examples – c*-D-glucopyranose and /3-D-glucopyranose.
• Epimers: Pair of optical isomers which differ in configurationaround 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

CHO – (CHQR-)< – CH₂OH

• Structure elucidation of glucose:

1. D – glucose with HI

b) D – glucose with HCN

c) D – glucose with NH2OH

d) D- glucose with Fehling’s reagent

/ 15

e) D – glucose with Tollen’s reagent

f) D – glucose with nitric acid

1. D – glucose with (CH3CO)2O and ZnCl2

/ 15

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 Schiffs 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. ^[1]

1. Sucrose is a non-reducing sugar because the two monosaccharide units are held together
   by a glycosidic linkage between C1 of ct-glucose and C2 of /3- fructose. Since the reducing
   groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non-
   reducing sugar.

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

^^Ci^Hu°i^+C‘^Ru⁰–
D-%izcon D- r>urtare
[*.;.,-+:V^ Iafc_rJH^

• Haworth Projection of Sucrose:

• Haworth projection of maltose:

• Lactose (Milk sugar):It is composed of p-D-galactose and p-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 a-D-(+)- glucose units held by a- 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 /3-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.

R-CH-COOH

L

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

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

• Zwitter ion 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 zwitter ionic form, amino acids show amphoteric behaviour as they react both with
   acids and bases.

O O

R-CH-C-O-H^R- CH-C-O-

jffiR W₁

2 j

■JSi iiii^ ioa^

• 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 a-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:

a- 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.

1. C = O and N – H group of the peptide bonds are trans to each other.
2. Ramchandran angles ($and^) – $angle which C^makes with N – H and Wangle which
   (7_amakes with C = O.

/3- 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- … + NH^)
4. Hydrophobic interactions
5. van der Waals forces

• Two shapes of proteins:

Fibrous proteins

1. When the polypeptide chains run parallel and are held together by hydrogen and
   disulphide bonds, then fibre- like structure is formed.
2. These proteins are generally insoluble in water
3. Examples: keratin (present in hair, wool, silk) and myosin (present in muscles), etc
   Globular proteins
4. This structure results when the chains of polypeptides coil around to give a spherical
   shape.
5. These are usually soluble in water.
6. 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

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 ct-helix structure in which two strands are coiled spirally in
   opposite directions.
2. Sugar present is /3-D-2-deoxyribose
3. Bases:
4. Purine bases: Adenine (A) and Guanine (G)
5. Pyrimidine bases: Thymine (T) and cytosine (C)
6. It occurs mainly in the nucleus of the cell.
7. It is responsible for transmission for heredity character.

RNA

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

1. Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds
   with guanine.
2. Diameter of double helix is 2 nm.
3. Double helix repeats at intervals of 3.4 nm. (One complete turn)
4. 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
2. These vitamins are soluble in water.
3. 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.
4. Example: Vitamin C, B group vitamins.
5. Fat soluble vitamins
6. These vitamins are soluble in fat and oils but insoluble in water.
7. They are stored in liver and adipose (fat storing) tissues.
8. Example: Vitamin A, D, E and K

• Important vitamins, their sources and their deficiency diseases:

• Maltose:

Maltose is composed of two a-D-glucose units in which C1 of one glucose (I) is linked to C4
of another glucose unit (II).

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.

1. Sucrose (invert sugar): ↑

CBSE Class-12 Chemistry
Quick 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.

Ni,Pt or pd

a)

Ni, Pt or pd

b)

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

Sn/HCl or Fe/HCl

a)

Sn/HCl or Fe/HCl

1. Ar — NO2 + 3.¾ >■ Ar — iVfl2 + 2.¾ 0

(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.

+■ —

RNH₂ — > R₂NH ^f–^l: > R₃N ^K>: > S₄ A⁷ X

(£) (2^e) (j^e) Q*at9T#nrj/.

3Tjy.PT.LUTL E-L |[ I

• The free amine can be obtained from the ammonium salt by treatment with a strong
  base:

NaOH

a)

(l°a min e)

NaOH

b)

(2°amine)

NaOH

c)

(3° a min e)

• 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:

1. When ammonia is taken in excess primary amine is formed as main product
2. 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.

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

H₂/Ni

Or

Na(Hg)/C₂H₅OH

Or

LiAlHt

R-C = N >R-CH₂ -NH₂

1. By reduction of amides: Amides are reduced to corresponding amines by LiAlH4

1. 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.

1. 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.

0

Il

R – C- NH₂ + Br₂ + ANaOH

i

R – NH₂ + Na₂ CO₂ + 2 NaBr + 2 H₂O

Physical properties of amines:

1. 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
2. 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:

1. 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 Kb and pKb values

R – NH₂ + H₂O <* R – NH₃ + OH

[.R-NH_z][OH]
[R-NH₂][H₂0\

[R-NHs][OH]

Or K[H₂0] =

[R-NH₂]

_ [R-NH₃][OH]
^b [R-NH₂]

pKb = -Iogif₆

Greater Kb value or smaller pKb indicates base is strong.

1. 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.
2. 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:

1. 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.

1. 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

(CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃

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

(C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃

1. 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.

1. 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.

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.

Base

R – NH₂ + RCOCl > RNHCOR + HCl

Add chloride Substituted amide

R ‘NHCOR+ RCOOH

^Li bzmwed em^

R₂ NH + RCOCl — ——* HCl

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.

R – NH₀ + CHCl + 3 KOH

2. .-

|

1 F

R – NC + 3KCl + ^H₂O

Secondary and tertiary amines do not give the above test.

1. 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.

1. 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.

NO_j

(51¾) (47%) (2%)

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 ofbenzene diazonium chloride:

a) Reactions involving displacement of nitrogen:

Material Downloaded From SUPERCOP

/ 11

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.

CSBE 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:

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

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

1. By hydration of alkynes: Ethyne on hydration withat 333 K forms

acetaldehyde.

1. By reduction of nitriles:

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

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

^T/

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

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

1. From Hydrocarbons:
2. By oxidation of methyl benzene: Etard Reaction: Chromyl chloride {CrO2Cl2) oxidizes
   methyl group to a chromium complex, which on hydrolysis gives corresponding
   benzaldehyde.

Using chromium oxide(Cr03): Toluene or substituted toluene is converted to benzaldehyde
in presence of chromic oxide in acetic anhydride.

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

1. 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.

1. From acyl chloride: Acyl chloride on treatment with dialkyl cadmium (prepared by
   reaction of cadmium chloride with Grignard reagent) gives ketone.

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

1. By Friedel Crafts acylation reaction: Benzene or substituted benzene on treatment with
   acid chloride in presence of anhydrous aluminium chloride forms ketone.
2. Preparation of aldehydes and ketones by ozonolysis of alkenes:

^^tK

l I

C=C —
Propene

+ O₁– ^ —C C —

E 1

O — O

o*oni<3c

| Zn + I ^O

i I

— C = O + O = C —

Ald&bydes orKetones

• 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 hydrogensulphite(^a#,L>O3)to form bisulphate addition compound

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

(d) Addition of alcohol:

1. Aldehydes on addition of monohydric alcohol in presence of dry HCl forms hemiacetal
   and acetal.

1. 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 {LiAlH4) or sodium borohydride (NaBH4) forms primary
and secondary alcohols respectively.

(b) Reduction to hydrocarbons:

1. Clemmensen reduction: Carbonyl group of aldehydes and ketones is reduced to CH^
   group on treatment with zinc amalgam and concentrated hydrochloric acid.

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

(iii)

R-COOHH- J? -CH_zCOOH

(By dfav^e OiC_t-C^wif)

+

R-CH_zCOOH +R -COOH

(j5T ■: lMV15* of Cj – Cjiw*J)

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

1. 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 a -hydrogen:

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

1. Cross aldol condensation: Aldol condensation between two different aldehydes and
   ketones is called aldol condensation. If both of them contain a -hydrogen atoms, it gives a
   mixture of four products. ^[1]

• 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 AgNO3

Mi&+%j£m₃)/+3ar ^Rcvai-24g+2H,o+4XH,

Ketones do not form silver mirror and hence do not give this test.

1. 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
   CuSO4) + Fehling solution B (alkaline solution of sodium potassium tartarate)
   R-CH0+2Cu¹⁺+50H~^RC00-+ Cu₂O +3 H₂O

Kfc^-&n*n ppl

Ketones do not give this test.

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

0

I!

R OH
CarboxyUc auid

• Preparation of carboxylic acid:

(i) From alcohols: Primary alcohols are readily oxidised to carboxylic acids with common
oxidising agents such as potassium permanganate {KMnO4) in neutral, acidic or alkaline
media or by potassium dichromate (K2Cr2O7) and chromium trioxide (CrO3) in acidic

media.

1. From aldehydes: Oxidation of aldehydes in presence of mild oxidizing agents like Tollen’s
   reagent (ammoniacal solution of AgNOs) or Fehling reagent (Fehling solution A (aqueous
   solution of CuSO4) + Fehling solution B (aqueous solution of sodium potassium tartarate))
   forms carboxylic acids.

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

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

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

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

1. 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)

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

1. Solubility: As the size of alky group increases solubility of carboxylic acid decreases
   because non-polar part of the acid increases
2. 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.

1. 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.
2. 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 2 < CF3
3. Effect of number of electron withdrawing groups: As the number of electron withdrawing
   groups increases -I effect increases, increasing the acid strength
4. 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 H2SO4 or with P2O5 give
corresponding anhydride.

(i) Anhydride formation:

(ii) Esterification: Carboxylic acids are esterified with alcohols in the presence of a mineral
acid such as concentrated H2SO4 or HCl gas as a catalyst.

Auirnoniuin benzoatc Lfcnutmidc

Reactions involving COOH group:

1. Reduction: Carboxylic acids are reduced to alcohols in presence of LiAlH4 or B2H6.

1. 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.

1. Reactions involving substitution reaction in hydrocarbon part:

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

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