Chemistry Part II

Class 12 Chemistry Chapter 6 covers Haloalkanes and Haloarenes — organic compounds formed by replacing hydrogen atoms in hydrocarbons with halogen atoms — explaining their classification, nomenclature, preparation methods, physical properties, and key reactions including nucleophilic substitution (SN1 and SN2), elimination, and reactions with metals.

• 1Haloalkanes have halogen bonded to sp3-hybridised carbon; haloarenes have halogen bonded to sp2-hybridised carbon of an aromatic ring.
• 2Alkyl halides are best prepared from alcohols using thionyl chloride (preferred, gives pure product), phosphorus halides or halogen acids; aryl halides are made by electrophilic substitution or Sandmeyer's reaction.
• 3The C–X bond length and bond enthalpy trend follows C–F > C–Cl > C–Br > C–I in bond strength, while boiling points follow RI > RBr > RCl > RF due to increasing van der Waals forces.
• 4SN2 reactions proceed with inversion of configuration and favour primary halides; SN1 reactions proceed via a planar carbocation intermediate leading to racemisation and favour tertiary halides.
• 5Haloarenes are far less reactive than haloalkanes towards nucleophilic substitution due to resonance (partial C–Cl double-bond character), shorter C–X bond length (169 pm vs 177 pm), and instability of the phenyl cation.

Class 12 Chemistry Chapter 7 covers alcohols, phenols and ethers — their classification, IUPAC nomenclature, preparation methods, physical properties, and chemical reactions including acidity, esterification, dehydration, oxidation, and electrophilic aromatic substitution.

• 1Alcohols are classified as primary, secondary or tertiary based on the carbon bearing the –OH group, and as monohydric, dihydric or trihydric based on the number of –OH groups.
• 2Phenols are stronger acids than alcohols (phenol pKa ≈ 10.0; ethanol pKa ≈ 15.9) because the phenoxide ion is stabilised by delocalisation of the negative charge into the aromatic ring.
• 3Alcohols are prepared by acid-catalysed hydration of alkenes (Markovnikov addition), hydroboration-oxidation (anti-Markovnikov), reduction of aldehydes/ketones/carboxylic acids, and reaction of Grignard reagents with carbonyl compounds.
• 4Phenols are prepared industrially from cumene (cumene hydroperoxide route), and in the laboratory from haloarenes (fusion with NaOH), benzenesulphonic acid, or diazonium salts.
• 5Ethers are synthesised by dehydration of primary alcohols at 413 K or by Williamson synthesis (SN2 reaction of sodium alkoxide with a primary alkyl halide); Williamson synthesis also works for unsymmetrical ethers.

NCERT Class 12 Chemistry Chapter 8 covers aldehydes, ketones, and carboxylic acids — polar carbonyl-group compounds central to organic synthesis, biochemistry, and industrial applications such as solvents, perfumes, plastics, and food preservatives.

• 1Aldehydes are more reactive than ketones in nucleophilic addition reactions due to both steric (one vs. two bulky substituents) and electronic (greater electrophilicity of carbonyl carbon) factors.
• 2Aldehydes are distinguished from ketones using mild oxidising agents: Tollens' reagent gives a silver mirror with aldehydes; Fehling's reagent gives a reddish-brown precipitate (aromatic aldehydes do not respond to Fehling's test).
• 3Aldehydes and ketones with at least one α-hydrogen undergo aldol condensation in dilute alkali to give β-hydroxy aldehydes or ketones; aldehydes without α-hydrogen undergo Cannizzaro reaction (disproportionation) with concentrated alkali.
• 4Carboxylic acids are significantly more acidic than alcohols and phenols; electron-withdrawing substituents increase acidity by stabilising the carboxylate anion, while electron-donating groups decrease it.
• 5Carboxylic acids are prepared by oxidation of primary alcohols and aldehydes, hydrolysis of nitriles and esters, treatment of Grignard reagents with CO2, and side-chain oxidation of alkylbenzenes.

Chapter 9 of Class 12 Chemistry Part II covers amines — organic compounds derived from ammonia by replacing one, two, or all three hydrogen atoms with alkyl or aryl groups — and diazonium salts, key intermediates in synthesising aromatic compounds including azo dyes.

• 1Amines are classified as primary, secondary, or tertiary based on how many hydrogen atoms of ammonia are replaced by alkyl/aryl groups; nitrogen is sp3 hybridised with a pyramidal shape.
• 2Aliphatic amines are stronger bases than ammonia (pKb 3–4.22) due to the electron-releasing +I effect of alkyl groups; aromatic amines are weaker bases (aniline pKb 9.38) because the lone pair conjugates with the benzene ring.
• 3Six major preparation methods include reduction of nitro compounds, ammonolysis of alkyl halides, reduction of nitriles and amides, Gabriel phthalimide synthesis (primary amines only), and Hofmann bromamide degradation (amine has one fewer carbon than the amide).
• 4The carbylamine reaction (foul-smelling isocyanide formation with CHCl3/KOH) is a distinguishing test exclusive to primary amines; Hinsberg's reagent (benzenesulphonyl chloride) differentiates all three classes.
• 5Diazonium salts (ArN2+X–) are formed by diazotisation of primary aromatic amines with NaNO2/HCl at 273–278 K; they undergo Sandmeyer, Gattermann, and coupling reactions to introduce a wide range of substituents.

Biomolecules are complex organic molecules — including carbohydrates, proteins, nucleic acids, lipids, vitamins, and hormones — that form the structural and functional basis of all living systems.

• 1Carbohydrates are polyhydroxy aldehydes or ketones classified as monosaccharides, disaccharides, or polysaccharides based on hydrolysis behaviour; sucrose on hydrolysis yields glucose and fructose
• 2Glucose (C6H12O6) is an aldohexose that exists in open-chain and cyclic (pyranose) forms; the two cyclic anomers are called alpha- and beta-glucose
• 3Proteins are polymers of about 20 alpha-amino acids joined by peptide bonds; essential amino acids (10 in number) cannot be synthesised by the body and must come from diet
• 4DNA contains deoxyribose sugar and the base thymine, whereas RNA contains ribose sugar and uracil; adenine pairs with thymine and cytosine pairs with guanine in DNA's double helix
• 5Vitamins A, D, E, and K are fat-soluble (stored in liver and adipose tissue); B-group vitamins and vitamin C are water-soluble and must be regularly supplied in diet