Organic Chemistry covers the synthesis, reactions, and analysis of carbon compounds — from alkanes through functional group interconversions to spectroscopic identification — the largest topic area in IAL Chemistry.
Alkanes: free radical substitution (UV + Cl₂). Initiation → propagation → termination. Alkenes: electrophilic addition (HBr, H₂O/H⁺, Br₂, H₂/Ni). Markovnikov\'s rule for unsymmetrical alkenes. Test: decolourises bromine water. Halogenoalkanes: nucleophilic substitution — SN1 (tertiary, carbocation intermediate) or SN2 (primary, one-step). Nucleophiles: OH⁻ (→ alcohol), CN⁻ (→ nitrile, extends chain), NH₃ (→ amine). Elimination with hot ethanolic NaOH (→ alkene). Alcohols: oxidation with acidified dichromate. Primary → aldehyde (distil) → carboxylic acid (reflux). Secondary → ketone. Tertiary → no reaction. Dehydration (conc H₂SO₄ or Al₂O₃ catalyst) → alkene. Esterification: alcohol + carboxylic acid (H⁺ catalyst, reflux) → ester + H₂O.
Carbonyls: aldehydes and ketones. Test with 2,4-DNPH (orange precipitate). Tollen\'s reagent (silver mirror = aldehyde). Reduction with NaBH₄ → alcohol. Nucleophilic addition with HCN (→ hydroxynitrile). Carboxylic acids: weak acids. React with bases, carbonates, reactive metals. Esters: fruity smells, used as solvents. Hydrolysis: acid or base. Amines: bases (lone pair on N). Preparation from halogenoalkane + NH₃. Aromatic amines from nitrobenzene (Sn/HCl). Amino acids: zwitterions, optical isomerism (except glycine). Condensation polymers: polyesters, polyamides (nylon). Isomerism: structural, E/Z (geometric), optical (chiral carbon). Spectroscopy: mass spec (molecular ion M⁺, fragmentation). IR: broad O-H (alcohol 3200-3550, acid 2500-3300), C=O (1680-1750). ¹H NMR: chemical shift (δ), integration (ratio of H atoms), splitting (n+1 rule). ¹³C NMR: number of carbon environments.
SN2 (bimolecular nucleophilic substitution): one step — the nucleophile attacks the carbon at the same time as the leaving group departs. Rate = k[halogenoalkane][nucleophile]. Favoured by primary halogenoalkanes (less steric hindrance). Produces inversion of configuration at the chiral centre. SN1 (unimolecular): two steps — (1) the leaving group departs to form a carbocation intermediate (rate-determining), then (2) the nucleophile attacks. Rate = k[halogenoalkane] (first order). Favoured by tertiary halogenoalkanes (stable carbocation due to inductive effect of three alkyl groups). Produces a racemic mixture (50:50 enantiomers) because the nucleophile can attack either side of the planar carbocation. Secondary halogenoalkanes can go by either mechanism. Solvent also matters: polar protic solvents favour SN1; polar aprotic favour SN2.
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