Organic Chemistry at A Level covers homologous series, functional group chemistry, and detailed reaction mechanisms — the language of how and why organic reactions happen.
Homologous series: same functional group, same general formula. Nomenclature: IUPAC naming (root = longest chain, prefix/suffix for functional groups). Isomerism: structural (chain, position, functional group) and stereoisomerism (E/Z geometric, optical). Functional groups: C=C (alkene), -OH (alcohol), -X (halogenoalkane), C=O (carbonyl), -COOH (carboxylic acid), -NH₂ (amine), -COOR (ester), -CONH- (amide).
Free radical substitution: alkanes + halogens (UV light). Initiation → propagation → termination. Electrophilic addition: alkenes + HBr, Br₂, H₂O (acid catalyst). Markownikoff\'s rule (carbocation stability). Nucleophilic substitution: halogenoalkanes + OH⁻/CN⁻/NH₃. SN1 (tertiary, carbocation intermediate) vs SN2 (primary, one-step, inversion). Elimination: halogenoalkanes + OH⁻ in ethanol → alkene. Electrophilic substitution: benzene + Br₂/FeBr₃, HNO₃/H₂SO₄ (nitration), RCOCl/AlCl₃ (acylation).
Alcohols: oxidation (primary → aldehyde → carboxylic acid, secondary → ketone, tertiary resistant). Reagent: acidified K₂Cr₂O₇. Dehydration → alkene. Ester formation with carboxylic acid. Carbonyls: aldehydes + Tollens → silver mirror, + Fehling → red precipitate. Ketones do not react (distinguishing test). Both react with 2,4-DNPH → orange precipitate. Carboxylic acids: weak acids, react with bases, carbonates, alcohols. Amines: bases, react with acids. Condensation polymers: polyesters (-COOH + -OH), polyamides (-COOH + -NH₂).
SN1 (substitution nucleophilic unimolecular): favoured by tertiary halogenoalkanes (stable 3° carbocation intermediate), polar protic solvents (stabilise carbocation), weak nucleophiles. Two-step mechanism: slow step forms carbocation, fast step nucleophile attacks. Rate = k[halogenoalkane]. SN2 (substitution nucleophilic bimolecular): favoured by primary halogenoalkanes (less steric hindrance), polar aprotic solvents, strong nucleophiles (OH⁻, CN⁻). One-step mechanism: nucleophile attacks from opposite side as leaving group departs. Rate = k[halogenoalkane][nucleophile]. Secondary halogenoalkanes: mixture of both pathways.
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