2025 VJC JC2 H2 Organic Revision Lecture (students)

1 VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT JC2 H2 CHEMISTRY ORGANIC CHEMISTRY REVISION LECTURE OUTLINE S/N TOPIC PAGE 1 Reaction Mechanisms 2 – 4 2 Hybridisation 4 – 5 3 Isomerism 5 – 7 4 Acidity and Basicity of Organic Compounds 7 – 10 5 Hydrolysis Reactions (relative rate) 11 6 Environmental Concerns of Organic Compounds 11 – 12 7 Amino Acids 12 – 14 8 Reactions of Organic Compounds by Homologous Series 15 – 21 9 Reactions of Organic Compounds by Reagents and Conditions 22 – 29 10 Structural Elucidation 29 – 31 11 Practice Questions (Assigned on SLS) -

2 1. REACTION MECHANISMS (a) Mechanism: Free radical substitution Stoichiometric equation: CH4 + Cl2 → CH3Cl + HCl Mechanism: Initiation: Generation of free radicals. Cl Cl 2Cluv Propagation: Free radicals generate other free radicals. Termination: Free radicals combine to form molecules. (b) Mechanism: Electrophilic addition Stoichiometric equation: CH3CH=CH2 + Br2 → CH3CHBrCH2Br Mechanism: CH3 C C H H H + Br Br + - CH3 C H C H H Br + Br N.B.: The most stable carbocation intermediate will be formed (Markovnikov’s rule). In the case, Br is attached to C with more hydrogen atoms to form the more stable carbocation. Relative stability of carbocations: tertiary > secondary > primary, because alkyl groups exert electron – donating inductive effect which disperse the positive charge on the carbocation, stabilising the carbocation. CH3 CH CH2 Br+ + Br- CH3 CH CH2 Br Br (c) Mechanism: Electrophilic substitution Stoichiometric equation: + HNO3 → NO2 + H2O Mechanism: Generation of strong electrophile: 2H2SO4 + HNO3 → 2HSO4− + NO2+ + H3O+ nitronium ion + NO2 + H NO2 + H NO2 + + HSO4 - NO2 + H2SO4 Brønsted- Lowry acid catalyst H2SO4 regenerated. For chlorination, bromination and Friedel – Crafts alkylation, Lewis acid catalysts (e.g anhydrous AlCl3 or FeBr3) are used to form strong electrophiles. (d) Mechanism: Nucleophilic addition Stoichiometric equation: H H R–C + HCN → R–C–OH O CN Mechanism: Catalyst CN‒ regenerated. CN‒ slow fast uv Cl HCl Cl Cl Cl CH3Cl Cl Cl Cl Cl CH3Cl

3 (e)(i) Mechanism: Bimolecular nucleophilic substitution, SN2 (for primary RX) Stoichiometric equation: CH3CH2Cl + NaOH(aq) → CH3CH2OH +NaCl Mechanism: Factors favouring the mechanism Low steric hindrance [due to less alkyl groups attached to electron deficient carbon atom] – usually favoure