Q2(a)(ii). Primary and secondary kinetic isotope effects
Identify the above reactions that show primary kinetic isotope effect and secondary kinetic isotope effect. [four reactions (A)–(D) given in the paper: (A) PhCH₂–H* + Br· → PhĊH₂ + H*–Br; (B) addition of HCN; (C) a retro-Diels–Alder reaction; (D) a Hofmann elimination with ⁻OH giving Me₃N + H*–OH]
Answer in brief
Primary: (A) and (D); the C–H* bond breaks in the rate-determining step. Secondary: (B) and (C); the C–H* bond stays intact.
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Coverskinetic isotope effectprimary isotope effectsecondary isotope effectkH/kDzero-point energy
All parts of Question 2
- 2(a)(i) Aromatic, antiaromatic or non-aromatic by the Hückel rule5 marks
- 2(a)(ii) Primary and secondary kinetic isotope effects5 marks
- 2(a)(iii) Enolates of butan-2-one: NaOMe versus LDA5 marks
- 2(b)(i) Hydrolysis of bis(2-chloroethyl) sulfide and of 1,5-dichloropentane5 marks
- 2(b)(ii) Both glycosyl bromides give the β-glycoside5 marks
- 2(b)(iii) Ketene, hν, then cis-but-2-ene10 marks
- 2(c)(i) Acetolysis of 2-(cyclopent-3-enyl)ethyl tosylate10 marks
- 2(c)(ii) Indole: electrophilic substitution at C-3, not C-25 marks