Q6(a)(ii). Photolysis of 4,5-dimethylheptan-2-one
Giving justification, write the major and minor product(s) of the photolysis (hν) of the given ketone. Comment upon the chirality of recovered reactant (if any). [structure of optically active 4,5-dimethylheptan-2-one given in the paper]
Answer in brief
Major: acetone + 3-methylpent-2-ene (E and Z), via the tertiary γ-H at C-5; minor: 3-methylpent-1-ene and a cyclobutanol (Yang); recovered ketone is epimerised at C-5, C-4 retained.
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CoversNorrish type IIYang cyclisation1,4-biradicalepimerisationphotochemistry of ketones
All parts of Question 6
- 6(a)(i) Photolysis of a mixture of valerophenone and 5,5-dideuteriohexan-2-one5 marks
- 6(a)(ii) Photolysis of 4,5-dimethylheptan-2-one10 marks
- 6(b)(i) Polypropylene by Ziegler–Natta catalysis10 marks
- 6(b)(ii) Perlon (nylon-6) from ε-caprolactam5 marks
- 6(c)(i) OsO₄, then HIO₄, on an alkenyl cyclopropane lactone10 marks
- 6(c)(ii) (S)-3-Phenylbutan-2-one with m-CPBA10 marks