UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper II

Q6(c)(ii). (S)-3-Phenylbutan-2-one with m-CPBA

10 marks
Topic: Synthetic uses of reagents
Answered

Question

Write the major and minor products in the following reaction. Discuss the stereochemistry along with reaction mechanism for the formation of the major product: (S)-3-phenylbutan-2-one treated with m-CPBA. [structure given in the paper]

Answer in brief

Major: (S)-1-phenylethyl acetate (the secondary benzylic group migrates, with retention of configuration); minor: methyl (S)-2-phenylpropanoate (methyl migrates).

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Topic notes: reagents for oxidation, reduction and hydroboration, with every Civil Services, IFoS and Geo-Scientist PYQ →

Topic notes: stereochemistry and conformational analysis (R/S, E/Z, Fischer and Newman projections, cyclohexane chair), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversBaeyer–Villiger oxidationm-CPBACriegee intermediatemigratory aptituderetention of configuration

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