3,4-Dimethylhexane-3,4-diol, CH3CH2-C(OH)(CH3)-C(OH)(CH3)-CH2CH3, is heated with dilute acid. Assuming ethyl migrates in preference to methyl, the main product is

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JEE Main levelSingle correct optionDifficulty 2 of 3ap091

3,4-Dimethylhexane-3,4-diol, $CH X_{3} CH X_{2} - C (OH) (CH X_{3}) - C (OH) (CH X_{3}) - CH X_{2} CH X_{3}$ , is heated with dilute acid. Assuming ethyl migrates in preference to methyl, the main product is

A3,4-dimethylhex-3-ene
B3,4-dimethylhexanal
C3-ethyl-3-methylpentan-2-one
D4,4-dimethylhexan-3-one

Answer: C

The diol is symmetrical, so ionisation of either OH gives the same type of tertiary cation. Of the two groups on the neighbouring carbinol carbon, ethyl and methyl, ethyl migrates better. The cationic carbon becomes

C (CH X_{3}) (Et) X_{2}

and the other carbon becomes

C (= O) CH X_{3}

, giving

CH X_{3} CO - C (CH X_{3}) (CH X_{2} CH X_{3}) X_{2}

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3,4-Dimethylhexane-3,4-diol, CHX3​CHX2​−C(OH)(CHX3​)−C(OH)(CHX3​)−CHX2​CHX3​, is heated with dilute acid. Assuming ethyl migrates in preference to methyl, the main product is

Answer: C

More questions on Pinacol-pinacolone and related rearrangements

3,4-Dimethylhexane-3,4-diol, $CH X_{3} CH X_{2} - C (OH) (CH X_{3}) - C (OH) (CH X_{3}) - CH X_{2} CH X_{3}$ , is heated with dilute acid. Assuming ethyl migrates in preference to methyl, the main product is