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JEE Advanced levelSingle correct optionDifficulty 3 of 3ap201

2,2-Dimethyloxirane (isobutylene oxide) is treated with a catalytic amount of $BF X_{3}$ in dry ether. The product is

Abutan-2-one
B2-methylprop-2-en-1-ol
C2-methylpropanal
D2-methylpropane-1,2-diol

Answer: C

The Lewis acid opens the epoxide at the tertiary carbon to give

(CH X_{3}) X_{2} C X^{+} - CH X_{2} - O - BF X_{3} X^{-}

. A hydride shift from

CH X_{2}

to the cation (semipinacol type) forms the C=O and gives

(CH X_{3}) X_{2} CH - CHO

.

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