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JEE Advanced levelSingle correct optionDifficulty 3 of 3hc127

Propyne is treated with $NaNH X_{2}$ in liquid ammonia, then ethanal is added, and the mixture is finally treated with aqueous acid. The product is

A2-methylbut-3-yn-2-ol
Bpentan-2-one
Cpent-4-yn-2-ol
Dpent-3-yn-2-ol

Answer: D

The acetylide

CH X_{3} - C \equiv C X^{-}

adds to the carbonyl carbon of

CH X_{3} CHO

, giving an alkoxide that is protonated on work-up:

CH X_{3} - C \equiv C - CH (OH) - CH X_{3}

. Numbering from the carbon bearing OH gives pent-3-yn-2-ol.

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