One mole of HBr is added separately to HC –CH_2–CH=CH_2 and to HC –CH=CH_2. In each case, which statement correctly describes the product?

JEE Main Chemistry question

One mole of HBr is added separately to HCC–CH–CH=CH and to HCC–CH=CH. In each case, which statement correctly describes the product?

(A)HBr adds at the triple bond, unchanged
(B)HBr adds at the triple bond, with carbocation rearrangement
(C)HBr adds at the triple bond, at the alternate (non-Markovnikov) carbon
(D)None of the above: HBr adds preferentially at the C=C double bond, not the CC triple bond, in both substratesCorrect

Answer: (D)

Solution

An isolated C=C double bond is more reactive than a CC triple bond toward electrophilic addition, because the alkene's carbons form a more stable (lower-energy) carbocation intermediate than the triple bond's carbons would.

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Question ID VK-142848