The major product of the following reaction is: CH_3CH(Br)CH_2CH(Br)CH_2CH_3 with KOH/CH_3OH , heat.

JEE Main 2017 Chemistry question

The major product of the following reaction is: with , heat.

(1)\mathrm{CH_3CH{=}CH{-}CH{=}CHCH_3}Correct
(2)\mathrm{CH_2{=}CHCH{=}CHCH_2CH_3}
(3)\mathrm{CH_3CH{=}C{=}CHCH_2CH_3}
(4)\mathrm{CH_2{=}CHCH_2CH{=}CHCH_3}

Answer: (1)

Solution

Alcoholic KOH with heat is the classic reagent for **E2 dehydrohalogenation**, and with two bromine atoms the reaction occurs twice to give a diene. Number the chain:

\mathrm{-----}.

Each elimination can go towards either neighbour, but Zaitsev's rule directs the base to give the

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Question ID VK-115817