According to me, the answer is B as the tertiary allylic carbocation should be more stable. But the answer given is D and in the given solution, the tertiary allylic carbocation rearranges to primary allylic carbocation to yield Option D.

My question is why does rearrangement from tertiary allylic carbocation to primary allylic carbocation take place?

Source: JEE Advanced 2015 Paper 1 Q31


marked as duplicate by Mithoron, Nilay Ghosh, pentavalentcarbon, Tyberius, Jon Custer May 17 '18 at 17:54

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  • $\begingroup$ have you hearrd about 1,2 addition and 1,4 addition in conj dienes $\endgroup$ – amish dua May 15 '18 at 4:57
  • $\begingroup$ youtube.com/watch?v=JcvQXSm341A this might be helpfull $\endgroup$ – amish dua May 15 '18 at 4:59
  • $\begingroup$ Steric hindrance in the Br attack step, maybe? $\endgroup$ – Oscar Lanzi May 15 '18 at 9:05

The carbocation will be formed as per stability rules but as it is conjugated system the cabocation resonates and as the less stable carbocation is more reactive it is attacked by Br-


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