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Here we have three isomers of butene there structure of who I have attached:

  1. cis-butene
  2. trans-butene
  3. iso-butene
    enter image description here

I was able to figure out that the trans isomer would obviously be more stable than the cis one due to steric repulsions among the methyl groups in the cis isomer. But how would we judge the isobutene? As they are isomers, the number of hyperconjugative structures ends up being the same.

I had an intuition that this might relate to intermediate stability in hyperconjugation but couldn't come to any conclusions.

Prajwal Tiwari
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  • You might want to start with experimental results like heats of formation and then rationalize the results. – user55119 Mar 18 '21 at 15:39
  • @user55119 yes but that would just tell us the order and would just be a raw answer. How can we understand how iso-butene is the most stable? – Prajwal Tiwari Mar 18 '21 at 15:59
  • If you argue for hyperconjugation, then two methyl groups on the same sp2 carbon is better than on different sp2 carbons. – user55119 Mar 18 '21 at 16:09
  • @user55119 Oh so we're indeed looking at the intermediate carbocation that will be formed during formation of the hyperconjugative structure as it would be stabilised by the positive inductive effect by the methyl groups right? – Prajwal Tiwari Mar 18 '21 at 16:13

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