What's the major product of the dehydration reaction of 2,3-dimethyl-2-phenylbutan-1-ol with conc. $\ce{H2SO4}$ (at high temperature)?

I am aware that in this reaction $\mathrm{E}$1 mechanism will be followed, and I'm getting 2-methyl-3-phenylpent-2-ene as the answer whereas the answer given in my book is 4-methyl-2-phenylpent-2-ene!

The procedure which I followed is depicted in following scheme:

The procedure which I followed

Help me to find out my mistake here.

  • 1
    $\begingroup$ Please edit your post for grammar, punctuation, and capitalization; and use MathJax for typesetting. $\endgroup$ Jul 2, 2021 at 18:55
  • 5
    $\begingroup$ What's to explain? My answer is identical with my answer. How am I to explain why your answer (which I don't know) is different from the answer in your book (which I don't know either)? $\endgroup$ Jul 2, 2021 at 19:26
  • $\begingroup$ Post your work and how you got your answer. Otherwise, this would be closed as a homework question in few minutes. $\endgroup$ Jul 3, 2021 at 0:49
  • $\begingroup$ Does your book gives 2,3-dimethyl-1-phenylbut-1-ene as the answer, for curiocity? $\endgroup$ Jul 3, 2021 at 0:54
  • 3
    $\begingroup$ @TRC: Yes, I'd say so. In addition, phenyl is known for great neighboring group participation, which would be great possibility here to reduce high energy of primary carbocation. $\endgroup$ Jul 3, 2021 at 14:52

1 Answer 1


This might be the mechanism based on the answer in your book. The isopropyl group might shift because of the resonance stabilization due to phenyl group and inductive effect of the methyl group in the resulting carbocation. This carbocation might be the most stable one compared to the other carbocations' possible.

  • 8
    $\begingroup$ The issue appears to boil down to whether the isopropyl group migrates, or whether the methyl group migrates. Why should iPr migrate over Me? "Because it gives the book's answer" is not really satisfying enough. $\endgroup$ Jul 3, 2021 at 12:59
  • $\begingroup$ @orthocresol True - I always knew phenyl group to have greater migratory aptitude than alkyl groups... $\endgroup$
    – TRC
    Jul 3, 2021 at 14:12
  • $\begingroup$ @cva You are correct! I checked other possibilities as well and found that this carbocation is the most stable among all (having not only resonance stabilization and inductive effect but also the maximum number of alpha-Hydrogen atoms available for hyperconjugation) and that's why it gives the major product. Thanks $\endgroup$
    – Aspirant
    Jul 3, 2021 at 18:42
  • $\begingroup$ Agree with @orthocresol .Further , what is the book & author ? $\endgroup$ Jul 4, 2021 at 4:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.