For the above reaction I am asked to predict $\ce{X}$, the major product.

Of the options given, I thought product (1) would be correct, seeing as how it has the most stable intermediate cation (tertiary) and a highly substituted double bond.


The answer however states that product (2) is the major product.

I can't understand why the second product would be favored over the first. There's no obvious stabilizing factor here in product (2).

  • $\begingroup$ Oxonium cations are more stable than tertiary. $\endgroup$
    – Mithoron
    Commented May 4, 2016 at 23:15
  • $\begingroup$ Isn't a secondary carbocation the intermediate and not an oxonium ion for product 2?I mean, after N2 is eliminated and a hydride transer occurs from the carbonyl carbon to the carbocation, isnt a secondary carbocation formed next to electronegative oxygen? $\endgroup$ Commented May 4, 2016 at 23:35
  • 4
    $\begingroup$ ...Which is a protonated carbonyl - oxonium cation. Somehow this powerful mesomeric stabilisation is often omitted $\endgroup$
    – Mithoron
    Commented May 4, 2016 at 23:43
  • $\begingroup$ (2) cannot be the major product as of the images you are supplying now unless a carbon source is added. The carbon atoms don’t add up. $\endgroup$
    – Jan
    Commented May 5, 2016 at 12:05

1 Answer 1


I think (2) is correct, but either your or your book erred in writing it. This is what the mechanism (and major product) should be:



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