In the 3,4-dihydropyran shown below will the oxygen or the pi electrons of the double bond attack the hydrogen cation during hydrolysis and why?

This is my attempt towards a solution: The oxygen lone pair clearly can attack the hydrogen cation better than the pi electrons being a better a nucleophile, but according to my textbook (T.W.Grahams Solomons) the pi electrons of the double bond attacks, but shouldn't the oxygen atom be a better nucleophile than the pi electrons?



The functional group in question is a vinyl ether, and it is a mistake to consider these groups as isolated. The oxygen is in conjugation with the vinyl group, meaning that resonance favors the entire system attacking. There is no way to leverage conjugation as an energetic driving force if the oxygen attacks by itself.enter image description here

  • $\begingroup$ Could you please rephrase your last sentence? I didn't really get it. $\endgroup$ – Karan Singh Feb 17 '16 at 7:18
  • $\begingroup$ If you protonate the oxygen, you are not really using a conjugated system any more, and the energy gain from conjugation is not helpful for driving the reaction $\endgroup$ – Lighthart Feb 17 '16 at 19:05

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