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When a benzylic carbocation (-CH2+) is attached to a phenol ring, at which position does the resulting cation gain the greatest stabilisation from the -OH group?

1. para (p-) CH2+ substituted phenol
2. ortho (o-) CH2+ substituted phenol
3. meta (m-) CH2+ substituted phenol
4. None of these

Correct answer: para (p-) CH2+ substituted phenol

Solution

The lone pair on the phenolic oxygen can delocalise onto the benzylic carbon only when the +CH2 is at ortho or para. The para arrangement gives the most stable, less sterically strained oxocarbenium-type resonance structure, so the para cation is most stable.

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