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We know that if a structure has all equivalent resonance structures, then it will be highly stabilised. So then why benzylic carbocation is more stable than other cyclic allylic carbocations, though allylic carbocation has all equivalent resonance structures?

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  • $\begingroup$ For example you want to know why benzylic carbocation is more stable than cyclohexen carbocation? $\endgroup$ – ParaH2 Nov 9 '15 at 19:19
  • $\begingroup$ Do you know that the more you find mesomer forms the more the stability is? Do you want a proof? $\endgroup$ – ParaH2 Nov 9 '15 at 19:52
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More the number of resonance structures (alias mesomers) more is the stability of the carbocation so benzylic carbocation with 4 mesomers is more stable than 2 structures of the allylic carbocation.

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    $\begingroup$ -1: While this explanation is indeed correct in the case of benzylic and allylic cations, it is, in general, not correct (see: acetate, 2 resonance forms vs phenoxide, 4 resonance forms) and I cannot agree with the answer which strongly implies that it can be generalised to all systems. $\endgroup$ – orthocresol Dec 19 '15 at 9:02

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