# Which of the following carbocations is more stable?

Which of the following carbocations is more stable?

I know two major factors in determining carbocation stability: resonance and the number of carbon atoms neighboring the positive carbon. Does the double bond in the substituent of the first molecule participate in resonance?

• The one with the aliphatic C=C bond may be more stable since there may neighbouring group participation, allowing dispersal of positive charge – Tan Yong Boon Oct 17 '19 at 6:23
• @TanYongBoon There is an $\mathrm{sp^3}$ carbon in-between which breaks resonance so the shorter chain allows for more hyperconjugation. – Jan Oct 17 '19 at 6:39
• @Jan I am not talking about resonance. When I mean "neighbouring group participation", I am referring to the $\pi$ electron density being donated directly to the positively charged carbon atom, forming a cyclopropyl or cyclobutyl structure – Tan Yong Boon Oct 17 '19 at 6:54
• @TanYongBoon Oh, I think I see what you mean; analogous to a metal-ethene complex? If that’s the case, I’m not sure whether the single $\ce{CH2}$ group provides enough flexibility but I would have to build a model. – Jan Oct 17 '19 at 6:56
• @TanYongBoon that mechanism would require a "six membered ring". In term or charge stabilisation/relative stability the smaller carbocation should be favoured. – Alchimista Oct 17 '19 at 9:45