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What is the order of stability of the cycloalkyl carbocations?

I think the stability should increase as we move from cyclopropyl carbocation to cyclohexyl carbocation, since the angle strain is continuously decreasing. I understand this as, the difference between the stable 120 degree angle of a carbocation and the actual bond angle of the cycloalkyl cation is decreasing on moving from cyclopropyl to cyclohexyl carbocation.

But someone recently told me that the cyclopentyl carbocation is more stable than the cyclohexyl carbocation, citing the faster rate of SN1 reaction observed in 1-chloro-1-methylcyclopentane than in 1-chloro-1-methylcyclohexane.

So what is the actual stability order of these cations?

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  • $\begingroup$ Stability and reactivity are relative concepts and they are both rely on reference frames. The both are not linked and one cannot infer from one to the other. Sometimes these arguments seem reasonable, and it has been done before, but usually this is coincidental. Your friend might be right, but that doesn't mean you're wrong. The relative stability of carbocations is no easy feat to determine, and there might not be a suitable textbook concept yet. In any case, you need to find a common reference frame for both ions. $\endgroup$ Feb 13 at 0:26

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