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How can the stabilities of the tropylium and cyclopropenyl carbocations be compared?

Structures of carbocations

Both are aromatic according to Hückel's rule. I think that to compare the stabilities, we must either count the number of resonance structures, or perhaps we could say that cyclopropenyl is less stable due to angle strain. Am I on the right track?

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Both ions are indeed strongly stabilized by aromatic coupling, and salts containing both ions are known. But, of course, aromaticity is not the only thing that determines stability. Tropylium ion, with its lesser ring strain and more atoms over which to distribute the positive charge, forms ionic salts with more anions (e.g., ionic $\ce{C_7H_7Br}$ versis covalent $\ce{C_3H_3Br}$) and in that sense is more stable.

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  • $\begingroup$ I am interested in the same question but if you could evaluate or give some reference to it then it would be more helpful. $\endgroup$ – user187604 Dec 6 '18 at 10:11

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