摘要：

Ab initio molecular orbital theory is used to study the effects of substitution on the conformations and stabilities of ethyl, propyl, and butyl cations. A separation of the substituent effect into hyperconjugative and inductive contributions is achieved by assuming that the former is conformationally dependent and the latter conformationally independent. The preferred conformation of the cations is determined largely by the relative hyperconjugative abilities of the bonds at the β carbon. The stabilities of the substituted cations depend, in addition, on the inductive effect of the substituent. The theoretical predictions of the relative stabilities of alkyl cations are in reasonable agreement with available gas-phase experimental data.

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