Substituent stabilisation energies in α-substituted carbocations CH2Z+, CH3CHZ+ and (CH3)2CZ+ where Z is NH2, PH2, AsH2, OH, SH and SeH

Add time:09/26/2019    Source:sciencedirect.com

Ab initio molecular orbital calculations at the MINI 1 and 3–21G levels of theory have been used to optimise structures for α-substituted carbocations CH2Z+, CH3CHZ+, and (CH3)2 CZ+, and for the hydrocarbons CH3Z, CH3CH2Z and (CH3)2 CHZ where Z is NH2, PH2, AsH2, OH, SH and SeH. Energy differences between conformers as calculated by theory are compared with experimental results. Substituent stabilisation energies, calculated by using isodesmic reactions, are largest in primary ions and smallest in tertiary ions. For elements from Group V the stabilising effect of an α-substituent is NH2 > PH2 > AsH2 and for Group VI OH > SeH > SH. There is a good correlation between experimental and calculated values for the effect of methyl substitution on the hydride affinities of substituted methyl cations.

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