Theoretical gas-phase stabilities of α-trimethylsilyl-substituted tertiary carbenium ions

Theoretical hydride ion affinities in the gas phase are presented for alpha-SiMe3-substituted tertiary carbenium ions. Thermodynamic stabilization of the "nascent" ions by a single trimethylsilyl group is weaker than by a tert-butyl group but comparable to the effect of a methyl group. In the case of the cyclopropenylium cation, the stabilization by a trimethylsilyl group even exceeds the effectiveness of a tertbutyl group. Compliance constants are used to quantify the chemical concept of hyperconjugation. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.