Energies of Association of Carbenium and Silylium Cations with Oxygen-Containing Molecules

摘要

The energies of association of Me_nH_(3_n)X~+ cations (n = 0-3) with molecules of oxygen-containing bases (water,methanol,dimethyl ether) were calculated by the B3LYP/6-31G(d) method.These energies decrease with an increase in the number n of methyl groups at the X atom;this trend is more pronounced for X = C,which is due to a lower degree of charge transfer in the cation from the occupied orbitals of the methyl group to the vacant orbital of X in the case of X = Si.An increase in the association energy with an increase in the number of methyl substituents at the oxygen atom is due to an increase in the energy level of lone electron pairs of oxygen upon methyl substitution.As a result,the energy gap between the electronic levels of the unoccupied orbital of the cation and orbitals of the oxygen lone electron pairs becomes narrower,which makes the interaction between the unoccupied and occupied orbitals more efficient.