PROTON AFFINITIES AND GAS-PHASE BASICITIES OF ALKYL AND SILYL ETHERS

The absolute proton affinities and gas-phase basicities for a series of related alkyl and silyl ethers, (SiH3)2O, H3SiOCH3, (CH3)2O, H3SiOSiH2CH3, H3COSiH2CH3, H3SiOC2H5, H3COC2H5, H3SiOC(CH3)3, H3COSi(CH3)3, and H3COC(CH3)3, have been computed via ab initio molecular orbital calculations. Geometry optimizations were carried out at the Hartree-Fock level with the 3-21G and 6-31G(d) basis sets, and correlation energies were computed with second- and third-order Moller-Plesset theory. Vibrational energy changes were also included from 3-21G calculations. It is found that the range of proton affinities spans from 187 to 205 kcal mol-1. Comparisons with available experimental data indicate that the predicted thermodynamic results are accurate to within 3 kcal mol-1. The low gas-phase basicity of disiloxanes is confirmed, while the similar results for dialkyl ethers and analogous alkyl sily ethers are particularly notable. The structures of the protonated molecules are also characterized in detail.