Hydrogen-bond acidity of silanols: A combined experimental and theoretical study

Abstract

The hydrogen-bond (H-bond) donating ability of a series of silanol derivatives has been determined by FTIR spectrometry and complemented by quantum chemistry calculations at the DFT (MPWB1K/6-31+G(d,p)) level. The equilibrium constants of complexation with N-methylpyrrolidinone have been measured in CCl4 solutions. These data expand the pKAHY scale previously covering the field of aliphatic alcohols, phenols and fluorohydrins. Compared to the corresponding alcohol derivatives, the silanol chemical function is found to be a stronger H-bond donor, although the observed frequency shifts, ΔνOH, suggest much greater differences in donor strength than is actually observed. The electrostatic potential descriptor, Vα(r), is successfully used to complete the pKAHY vs. Vα(r) relationship, a helpful methodology to validate the experimental data and to estimate the H-bond acidity of unavailable, unstable, or immiscible compounds.