Transmission of electronic effects in organosilanols

Abstract

The effectiveness of the silicon atom in transmitting electronic effects in a series of substituted diphenylsilanediols, dialkylsilanediols, and poly(diorganosiloxane)-αω-diols has been shown by an i.r. spectroscopy study to be high. The acidities of the diorganosilanediols give an approximately linear correlation with Σ_σ* values, while the protondonating properties of the substituted diphenylsilanediols fall in the order m-CF₃ > m-Cl > p-Cl > p-F > o-Me > H > m-Me > p-Me > p-MeO > p-Me₂N. In accord with alkylbenzoic acids, the ortho-isomer of ditolysilanediol is the most acidic and this has likewise been attributed to steric inhibition of resonance. The acidities of the halogenodiphenylsilanediols have been interpreted in terms of contributions from resonance structures and related to thermal condensation data. Enthalpy values for the interaction of phenol with the poly(diorganosiloxane)-αω-diols have been calculated and the changes in basicity have been interpreted in terms of multicentre π-bonding in the siloxane chain. A number of the para-substituted diphenylsilanediols appear to be dimorphous.