Raman spectroscopy and DFT calculations of intermediates in the hydrolysis of methylmethoxysilanes

A series of methylmethoxysilanes (tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, and trimethylmethoxysilane) underwent hydrolysis and condensation in aqueous solutions at circum-neutral pH while the reaction was monitored by Raman spectroscopy. The SiO and SiC stretches of the silanes were vibrationally coupled so that a single intense peak was observed in that region of the Raman spectra. The SiO/SiC stretch was assigned for all of the solvated reactants and silanol intermediates and products of each hydroysis step in solutions of low ionic strength and neutral pH. Assignments compared favorably with vibrational frequencies calculated by a DFT method.