Cross-polarization magic-angle-spinning silicon-29 nuclear magnetic resonance study of silica gel using trimethylsilane bonding as a probe of surface geometry and reactivity

/sup 29/Si NMR experiments, using cross polarization (CP) and magic-angle spinning (MAS), were carried out on a variety of silica gels and the products of their trimethylsilylation reactions with the silylating agent, hexamethyldisilazane (HMDS). A methodology has been developed to provide quantitative relationships on structure and reactivity from the /sup 29/Si CP/MAS spectra. Geminal-hydroxyl silanol sites were found to be more reactive to HMDS than lone-hydroxyl silanol sites. Measured surface hydroxyl densities and trimethylsilane coverages are discussed in terms of structural models.