Spectral Characteristics of Acylsilanes

The spectra of a series of aliphatic and aromatic acylsilanes were recorded using ir, uv, 1H, 13C, and 29Si nmr techniques. The spectra of analogous ketones and an amide and phosphamide were also recorded to permit direct comparison. The silanes consistently exibited a downfield shift of 30 ppm for the 13C nmr carbonyl resonances relative to their all-carbon analogs. Similarly, the phosphamide carbonyl resonance showed a 40 ppm downfield shift relative to the corresponding amide. These results are interpreted as indicating multiple bond character in the Si-CO and P-CO bonds.