Volatile trimethylsilyl derivatives have been a popular choice for vapor phase chromatographic separation of nonvolatile materials. This has led to extensive study of the mass spectra of these derivatives for alcohols,1•2 carboxylic acids,3 and other functional groups.4The mass spectra of functionalized organosilicon compounds per se have only been slightly examined.6 We have observed in the mass spectrum of methyl 4-tri-methylsilylbutyrate6 two novel intramolecular rearrangements involving the silyl center.
The preparation of 4,4-dimethyl-4-silacyclohexadien-l-one, 4,4-dipheny 1-4-silacy clohexadien-l-one, 4,4-dimethyl-4-silacyclohex-2-enone, and 4-trimethylsilyl-3-buten-2-one is reported. The effect of the silyl center on the n -» 7 * transition in their uv spectra is discussed.Brook's discovery of the unusual spectral properties of -silyl ketones stimulated research to determine the mechanism of silicon's effect.2•3 A shift to lower energy in an n -* transition can be produced either by lowering the energy of the excited tt* state or by raising the energy of the ground state. Theoretical molecular
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