D-ORBITAL EFFECTS IN SILICON-SUBSTITUTED PI-ELECTRON SYSTEMS .15. COLOR OF SILYL KETONES

Relative to the colorless dialkyl ketones the n → π* transition energies of the yellow monosilyl and the violet disilyl ketones are considerably lowered. To elucidate the influence of R3Si groups on the carbonyl chromophore, vertical ionization energies, charge-transfer maxima, half-wave reduction potentials, and electronic transitions of alkyl and silyl derivatives of phenyl or naphthyl ketones have been measured and assembled in an approximate experimental MO scheme. The energy differences can be rationalized in terms of both strong inductive effects +ISi > +Ic on the oxygen lone pair no and additional electron back-donation Si ← Cπ. in the excited states, as well as in the ground state. © 1969, American Chemical Society. All rights reserved.