Hydrogen Bonding and the n → π Blue Shift in α,β-Unsaturated Ketones

Abstract

The c.d. spectra of α,β-unsaturated ketones through the n → π* absorption region are, in general, better resolved than the corresponding ultraviolet spectra and are free of overlap from neighbouring transitions. In consequence, the nature of the solvent-induced blue shift is more clearly discernible in circular dichroism. That part of the blue shift which is ascribable to hydrogen bonding is shown to result from a redistribution of intensity between vibrational sub-bands rather than a change in energy of the n → π* band as a whole.