The carbonyl group frequency. Part IV. Aliphatic aldehydes

Abstract

The carbonyl frequencies for vapours and solutions of a series of simple alkyl aldehydes have been recorded. The variation in frequency with substitution is less regular than with the corresponding ketones and the variation with solvent requires the operation of a specific interaction which is identified with the nucleophilic properties of the solvent. Application of simple vibrational models to the analysis of the change in the carbonyl group frequency between acetone and acetaldehyde indicates that changes in mass and geometry, in the carbonyl force constant, and in the symmetry of the vibration can individually all produce substantial effects; the overall small change in frequency arises from the cancellation of these effects.