Conformational studies of α-substituted carbonyl compounds. Part 1. Conformation and electronic interaction in hetero-substituted acetones by infrared and ultraviolet spectroscopy

Abstract

ν_CO Frequencies and intensities and n→π* transition energies were measured for some heterosubstituted ketones (XCH₂COMe : X = F, Cl, Br, I, NMe₂, OMe, SMe, or SEt) and compared with the corresponding unsubstituted ketone. The stability of the gauche-conformers is discussed in terms of hyperconjugative interactions between σ_{C – X} and π_CO orbitals and repulsive interactions between CO and C – X dipoles. The carbonyl frequency shifts, induced by inductive (Δν_I), field (Δν_F), and hyperconjugative effects (Δν_H), are estimated separately. A close relationship is shown to exist between the Δν_H values and the energies of the n→π* transition.