Interaction between the carbonyl group and a sulphur atom. Part 9. The relationship between conformation and ground- and excited-state interactions in some α-sulphur-substituted cycloalkanones

Abstract

The conformations of some α-sulphur-substituted cycloalkanones are estimated approximately from the i.r. spectra. The decrease of the carbonyl stretching frequency in these compounds, by comparison with the corresponding unsubstituted ketones (Δν_CO), is reported and interpreted as due to hyperconjugative σC(2)–S–π_CO interaction on the basis of the dependence on the position of C(2)–S bond. Similarly, hyperconjugative interaction in the excited state is proposed to account for the bathochromic shift of the n→π* band, at 300 nm, of the same compounds. The shorter wavelength u.v. absorption band, at 250 nm, is assigned to charge transfer from sulphur to the carbonyl group owing to its dependence on the position of the 3_p orbital of sulphur relative to the carbonyl group.