Conjugation in sulphones. Electronic spectra and polarographic behaviour of thiophen dioxides

The interaction of the sulphone group with an adjacent unsaturated centre has been treated on the basis of HMO theory. The sulphur atom of the SO2 group is assumed to form π-bonds by means of its 3d orbitals. Using the same set of empirical parameters [αS(SO2)=α– 1·4β, α0=α+β, βSO= 0·9β, and βC–SO2= 0·7β], a good correlation has been obtained between the longest-wavelength absorption band and the calculated N→V1 transition energy for 18 sulphones. The energy of the lowest unoccupied molecular orbital shows a good correlation with the polarographic half-wave reduction potential. The SO bond of sulphones is shown to be hardly affected by mesomeric interactions.