Thiopyrones, Dithiolones, and Derivatives

Thiopyrones, Dithiolones, and Derivatives. The iso-ir-electronic tropones and thiotropones (92)—(99) have stimulated much theoretical interest. Although the electronic spectra of the six-membered rings and derivatives 

CNDO/S calculations are in agreement with the observation that protonation of (98) leads to the disappearance of the tt n absorption and to a shift of the it it absorptions to lower wavelengths. The basicities of (92) and (93) and condensed systems have been studied within the 7T -approximation. 

Using only the p-model of sulphur, PPP-type calculations of the meso-ionic structures (100)—(102) have given an adequate description of the spectral data an explanation was also given for the deeper colour of phenyl-substituted (101) and (102) relative to the isomeric structures. An analysis of the population of the d-orbital as well as the bond energies of (101) indicated no higher d-participation than in (87). 

Inserting one double bond between the ring and the C=0 (C=S) group leads to (103), with a non-bond interaction between the S and 0(S) atoms. These compounds are considered below. 

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