Mesoionic compounds with a bridge nitrogen atom. 11. π-Electron structures and absorption spectra of aza analogs of thiazolo[3,2-a]pyridinium 3-oxide

Abstract

The π-electron structures and energies of the first electronic transitions of a number of mesoionic thiazoloazinium oxides were calculated by the Pariser-Parr-Pople method. An analysis of the data obtained showed that in the case of annelation of the heterorings and the introduction of a phenyl group in the 2 position the first absorption band should be shifted bathochromically, in agreement with the experimental data. In the case of replacement of the methylidyne groups by a trivalent nitrogen atom, however, one should have expected both bathochromic and hypsochromic effects, depending on the position into which the nitrogen atom was introduced. However, it was found experimentally that the first band is shifted to the long-wave region in all cases.