A number of benzothiazine and phenothiazine derivatives are prepared by reaction of 2- mercaptoaniline and cyclic@-diketo compounds or by reaction of bidentate nucleophiles on 4-chloro-3-nitrocoumarin by using the HSAB principle. The topological resonance energies per*-electron (TREPE's) are calculated for nine benzothiazine and phenothiazine derivatives and correlated with the first reversible peak potentials. The analysis of the data ...