Heterocyclic free radicals. Part 7. Substituent effects on the distribution of spin density in the cation, neutral, and nitroxide radicals of phenothiazine

Abstract

The influence of 2-and 3-substituents in the cation, neutral, and nitroxide radicals of phenothiazine is rationalised in terms of the distribution of spin density between heteroatoms and its response to the electronic effect of the substituents. Mesomeric effects predominate in the cation and neutral radicals but are more important in the former than in the latter. Inductive effects in both families are manifested to a greater extent in the 3-substituted than in the 2-substituted series. In nitroxide radicals, mesomeric effects dominate the 3-substituted series whereas inductive effects dominate the 2-substituted series. Halogen substituents have strikingly different effects in the 3-substituted series of the three families of radicals. This is accounted for in terms of the nature and magnitude of the charge carried by nitrogen in these three radical families.