Stereochemical and electronic structure of the free base,cation, and dication of porphin

The equilibrium stereochemical and electronic structure of the free base and the mono- and dications of porphin was calculated by the MO-LCAO SCF method in the CNDO/2 approximation. Successive protonation of the porphin molecule leads to an increase in the dimensions of the conjugation contour and to stage-by-stage exclusion of the nitrogen atoms. It was also established that single and double protonation of the free base does not lead to destruction of the coplanarity of the porphyrin macrocycle.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 339–343, May–June, 1988.