On the basis of the stable structures of reactants and products, transfer reactions of inner hydrogen atoms in protonated di-oxa- or thia-porphyrin were studied. The transition states were found and optimized, and the differences between rates of inner hydrogen atom transfer (IHAT) reactions were presented. The calculated results show that the main foctors to affect the relative stability of conformations of the studied protonated molecular systems are aromaticity, the steric hindrance and the electrostatic interaction. The rate differences of IHAT reactions in these protonated double-substitution systems are remarkable. The IHAT reaction rate differences of inner ring substitution mainly resulted from electronic effects rather than conformational changes. In addition, the di-substitutional effects on the IHAT reaction rates are greatly larger than the mono-substitutional effects.

Key words: porphyrin, transition state, structural change, inner hydrogen atom transfer