Notes. Substituent effects on enthalpy and entropy for the axial ligation of zinc tetraphenylporphyrinates

Abstract

Thermodynamic data were determined for the axial ligation of zinc tetra(substituted phenyl)porphyrinates by 1-methylimidazole in toluene. The data are used to (1) verify the isoequilibrium condition for the reaction and (2) determine the effect of the substituent on the enthalpy and entropy of reaction. Among para-substituted derivatives, the enthalpy exhibits no observable trend as the electron-donating–withdrawing ability of the substituents is varied. Relatively large entropy losses are associated with the presence of electron-donating para substituents.