Methyl Group Substituent Effect on the Basicity of Meso-Substituted Porphyrins

Methyl Group Substituent Effect on the Basicity of Meso-Substituted Porphyrins

Alvin Sherman Library

Titration studies of three freebase porphyrins (meso-tetra-2-methylphenyl, meso-tetra-3-methylphenyl, meso-tetra-4-methylphenyl) were carried out to determine the corresponding basicity in solution with a nonpolar solvent (toluene). The differences in the porphyrin structure lie within the position of the substituents, specifically the position of the methyl group. In each trial, protonation of the porphyrins was reached through the repeated addition of trifluoroacetic acid (TFA). In examining the protonation of these different isomers, the pKa values were determined through a spectrophotometric analysis. The apparent pKa values were found using the modified Henderson-Hasselbalch equation.