Tautomerism in 2-Substituted 5,10,15,20-Tetraphenylporphyrins

Article abstract of DOI:10.1021/ja00273a010

β-Substitution of 5,10,15,20-tetraphenylporphyrin alters the position of the tautomeric equilibrium 2a <*> 2b, which can be observed by high-field variable-temperature NMR spectroscopy.When R= NO2, CHO, Cl, Br, OMe, CN, NHCOMe,SPh, OCOPh, or OH the dominant tautomer is 2a, where R lies on the isolated double bond, while when R= CH=CH2, CH2OH, NH2, Me, CH(Me)2, or (CH2)3Me the major tautomer is 2b, where R lies on the aromatic delocalization pathway.These substituent effects do not follow a know scale.