Proton NMR studies of reduced porphyrin compounds

Abstract

AbstractDetailed 1H NMR studies of ms tetraphenylchlorins (H2TPC), new amino‐ and hydroxypyrroline substituted ms tetraphenylchlorins and ms tetraphenylisobacteriochlorins (H2TPisoB) are presented and discussed. The results obtained are consistent with the general aspects of the ring current models as applied to the parent porphyrins. According to proton chemical shifts a gradual reduction in the magnitude of the ring current is observed in the order ms tetraphenylporphyrin (H2TPP) > H2TPC> ms tetraphenylbacteriochlorin (H2TPB) > H2TPisoB. The 1H NMR spectra show chemical non‐equivalence of the pyrroline ring protons due to adjacent substituents, and effects of steric constraints on the aminoalkyl substituents due to the close vicinity to the meso phenyl rings. The non‐equivalence of the methylene protons of the pyrroline ring produces geminal coupling between the two methylene protons and vicinal coupling with the adjacent pyrroline proton, more pronounced in H2TPCOH and in . Restricted configuration of the methylene groups in the ethyl groups of H2TPCC(H)(CH3)N(CH2CH3)2 produces observable geminal coupling between the methylene protons. 1H NMR reveals the difference between two types of meso phenyls in the chlorins, and three types of meso phenyls in isobacteriochlorins, as reflected in the chemical shifts of the o‐phenyl protons.