Study on 5, 15‐dialkylporphyrins interconversion between two conformers in solution

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Abstract
Novel structural features of 5, 15‐dialkylporphyrins in solution are described. The 1H‐NMR spectra of these compounds showed broad signals at room temperature, which split into two sets of signals at lower temperatures. This unusual phenomenon was ascribed to a dynamic interconversion between tow distorted structures. The 5, 15‐dialkylporphyrin has a distorted ring due to the steric hindrance between the 5(or 15)‐alkyl group and the 3, 7(or 13, 17)‐alkyl groups and, depending on the position of the 5, 15‐alkyl groups relative to the average ring plane, can exist in two conformations; syn (where the two alkyl groups are on the same side of the ring plane) and anti (on the opposite sides). Preliminary kinetic study of this interconversion using the NMR line shape analyses is also reported.