NMR Spectra of Porphyrins. 29. Conformation of the Propionic Ester Side Chain in Chlorophyll Derivatives

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The 360- and 500-MHz proton NMR spectra of the five nonequivalent protons in the C-7 propionic ester side chain of various chlorophyll derivatives have been completely analyzed in order to investigate the effect of structural variations in the chlorophyll nucleus on the side-chain conformation in solution. Analysis of the coupling constants and chemical shifts obtained shows that introduction of a central nickel atom into the chlorophyll nucleus causes profound variations in the side-chain conformation, presumably reflecting conformational changes in ring D. Less marked, but similar, effects occur upon opening of the exocyclic ring. In contrast, the introduction of δ substituents results in different, more localized, deformations, while introduction of a central magnesium atom causes little change in side-chain conformation. © 1987, American Chemical Society. All rights reserved.

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Journal of Organic Chemistry

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