The NMR spectra of porphyrins. 27—proton NMR spectra of chlorophyll‐a and pheophytin‐a

The 500 MHz proton NMR spectra of chlorophyll‐ a in several non‐aggregating solvents, at high dilution, are given and that of pheophytin‐ a in CDCl 3 at 360 MHz and at high dilution is reported. Under these conditions, the dispersion is such that separate resonances are observed and can be assigned for all protons in the molecules, except P‐5 to P‐15 in phytyl side‐chain. The complex spin systems of the C‐7 propionic ester side‐chains, and of the P‐1/P‐2 fragment, are analysed and the couplings obtained are interpreted in terms of possible conformations of the side‐chain.