The deuteriation of the rneso-positions of octaethylporphyrin has been observed in dideuteriosulphuric acid. The n.m.r. spectra of this porphyrin and the related chlorin and a-tetrahydroporphyrin are discussed and are employed to evaluate rates of meso-deuteriation in trifluoroacetic [2H]acid. The rates increase in the sequence : porphyrin < chlorin U P < chlorin r8 < a-tetrahydroporphyrin pS < a-tetrahydroporphyrin y. The interpretation of these results is discussed.
f D. M. G. M. and G. F. S. were holders of a Science Research Council research studentship and research fellowship, respectively.X To whom enquiries should be addressed.
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