Inner-Hydrogen Tautomerism in Some 5,15-Unsymmetrically Disubstituted and β-Unsubstituted Porphyrins

概要

論文の詳細を見る
5,15-Unsymmetrically disubstituted and β-unsubstituted porphyrins such as 5-R, 15-(3,5-dimethoxyphenyl) porphyrins [where R=2-benzyloxy-1-naphthyl (1), 2-(2-naphthylmethoxy)-1-naphthyl (2), anthryl (3), or 2,4,6-triphenylphenyl (4)] and 5-(2-benzyloxy-1-naphthyl), 10,15,20-tri(3,5-dimethoxyphenyl) porphyrin (1') were synthesized and studied by ^1H-NMR spectroscopy. At room temperature, 1, 2, 3 and 4 showed doubling of the inner-hydrogen resonances with equal intensities, whereas the pyrrolic βH signals were completely averaged. For 1 and 1', variable-temperature ^1H-NMR experiments were also performed. For 1, the two peaks of the inner hydrogen coalesced at about 313K. In contrast, the pyrrolic βH signals were only slightly broadened even at 213K. On the other hand, 1' showed ordinary singlets of the inner hydrogens at room temperature, and the resonances of both the inner hydrogens and the pyrrolic βH coalesced at about 233K. We interpret these results as indicating the existence of two distinct paths, one slow and the other fast, leading to NH tautomerization in 1. We discuss the structures and energies of cis-tautomers as transition intermediates in relation to the two paths of NH tautomerization.
公益社団法人日本薬学会の論文
2008-07-01