The effects of substitution, lanthanide-shift reagents, solvent changes, and tautomerism were investigated on ^(13)C chemical shifts of pyrrole, pyrazole, imidazole, s- and v-triazole, and tetrazole. It was concluded that ^(13)C chemical shifts are of limited value to ascertain the positions of tautomeric equilibrium for rapidly interconverting azole tautomers.
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Elguero et al. (1974) studied this question.