A substituent correlation and medium effects on the annular tautomerism of substituted 5-aryltetrazoles: the nitrogen analogues of benzoic acids. A carbon-13 n.m.r. and dipole moment study

The annular tautomerism of substituted 5-phenyltetrazoles shows a linear correlation of log KT{KT=[N(1)H]/[N(2)H]} with the Hammett σ values of para-substituents. The tautomerism favours the 1H-form but electron-withdrawing substituents displace the equiliblium towards the 2H-form. Solvent dielectric permittivity and temperature effects also influence the annular tautomerism. A change of solvent from dimethyl sulphoxide to dioxane and an increase in temperature had similar effects in orienting the tautomerism towards the 2H-form, but the temperature effect was relatively small. Carbon-13 n.m.r. shifts and dipole moment analyses of the tautomerism gave complementary results.