A study of annular tautomerism, interannular conjugation, and methylation reactions of ortho-substituted-5-aryltetrazoles using carbon-13 and hydrogen-1 n.m.r. Spectroscopy

Abstract

In ortho-substituted-5-phenyltetrazoles, Ar^–CN₄H (Ar = 2′-MeC₆H₄, 2′-ClC₆H₄, or 2′,6′-Cl₂C₆H₃), the rings are twisted out of the planar configuration and interannular conjugation is inhibited. In each case the tetrazole 1-NH tautomêr is strongly predominant. When the rings are coplanar, as in para-substituted-5-phenyltetrazoles, the electron-withdrawing effect of the para-substituents changes the tautomerism significantly back towards the 2-NH form. Methylation of the anion of 5-(ortho-substituted-phenyl)tetrazoles occurred equally at the 1-N- and 2-N-positions, or slightly favoured the 1-N-position, and thereby contrasted with the p-substituted derivatives, where 2-N-methylation strongly predominates.