Tautomerism of substituted 2H-1,2,6-thiadiazin-3-one 1,1-dioxides: 1H, 13C, and 15N nuclear magnetic resonance studies

Abstract

Tautomerism of 2,5-disubstituted (4), 4,5,6-substituted (5), and 5-substituted 2H-1,2,6-thiadiazin-3-one 1,1-dioxides (6) has been studied by u.v., ¹H, ¹³C and natural-abundance ¹⁵N n.m.r. spectroscopies. The effect of solvent concentration, temperature, and the nature of the substituents on the K_T variation has been investigated. Comparison between the tautomeric behaviour of 2H-1,2,6-thiadiazin-3-one derivatives and the related pyrazol-5-ones provides some conclusions about the role of aromaticity on the stability of the different tautomers.