Substituent effects in tautomerism. Part I. Acyl- and sulphonylamidines

Abstract

The tautomerism of acyl- and sulphonyl-amidines is reviewed. The structures of the cations of mobile and fixed forms of acetyl-, benzoyl-, mesyl-, and tosyl-amidines are established by u.v. spectroscopy. Quantitative pK_a measurements demonstrate that the H₂N–CRN–Y form predominates for all series with K_Tca. 30 for the acyl- and ca. 10⁷ for the sulphonyl compounds.

These results are compared with the tautomerism of 2-acylamino- and 2-sulphonamido-pyridines, and differences in tautomeric behaviour are rationalised.