Retention indices and basicity of N1N1-dimethyl-N2-phenylformamidines. ortho-Substituent effect

Abstract

A series of ortho-substituted N¹N¹-dimethyl-N²-phenylformamidines (o-FDMP) have been synthesized and their structure determined by i.r. and ¹H n.m.r. methods. All, except the hydroxy derivative, have the same structure (E). In the case of the hydroxy derivative an intramolecular hydrogen bond appears, and thus two structures Z(20%) and E(80%) are observed in the ¹H n.m.r. spectrum in CDCl₃. The influence of the ortho-substituent on the retention indices, determined on a non-polar column, and on the pK_a values, measured in 95.6% ethanol (azeotrope) and in water is discussed, and compared with those observed for meta- and para-derivatives. The retention indices of the ortho-derivatives, except the hydroxy derivative, obey the same linear correlation as meta-, para-, and other alkyl and aralkyl derivatives. A deviation of the pK_a values of the ortho-derivatives from the linear correlations found for the meta- and para-derivatives are explained by steric effects of the substituent and medium effects.