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