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Amidines. Part 32. Influence of Substitution at the Amino Nitrogen Atom on the Sensitivity to Substitution at the Imino Nitrogen Atom. pKa Values of N1-Methyl-N1-phenylformamidines in Water-Ethanol Solutions
Oszczapowicz, Janusz,Kuminska, Mariola
, p. 103 - 108 (2007/10/02)
A series of new N1-methyl-N1-phenylformamidines (RN=CH-NMeC6H5, 13 compounds) containing variable substituents at the imino nitrogen atom has been synthesized.The pKa values of the compounds have been measured in four binary ethanol-water solvents and correlated with Hammett-type substituent constants, and with pKa values of the corresponding primary amines determined in the same solvents.It is shown that substitution at the amino nitrogen atom has considerable influence on the sensitivity of the amidino group to the polar effects of substituents at the iminonitrogen atom.The parameters for both types of regression depend on the solvent.The equation for prediction of the pKa values for trisubstituted amidines, enabling explanation of changes in the ρ values for substitution at one site caused by substitution at the other two sites, is derived.
