The influence of the size and position of the alkyl groups in alkylimidazole molecules on their acid-base properties

Dissociation constants of HL+ acids, where L stands for 1-alkylimidazole, 1-alkyl-2-methylimidazole, 1-alkyl-2-ethylimidazole, 1-alkyl-2-propylimidazole, 1-alkyl-4-methylimidazole and 1-alkyl-2-ethyl-4-methylimidazole, were determined potentiometrically. For each of the homologous series of these bases, a relationship has been derived between the pK(a) value and the number of carbon atoms in the hydrocarbon group for (CH2)(n)less than or equal to13. The basicity of the alkylimidazoles has been found to increase linearly with increasing carbon chain length. The slopes of straight plots of pK(a)= f(n(CH2)) have been found to increase with increasing basicity of homologous series of the alkylimidazoles.