Abstract The formation constants of the complexes formed between seven protonated N- bases and imidazole (Im) and imidazolium cation with twelve N-bases and the acidic dissociation K AN a (BH+) have been determined in acetonitrile AN. There exists a correlation between the pK AN a (acceptor)− pK AN a (donor) that form the heteroconjugated complexes. The experimental formation constants of the complexes,( ...