Quaternary salts of quinolybenzimidazoles

The nitrogen atoms of the benzimidazole ring are alkylated initially in the quaternization of 2-(2-quinolyl)benzimidazole, and the nitrogen atom of the quinoline ring is alkylated only after this. Pyridyl- and quinolylbenzimidazoles and their quaternary salts were synthesized in order to study geometrical isomerism in the dihetaryl series. It was concluded that geometrical isomerism cannot occur in the case of the protonated forms or any other quaternary salts of dihetaryls, since as a result of the mutual electron-acceptor effect of the heteroaromatic cations the carbon-carbon bond between them is converted to a single σ bond, despite the fact that it is a bond between two sp2 carbon atoms.