NMR Studies of 2-Aryl Derivatives of Benzimidazole, Benzimidazolium Ion, and Benzimidazoline

A series of 2-arylbenzimidazoles, 2-aryl-1,3-dimethylbenzimidazolium iodides, and 2-aryl-1,3-dimethylbenzimidazolines were prepared and their NMR spectra were examined. The substituent parameters were calculated for 2-benzimidazolyl, 2-benzimidazoliumyl, and 2-benzimidazolinyl groups on the chemical shifts of the protons and the carbons of benzene ring. The 2-benzimidazoliumyl group was found to cause a significant up-field shift of the ipso-carbon signal and down-field shift for the ortho- and para-carbon signals. On the other hand, the 2-benzimidazolyl and the 2-benzimidazolinyl groups cause down-field shift of the ipso-carbon signals but cause almost negligible change on the other carbon signals.