SPECTROSCOPIC AND QUANTUM CHEMICAL STUDY OF THE PROPERTIES AND STRUCTURE OF 5-HYDROXYBENZIMIDAZOLE

The MNDO method has been used to calculate the heats of formation of six tautomeric forms of 5-hydroxybenzimidazole (1), their anionic and cationic forms, as well as the energetic, electronic, and structural characteristics of neutral, protonated, and deprotonated tautomers. According to the IR spectra, 1 exists in the crystalline state and in CCl4 and acetonitrile solution in the hydroxy form as two tautomers. A significant difference has been shown to exists in the EAS in acidic media of benzimidazoles, containing a benzene ring in the C2 position, as compared with the spectra of benzimidazoles with alkyl substituents in this position. Spectral characteristics are given which can be used to distinguish the mono- and dianionic forms of derivatives of 1.