Basicity of azoles: VII. Protonation and conformations of 2-(2-pyridyl)benzimidazoles by UV spectral data

Absorption bands in the UV spectra of 2-aryl(hetaryl)benzimidazoles were assigned on the basis of AM1(CI) semiempirical calculations. The energy gap between the S-1 and S-2 states of these compounds depends on the molecular conformation. Equilibrium torsion angles in substituted 2-phenylbenzimidazol...

Full description

Saved in:
Bibliographic Details
Published inRussian journal of general chemistry Vol. 70; no. 4; pp. 583 - 595
Main Authors Turchaninov, VK, Vokin, AI, Baikalova, LV, Shulunova, AM
Format Journal Article
LanguageEnglish
Published NEW YORK MAIK NAUKA/INTERPERIODICA 01.04.2000
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
Online AccessGet more information

Cover

More Information
Summary:Absorption bands in the UV spectra of 2-aryl(hetaryl)benzimidazoles were assigned on the basis of AM1(CI) semiempirical calculations. The energy gap between the S-1 and S-2 states of these compounds depends on the molecular conformation. Equilibrium torsion angles in substituted 2-phenylbenzimidazoles in solution were estimated. Analysis of the UV spectra recorded at a low HCl concentration and the results of AM1(CI) calculations of the electronic spectra indicate that 2-(2-pyridyl)benzimidazoles are protonated at the N-3 atom of the imidazole fragment and that the protonation induces shift of conformational equilibrium. Raising the concentration of proton donor leads to formation of dications which have a nonplanar struture. The most basic center of 2-(2-pyridyl)benzimidazoles in the gas phase is also the imidazole N-3 atom. According to the AM1 calculations, protonation of the pyridine fragment is less favorable because of a larger energy required for bond reorganization.
ISSN:1070-3632