Theoretical studies on tautomerism and IR spectra of C-5 substituted imidazoles

Total energy. Gibbs free energy, the highest pi and sigma electronic states , and IR spectra were calculated for twelve C-5 substituted imidazoles at t he MP2/6-311++G** level. The COOH and BH? groups stabilize strongly the N-1 -H tautomer, the F and OH groups stabilize strongly the N-3-H tautomer, whe reas the NH2 and NO2 groups favours the N-3-H tautomer with a similar, medi um strength. The calculated IR spectra of the imidazoles studied reveal dif ferences between the two tautomers, but they do not follow the order of der ivatives emerging from the energetics. (C) 2001 Published by Elsevier Scien ce B.V.