Quantum Chemical Studies on Prototautomerism of 1H-Imidazo[4,5-C]pyridine

The structural features of the 1H-imidazo[4,5-c]pyridine (ICPY) tautomers and homodimers of the most stable tautomers have been studied by quantum chemical methods. FTIR and Raman spectra of the ICPY were recorded in the range of 4000-60 cm(-1) and 3500-5 cm(-1). The predominant tautomer among four possible isomers of ICPY were determined. The optimized geometries and vibrational frequencies of possible ICPY tautomers and dimers were computed by B3LYP/DFT method with 6-311++G(d,p) and 6-31G(d) basis sets. All vibrational frequencies assigned in detail with the help of total energy distribution (TED) and isotopic shifts. ICPY dimeric forms were also characterized according to their hydrogen bonding interactions, and it has been found that the most stable ICPY homodimer establishes moderate strong N-H center dot center dot center dot N type hydrogen bond. H-1 NMR, C-13 NMR, and N-15 NMR properties have been calculated for all tautomeric forms using the gauge independent atomic orbital (GIAO) method. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 2944-2959, 2011