1758_ftp.pdf

JOURNAL OF RAMAN SPECTROSCOPY J. Raman Spectrosc. 2008; 39: 1–15 Published online 14 May 2007 in Wiley InterScience () DOI: 10.1002/jrs.1758 Vibrational spectra, X-ray and molecular structure of 1H - and 3H -imidazo[4,5-b]pyridine and their methyl derivatives: DFT quantum chemical calculations 1 ´ 1 1 1,2 czka,2 ∗ ´ 2 J. Lorenc, L. Dyminska, Z. Talik, J. Hanuza, M. M ¸ A. Waskowska and a L. Macalik2 1 Department of Bioorganic Chemistry, Institute of Chemistry and Food Technology, Faculty of Engineering and Economy, University of Economics, 53-345 Wrocław, Poland 2 Department of Solid State Spectroscopy, Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław, Poland Received 15 November 2006; Accepted 22 March 2007 Molecular structure, vibrational energy levels and potential energy distribution of 1H-imidazo[4,5- b]pyridine, 3H-imidazo[4,5-b]pyridine, 5-methyl-1H-imidazo[4,5-b]pyridine, 6-methyl-1H-imidazo[4,5- b]pyridine and 7-methyl-3H-imidazo[4,5-b]pyridine were determined using density functional theory (DFT) at the B3LYP/6-31G(d,p) level. The optimised bond lengths and bond angles are in good agreement with the X-ray data of 5-methyl-1H-imidazo[4,5-b]pyridine obtained in the present work (Pbca space group; + ˚ a = 8.660.2/, b = 11.078.2/, c = 11.078.3/ A, Z = 8). The N H group plays the role of a proton donor in a medium strong hydrogen bond of the type N–H· · ·N, linking the N-atom of the pyridi