Structural and spectroscopic evidence of hydrogen bonding in 3-bromo-5-hydroxy-2,6-dimethylpyridine and 3-chloro-5-hydroxy-2,6-dimethylpyridine
作者:J. Hanuza、M. Ma̧czka、A. Waśkowska、W. Oganowski、M. Andruszkiewicz、H. Ban-Oganowska、B. Lutz、J.H. van der Maas
DOI:10.1016/s0022-2860(96)09359-3
日期:1997.2
The crystal structures of 3-chloro-5-hydroxy-2,6-dimethylpyridine (ClHDMP) and 3-bromo-5-hydroxy-2, 6-dimethylpyridine (BrHDMP) were determined at room temperature. Although ClHDMP is monoclinic, space group P2(1)/c, and BrHDMP is orthorhombic, space group Pna2(1), the molecular conformation is essentially the same in both compounds. The structure consists of two parallel infinite chains of formula units linked through hydrogen bonds of the type O-H...N. There is no interconnection between the chains.Fourier transform IR and Raman spectra of ClHDMP and BrHDMP were measured in the 50-3500 cm(-1) frequency range at room temperature. The vibrational assignment of the observed bands is proposed. The appearance of the characteristic vibrational features in the spectra of these compounds is discussed in terms of strong asymmetric hydrogen bonding. The bands observed at approximately 2800-2850, 2500-2550 and 1800-1850 cm(-1) are assigned to the O-H stretching modes and those at 1400-1410 and 900-950 cm(-1) to delta(O-H) and gamma(O-H) modes, respectively. The nu(O-H) vibrations of the hydrogen bonds appear at 130-140 cm(-1). The calculation of gamma(O-H) frequencies and other parameters describing the strong hydrogen bonding, such as the Fermi coupling constant \W\, the separation of the unperturbed vibrational levels (Delta(0)), etc., has been performed. The positions of gamma(O-H) bands have been found to agree with those predicted from the perturbed nu(O-H) patterns. Comparison of the structural and vibrational characteristics of hydrogen bonds in ClHDMP and BrHDMP has indicated that a stronger hydrogen bonding exists in the bromo-derivative. (C) 1997 Elsevier Science B.V.