Linear correlation between change of stretching frequencies and change of the N-H and C-H bond lengths in all complexes has been reported in equation (1) and (2). Besides, the change of the N-H bond lengths and their stretching frequencies as a function of the change of occupation of σ*(N-H) orbitals and that of s-character of N hybrid orbitals were obtained as in expression (3) and (4). | Journal of Chemistry, Vol. 47 (5), P. 535 - 541, 2009 THE BLUE SHIFTS OF THE C-H AND N-H BONDS IN THE COMPLEXES OF CHX3 (X = F, Cl, Br) AND HNO: A THEORETICAL STUDY Received 13 Sep 2007 Nguyen Tien Trung1,2*, Tran Thanh Hue2 1 Faculty of Chemistry, Quy Nhon University 2 Faculty of Chemistry, Hanoi National University of Education abstract All calculations were performed at the high level of theory (MP2/6-311++G(d,p)). Five separate minima were identified on the potential energy surface of each complex pairing CH3X with HNO. In general, strength of complexes increases in going from F to Cl to Br, which is consistent with respective decrease of deprotonation enthalpy of the C-H bond respectively. All the C-H and N-H bonds are shortened upon complexation, corresponding to increase in their stretching frequencies. It is interesting that blue shift is observed in the N-H bonds; such a contraction in the N-H covalent bond is extremely rare. Linear correlation between change of stretching frequencies and change of the N-H and C-H bond lengths in all complexes has been reported in equation (1) and (2). Besides, the change of the N-H bond lengths and their stretching frequencies as a function of the change of occupation of σ*(N-H) orbitals and that of s-character of N hybrid orbitals were obtained as in expression (3) and (4). I - Introduction The hydrogen bond plays an important role in many chemical, physical and biochemical processes [1, 2]. Recently, a new type of intermolecular bond, commonly designated as a blue-shifting hydrogen bond, continues to receive a good deal of both experimental and theoretical attention. The majority of these blue-shifting hydrogen bonds contains a C-H bond as the proton donor. In general, the N-H bond will shift to the red of stretching frequency because of its more polarization. However, there are some very small numbers of exceptions recently reported for the N-H bond that the blue shift is found in the type of the .
