| 19256510 |
Trung NT, Hue TT, Nguyen MT: Remarkable blue shifts of C-H and N-H stretching frequencies in the interaction of monosubstituted formaldehyde and thioformaldehyde with nitrosyl hydride. J Phys Chem A. 2009 Apr 2;113(13):3245-53.
Weak interactions of monosubstituted formaldehydes and thioformaldehydes with nitrosyl hydride were investigated by using ab initio MO calculations at the MP2/aug-cc-pVTZ level. Thirty two equilibrium structures having different complex forms were located on the corresponding potential energy surfaces (all having C (s) symmetry). Obtained binding energies, which include both ZPE and BSSE corrections, range from 7 to 14 kJ x mol (-1) and 6 to 12 kJ x mol (-1) for complexes of substituted formaldehydes and thioformaldehydes, respectively. In each geometrical structure, the (XCHO,HNO) complex is consistently more stable than the (XCHS,HNO) complex. The H-bond strength significantly increases when one H atom is replaced by a methyl group in both formaldehyde and thioformaldehyde. When replacing H by a halogen atom, the binding energy tends to decrease. It is remarkable that all the C-H and N-H bonds are shortened upon complexation, resulting in an increase of their stretching frequencies. Furthermore, the blue shifts are consistently observed for the interacting N-H bonds in N-H...X, Z, with X = F, Cl, Br, and Z = O, S; such contraction of a covalent N-H bond is extremely rare. In addition, the N-H bond length contraction and its frequency blue shift in the N-H...S complex have been revealed for the first time. |
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