Theoretical study of the blue-shifting hydrogen bonds between CH2X2 and CHX3 (X=F, Cl, Br) and hydrogen peroxide

This work deals with a theoretical study of the interaction between CH2X2 and CHX3 (X=F, Cl, Br) and hydrogen peroxide (HP). The optimized geometries, binding energies and harmonic vibrational frequencies are calculated at the MP2/6-311++G(3df, 2p)//MP2/6-31G(d,p) level. The results of a natural bond orbital analysis (NBO) are reported as well. All the complexes are characterized by a cyclic structure, the complexes being stabilized by CH⋯O and OH⋯X interactions. Complex formation results in a contraction of the CH bond and an elongation of the OH bond. The binding energies range between 11.7 and 13.8 kJ mol−1. The ν(CH) stretching vibrations show the characteristic features of the blue-shifted hydrogen bonds. In contrast, the ν(OH) vibrations are red-shifted. The NBO analysis shows that the charge transfer taking place from the CH2X2 or CHX3 molecules to HP is small and that complex formation induces an electronic reorganization mainly in the XCH part of the molecule involved in the interaction. In most of the complexes, there is a very small increase of the occupation of the σ*(CH) orbital and an increase in s-character of the C hybrid orbital in the CH⋯O bond. A quantitative correlation between the contraction of the CH bond and the variation of these two parameters is presented. In contrast, the lengthening of the OH bond mainly depends on the occupation of the σ*(OH) orbital. The results are compared with theoretical data on other blue-shifted hydrogen bonds.