Theoretical investigation of the interaction between monohalogenated ethenes and hydrogen peroxide

The complexes between monohalogenated ethenes CH2CHX (X = F, Cl, Br) and hydrogen peroxide (HP) have been studied theoretically at the MP2/6-311++G(3df,2p) level. The calculations include the optimization of the geometries, the vibrational frequencies and IR intensities of the ν(OH) and ν(CH) vibrations along with a natural bond orbital (NBO) analysis. The most stable complexes having binding energies between 7 and 12 kJ mol−1 have a cyclic structure characterized by OH…X and CH…O hydrogen bonds. Less stable complexes having binding energies of 6 kJ mol−1 are stabilized by two CH…O hydrogen bonds. The complexes are slightly more stable than the corresponding CH2CHX · H2O complexes, showing the predominance of the proton donor in determining the hydrogen bond energies. The variations of the NBO charges on the two partners are discussed. Blue shifts are predicted for the ν(CH) vibrations of the CH…O bonds and red shifts for the ν(OH) vibrations in the OH…X bonds. The data are discussed as a function of the change in hybridization of the C atom along with the occupation of the σ∗CH) orbitals. Intramolecular and intermolecular hyperconjugations are discussed as well. The geometric data and NBO parameters suggest that the strength of the CH…O hydrogen bonds are ordered according CH2CHF < CH2CHCl < CH2CHBr. An inverse order is found for the OH…X hydrogen bonds.