Theoretical investigation of the conformation, acidity, basicity and hydrogen bonding ability of halogenated ethers

Abstract

MP2/6-311++G(d,p) calculations have been carried out to investigate the conformation, protonation and the hydrogen bonding interactions with water of several halogenated ethers (CH₃OCH₂Cl, CH₂ClOCH₂Cl, CH₃OCHCl₂, CHFClOCHF₂). The optimized geometries, ν(CH) harmonic vibrational frequencies and the SAPT decomposition of the interaction energies are studied. The interaction with one water molecule gives several stable structures characterized by O_wH_w⋯O and CH⋯O_w hydrogen bonds or by O⋯Cl halogen bonding. The MP2/CBS calculated binding energies of different complexes between the halogenated ethers and water vary between 1.7 and 7.7 kcal mol⁻¹. The energies of these structures are discussed as a function of the proton affinity of the ethers and the deprotonation enthalpy of the CH bonds. The contraction of the CH bonds and blue shifts of the corresponding stretching vibrations in the O-protonated ethers and their O⋯H_wO_w complexes are compared. A natural bond orbital analysis has revealed that substitution of the H atoms by one or several halogen atoms has a great influence on the hyperconjugative effects from the two non-equivalent O lone pairs to relevant antibonding orbitals, and the subsequent geometry of the hydrogen bonded complexes.