On blue shifts of C–H stretching modes of dimethyl ether in hydrogen- and halogen-bonded complexes

A systematic investigation of a representative series of intermolecular complexes formed between dimethyl ether (DME) and various interacting partners such as H2O, hydrogen halides, dihalogens, halomethanes, DME, and the ions Li+ and H+ was performed at the MP2/6-311++G(2d,2p) computational level. Although, except (DME)2, DME–HCF3, DME–HCClF2, and DME–HCCl2F, the C–H bonds of DME are not involved in the hydrogen bonding of these complexes, their C–H stretching frequencies are all blue-shifted. It is shown that the mechanism of these blue shifts originates from the existence of a negative intramolecular coupling between the C–O and C–H bonds inherent to the DME molecule.