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-HCCIF2, 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. (c) 2006 Elsevier B.V. All rights reserved.