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.

The MP2/6-311++G(2d,2p) study of complexes between dimethyl ether (DME) and H2O, hydrogen halides, dihalogens, halomethanes, DME, Li+, and H+ demonstrates that the C-H bonds of DME are not involved in H-bonding. However, their stretches are blue-shifted. We show that these blue shifts originate from the negative intramolecular C-O - C-H coupling.