Non covalent interactions and internal dynamics in dimethoxymethane-water

The millimeter-wave absorption and Fourier transform microwave spectra of five isotopologues of the 1:1 adduct of dimethoxymethane-water have been measured in supersonic expansions. Each rotational transition appears as a quintuplet, due to the internal rotation of the two methyl groups, which are nonequivalent in the adduct. The water moiety, linked asymmetrically to dimethoxymethane, behaves as a proton donor to one of its oxygen atoms and interferes with the internal rotation of the farther methyl group through a C-H center dot center dot center dot O interaction. From the analysis of the observed splittings, the V-3 barriers to the internal rotation of the two methyl groups have been determined to be 6.83(8) and 6.19(8) kJ mol(-1). The hydrogen bond structural parameters have been determined, the O-H center dot center dot center dot O and C-H center dot center dot center dot O distances being 1.93(1) and 2.78(4) angstrom, respectively.