Weak, Improper, C−O···H−C Hydrogen Bonds in the Dimethyl Ether Dimer

Abstract

The ground-state rotational spectrum of the dimethyl ether dimer, (DME)(2), has been studied by molecular beam Fourier transform microwave and free jet millimeter wave absorption spectroscopies. The molecular beam Fourier transform microwave spectra of the (DME-d(6))(2), (DME-(13)C)(2), (DME-d(6))...(DME), (DME-(13)C)...(DME), and (DME)...(DME-(13)C) isotopomers have also been assigned. The rotational parameters have been interpreted in terms of a C(s) geometry with the two monomers bound by three weak C-H...O hydrogen bonds, each with an average interaction energy of about 1.9 kJ/mol. The experimental data combined with high-level ab initio calculations show this kind of interaction to be improper, blue-shifted hydrogen bonding, with an average shortening of the C-H bonds involved in the hydrogen bonding of 0.0014 A. The length of the C-H...O hydrogen bonds, r(O...H), is in the range 2.52-2.59 A.

Molecular Beam Rotational Spectrum of Cyclobutanone–Trifluoromethane: Nature of Weak CH⋅⋅⋅OC and CH⋅⋅⋅F Hydrogen Bonds

“…The O···H and F···H distances are in line with those observed for the complexes oxirane-TFM, [6] oxirane-difluoromethane [7] and dimethyl ether dimers, [5] once the different nature of C=O···H and C-O···H hydrogen bonds is taken into account. Actually, the F···H distance is slightly longer than that of other complexes (about 0.1 ).…”

“…[4,[6][7][8] The deviation from linearity of the C-H···O and C-H···F angles is considerable (51 and 668, respectively), as seen in previous cases. [5][6][7] This reveals the weak hydrogen bond nature of both types of competing interactions. The C-H···O bond is bent by presence of the C-H···F interactions and vice versa.…”

“…Rotational spectroscopy combined with supersonic expansions has been recently applied in order to study structural and energetic features of these weak interactions. C-H···F and C-H···O linkages were revealed to be the main factors in the formation of isolated cages such as difluoromethane [4] and dimethyl ether [5] dimers. The relative strength of these two interactions has been recently estimated through the study of the rotational spectrum of the oxirane-trifluoromethane, [6] oxirane-difluoromethane, [7] 1,1-difluoroethene-dimethyl ether [8] and trifluoroethene-dimethyl ether [8] adducts.…”

Dynamical Behavior and Dipole–Dipole Interactions of Tetrafluoromethane–Water

“…It has been shown that the OÀH···Cl hydrogen bond is slightly preferred to the O À H···F one, [8] but their energies have been estimated to be rather small (4-5 kJ mol À1 ). [8] These energy values are similar to those estimated for weak C À H···O, [9] C À H···F [10] or CÀH···p [11] interactions, which are classified as weak [12] or blue-shifted hydrogen bonds. [1] The simplest molecules containing halogen atoms (F 2 and ClF) react with water.…”

Glory‐Scattering Measurement of Water–Noble‐Gas Interactions: The Birth of the Hydrogen Bond

“…The relevance of the effect can be discussed quantitatively: Taking Kr as the study case for comparison of theory and experiment, we see that the binding energy (Figure 3) is about 1 kJ mol À1 higher than e = 1.65 kJ mol À1 , which can be compared with the expected value of 1.37 kJ mol À1 for pure vdW interactions (Table 1). The magnitude of the binding energy for Kr and Xe is therefore in the range of the so-called weak hydrogen bonds [21,22] (strong hydrogen bonds can be up to an order of magnitude stronger), and it is important to stress that only a fraction (ca. 50 % for Kr) is accounted for by vdW forces.…”