Hydrogen bonding vibrational modes

The other group of bands at 100-200 cm should be assigned to osdl-lations of the H-bond. It is known that H-bonds can form planar cyclic MAA dimers and three of the six hydrogen bond vibrational modes of such dimers (torsional, asymmetric deformation and asymmetric stretching) must be active in IR absorption. From the calculations and the experiment [150], the stretching mode of H-bond may be assigned to the band observed at 136 cm" and the deformation and torsional modes to the bands at 97 cm" and about 50 cm" respectively (the latter is not shown in Fig. 32). The weak band observed at 113 cm" is also tentatively assigned to the torsional mode. 

Notice that the IR pattern inherent for isolated phenol and water molecules (equation 40) is nearlyretamedinthePhOH-wi-2structure. The H-bond vibrational mode Vff = 125.5 cm is lower than in PhOH-Wi-1, implying that the hydrogen bonding in the PhOH-Wi-1 structure is stronger. 

Vibrational assignments have been proposed from the IR and Raman spectra of (Me3SiO)3PHI - Table 11. Note that vPH is at 2172 cm in (Me3SiO)2PH." " Values of vPH at low temperatures for ( BuO)2P(0)H and CBuO)2P(0)H were used to probe hydrogen bonding." " " Vibrational parameters obtained for PH2D include V2 (inversion mode) 891.9134565(472) cm V4b (HPD bend) 969.4805730(610) cm-i and V4a (HPH bend) 1093.5708756(433)... 

Heisler, I. A. Meech, S. R. (2010). Low-frequency modes of aqueous alkali halides solutions glimpsing the hydrogen bonding vibration. Science, 327, 857-860 Holbrey, J. D. Seddon, K R. (1999). The phase behaviour of l-alkyl-3-methylimidazolium tetrafluoroborates ionic liquids and ionic liquid crystals. Journal of Chemical Society, Dalton Transaction, 2133-2139... 

In addition to sp C—H stretching modes there are other stretching vibrations that appear at frequencies above 3000 cm The most important of these is the O—H stretch of alcohols Figure 13 34 shows the IR spectrum of 2 hexanol It contains a broad peak at 3300 cm ascribable to O—H stretching of hydrogen bonded alcohol groups In... 

In addition, the frequency cooo, as well as the tunneUng distance can also be extracted from the same empirical data. Thus all the information needed to construct a PES is available. Of course, this PES is a rather crude approximation, since all the skeleton vibrations are replaced by a single mode with effective frequency cooo and coupling parameter C. From the experimental data it is known that the strong hydrogen bond (roo < 2.6 A) is usually typical of intramolecular hydrogen transfer. 

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