Hydrogen bonding frequency shifts related

Just as in our abbreviated descriptions of the lattice and cell models, we shall not be concerned with details of the approximations required to evaluate the partition function for the cluster model, nor with ways in which the model might be improved. It is sufficient to remark that with the use of two adjustable parameters (related to the frequency of librational motion of a cluster and to the shifts of the free cluster vibrational frequencies induced by the environment) Scheraga and co-workers can fit the thermodynamic functions of the liquid rather well (see Figs. 21-24). Note that the free energy is fit best, and the heat capacity worst (recall the similar difficulty in the WR results). Of more interest to us, the cluster model predicts there are very few monomeric molecules at any temperature in the normal liquid range, that the mole fraction of hydrogen bonds decreases only slowly with temperature, from 0.47 at 273 K to 0.43 at 373 K, and that the low... 

A clear correlation between isotropic H chemical shift and the frequency of the O-H stretching vibration has been reported [61] for surface hydroxyl groups in zeolites and related materials, as well as for water molecules in solid hydrates and strongly hydrogen bonded protons in inorganic solids. 

Gould, I. R., and Hillier, I. H., The relation between hydrogen-bond strengths and vibrational frequency. shifts A theoretical. study of complexes of oxygen and nitrogen proton acceptors and water, J. Mol. Struct. (Theochem) 314, 1-8 (1994). 

Badger (100) There appears to be a relation between the energy of a hydrogen bond and the shift in frequency of the O—H bands. Badger noted that carboxylic acids did not seem to fit the postulated relation, and in the same year Herman expressed doubt that there exists a simple relation between Avs/vs and AH (908). Fox and Martin used the Morse curve to show that Avg/va should be related to AH (684), but Davies found agreement with experimental data only within a factor of two (489). Nevertheless, there has been a general acceptance of the proposal that Ava/va provides an index of AH of H bond formation. 

Chemical shifts (S 13C NMR shifts related to Cl) of a large number of 3- or 4-substituted anilines are correlated with infrared N—H frequency data and with Hammett sigma values. An intermolecular hydrogen bond, as depicted in 62 and 63 (Scheme 10), was indicated to be present, on the basis of the plots of <>13C1 versus Vasym of NH2 group frequencies in chloroform100. 

The enthalpy of hydrogen bond in cyclic dimers (Fig. 20a) in the ABA and AOBA is equal to —35.3 0.8 kJ/mol per hydrogen bond at T 300 K. For the quantitative estimation of the enthalpy the Iogansen method [296] has been applied, which is based on the analysis of the shift of the frequency of twisting vibration pOH and that of the gravity center of the Voh band of associates with relation to the corresponding shifts for monomers. The determination of frequencies pQ on and of ABA and AOBA monomers, which are needed... 

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