Hydrogen bonding contribution

Here the favorable geometrical arrangement with two hydrogen bonds contributes 14 kcal to the stability of the hydrogen bonded product, (7). These are called inter-molecular hydrogen bonds (inter means between). 

Quantitative estimation of hydrogen bond contribution to permeability and absorption processes of some chemicals and drugs. Eur. J. Med. Chem. 1998, 33, 799-807. 

Raevsky, O. A., Schaper, K.-J., Van de Waterbeemd, H., McFarland, J. Hydrogen bond contribution to properties and activities of chemicals and drugs. In Molecular Modeling and Prediction of Bioactivity, Gundertofte, K., Jorgensen,... 

Computational mutation of Tyrl 13 to Phe resulted in a 700-fold decrease in the binding affinity of AMP relative to wild-type FBPase. The calculated results were consistent with earlier experimental data.28 Since Tyrl 13 hydrogen bonds to both the 5 oxygen and the 3 hydroxyl, it is unclear how much each hydrogen bond contributes to AMP binding affinity. 

Like the Ccirboxylic acids, the primeiry and secondary cimides have a hydrogen bonding contribution to their intermolecular forces. 

The figures in brackets are the increments resulting from the introduction of hydroxyl or carboxyl groups, For these simply related structures it would seem that the sublimation heats are derived addi-lively. Whilst this is not generally so, there are probably many other sets of structures for which this approximation applies. Without going into further examples here, it is obvious that much can be learnt of hydrogen bond contributions from lattice energies. 

Table I Hydrogen bond contributions (kJ mol 1) to the total lattice energy of four dihydrogenphosphate salts, [AH][H2P04] a...

The other components can also be estimated using additive functional group contributions, and tables of group contributions for polarand hydrogen-bonding contributions are available (Hansen and Beerbower, 1971 Van Krevelen and Hoftyzer, 1976 Barton, 1983). If we label the polar functional group contributiorFp, the polar contributions are summed in this fashion ... 

We have now collected almost all the pieces required for a first version of COSMO-RS, which starts from the QM/COSMO calculations for the components and ends with thermodynamic properties in the fluid phase. Although some refinements and generalizations to the theory will be added later, it is worthwhile to consider such a basic version of COSMO-RS because it is simpler to describe and to understand than the more elaborate complete version covered in chapter 7. In this model we make an assumption that all relevant interactions of the perfectly screened COSMO molecules can be expressed as local contact energies, and quantified by the local COSMO polarization charge densities a and a of the contacting surfaces. These have electrostatic misfit and hydrogen bond contributions as described in Eqs. (4.31) and (4.32) by a function for the surface-interaction energy density... 

These forces are not appreciably influenced by one another, and so may be assumed to be additive. The surface tension of water may, therefore, be considered as the sum of a dispersion force contribution, and a hydrogen bonding contribution, yw - i.e. 

The study of some methyl derivatives of formamide would be very helpful in determining the hydrogen bonding contribution unfortunately, the lines are very weak and the spectra are incompletely observed 6°). 

Ifwe look at the pKan values in the gas phase, we can eliminate the hydrogen bonding contribution and we find the basicity increases in the order we expect, that is, tertiary > secondary > primary. 

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