Hydrogen bonding strengths

The most accurate calculated values of the binding energies of a series of homodimers are presented in Table 1. Note that most of these values have still not been completely pinned down to the nearest 0.1 kcal/mol, but retain a range of uncertainty, depending upon the specific level of theory. Nonetheless, the trends are rather clear. 

The abilities of the various molecules to act in the capacity of either a proton donor or acceptor are illustrated by the assortment of mixed dimers listed in Table 2. Although the electronic contributions to the binding energies were not computed at the highest level of theory currently available, we are most concerned here with a fair comparison. All values were computed at the same level, SCF, using the 6-31G basis set. 

Strengths of hydrogen bondsa in mixed dimers (kcal/mol) 

The opposite order, wherein the more basic molecule serves as the most efficient proton acceptor, is also obvious from examination of the columns of the table. 

Another important observation relates to the fact that the rate of change in each row is greater than that in a given column. In other words, the strength of the H-bond is more sensitive to the nature of the donor than to the acceptor. 

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Thermochemistry. Thermodynamic considerations ate of utmost importance in fluorinations. Table 1 is based on JANAF data (25) for CH, which indicate an average carbon-hydrogen bond strength of 410.0 kj/mol (98 kcal/mol) based on the atomization energy of CH. ... 

It will be noted that as the hydrogen bond strength increases, Py (H2O) > Py(CH2Cl2) > Py(CHCl3), the relative intensity ratio of the two ring modes increases and they may be used to assess the strength of the hydro-... 

For reviews of the relationship between hydrogen bond strength and acid-base properties, see Pogorelyi, V.K. Vishnyakova, T.B. Russ. Chem. Rev, 1984, 53, 1154 Epshtein, L.M. Russ. Chem. Rev, 1979, 48, 854. 

Because of the exposed histidine ligands of the [2Fe-2S] cluster, the Rieske is capable of binding quinones in a redox-dependent manner. The variation of the hydrogen bond strength and of the electrostatic properties will control the movement of the catalytic domain of the Rieske protein. Therefore, the function depends on the unique structural and electrochemical properties of the Rieske cluster. 

Infrared Hydroxyl Absorption Bands and Hydrogen-bonding Strength (Xv cm ) for Various Sugars and Their Relative Sweetness ... 

Raevsky, 0. A. Hydrogen bond strength estimation by means of HYBOT. In Computer-Assisted Lead Finding and Optimization, Van de Waterbeemd, H., Testa, B., Folkers, G. (eds.), Wiley-VGH, Weinheim, 1997, pp. 357-378. 

Kumar, G. A., McAllister, M. A., 1998, Theoretical Investigation of the Relationship Between Proton NMR Chemical Shift and Hydrogen Bond Strength , J. Org. Chem., 63, 6968. 

Cser A, Nagy K, Biczok L (2002) Fluorescence lifetime of Nile red as a probe for the hydrogen bonding strength with its microenvironment. Chem Phys Lett 360(5-6) 473-478... 

Raevsky, O., Hydrogen bond strength estimation by means of the HYBOT program package, in Computer-assisted lead finding and optimization, H. van de Waterbeemd, B. Testa and G. Folkers, eds, Verlag Helvetica Chimica Acta, Basel, 1997, 367-378. 

MolSurf parameters [33] are descriptors derived from quantum mechanical calculations. These descriptors are computed at a surface of constant electron density, with which a very fine description of the properties of a molecule at the Van der Waals surface can be obtained. They describe various electrostatic properties such as hydrogen-bonding strengths and polarizability, as well as Lewis base and acid strengths. MolSurf parameters are computed using the following protocol. 

Hydrogen bonding is a special type of acid-base interaction (see Chapter 9). Probably the most important equation relating hydrogen bond strengths is the equation known as the Drago four-parameter equation,... 

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