Hydrogen bonding ability

Knowledge of the spatial dimensions of a molecule is insufficient to imderstand the details of complex molecular interactions. In fact, molecular properties such as electrostatic potential, hydrophilic/lipophilic properties, and hydrogen bonding ability should be taken into account. These properties can be classified as scalar isosurfaces), vector field, and volumetric properties. 

BW Beck, IB Koerner, RB Yelle, T Ichiye. Unusual hydrogen bonding ability of sulfurs m Fe-S redox sites Ah initio quantum and classical mechanical studies. I Phys Chem B, submitted. 

Closely related to the basicity of pyridine is its hydrogen-bonding ability two indices of this property have been measured for a very short series of substituted pyridines and are very well correlated by CT-values. ... 

Shindo studied the hydrogen-bonding ability of a fairly long series of substituted pyridine 1-oxides with methanol in chloroform solution and found that the OH frequency of the hydrogen-bonded OH group in methanol is well correlated with the <7-values. For four compounds, the intensity of the same band is also well correlated. In a similar study the OH frequencies of phenol vary monotonically with the CT-values, but not in a linear fashion. 

Alternating values of E and of In A were found for n = 0 to 4 and increasing values above n = 5. This observation was correlated with the hydrogen-bonding ability of these acids E+ is proportional to the concentration of associated carboxy groups19. Their experimental observations are, to some extent, in agreement with the results from Mat-suzaki and Mitani268. ... 

Other considerations aside, the use of dilute reagents minimizes effects of nonideality. This allows the use of concentrations in place of activities. Of course, the time scale, the sensitivity of the analytical method at different concentrations, and the use of other reaction components introduce additional considerations. Tied closely to this decision is the choice of solvent. Reaction rates may (or may not) be affected by such variables as polarity, dielectric constant, hydrogen-bonding ability, donor capacity, and viscosity. A change in solvent may change not only the rate but also the mechanism and possibly even the products. One cannot even assume that the net reaction is the... 

Water was also investigated as a proton donor for the hydrogen bond with DMSO and other Lewis bases at infinite dilution detected by means of 1H NMR54-69. A comparison of the hydrogen bonding ability of DMSO in various other aprotic solvents was presented by Delpuech70 who measured the H-NMR chemical shift of CHC13. 

A comparison of these p/CHB values at constant pK of the bases reveals that the most important factor which determines the correlation between the structure and the hydrogen bonding ability depends on the electronegativity of the acceptor atom in the Lewis bases employed. Thus, the strength of the basicities of the oxygen compounds described above is... 

They have also demonstrated that a linear energy relationship exists between pKa values of sulphoxides and the hydrogen bonding ability which was determined by IR-stretching shift of the OH band in PhOH in CC14. Oae and coworkers173 determined the pKa values of diaryl sulphoxides and found that the substituent effect does not correlate with the Hammett o values but approximately with the a values. The pKa values thus obtained are summarized in Table 19. 

As we have implied, the ability of these host molecules to bind guests is often very specific, often linked to the hydrogen-bonding ability of the host," enabling... 

The hydrogen-bonding ability of triethylphosphine with pyrrole, [see... 

Thioureas are most commonly prepared from reaction of isothiocyanates with amines. Also there are some reports on reactions of anime or carbodiimides with several thionating reagents. AA -Disubstituted thioureas bearing double NH groups have been developed as sensors, and as catalysts because of their hydrogen bonding ability. A,A -Disubstituted thiourea-linked sugar chains have been prepared by the reaction of isothiocyanate with amine. 

Chiral fe-thiourea-type catalysts effectively provide the Baylis Hillman reaction with cyclohexenone and aldehydes.181 In several reactions, thiourea derivatives have been used as significant and specific catalyst because of their intermolecular hydrogen bonding ability (Scheme 74).182 186... 

The same effect is typical of the reactions of alkoxyl radicals with phenols, that is, these reactions are much slower in solvents capable of forming hydrogen bonds with O—H and N—H groups [50]. MacFaul et al. [50] proposed a universal scale for correlating the reactivities of phenols and the hydrogen-bonding abilities of solvents. 

FIGURE 27.6 (See color insert following page 302.) rj(r) can be used for the estimation of the electrostatic interaction and the hydrogen bonding ability. (Reprinted from Mignon, P., Loverix, S., Steyaert, J., and Geerlings, P., Nucl. Acids Res., 33, 1779, 2005. With permission.)... 

In contrast, the Py scale, based on the relative intensities of vibronic bands of pyrene, appears to be relatively insensitive to hydrogen bonding ability of solvents. 

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