Hydrogen bond donation surfaces

The PSA represents a very useful property for predicting absorption. It is usually defined as those parts of the van der Waals or solvent-accessible surface of a molecule that are associated with hydrogen bond-accepting capability (e.g., N or O atoms) and hydrogen bond-donating capability (e.g., NH or OH groups). Three types of PSA have been used in studying absorption ... 

Our focus in this chapter shall be primarily upon the surface electrostatic potential, specifically its most positive and most negative values, denoted by Vs, max and Vs,min, respectively. There may be several local and absolute maxima and minima on a given surface. They indicate the most positive and negative sites. The former are often associated with hydrogens, especially acidic ones, and the latter with lone pairs, tt electrons of unsaturated molecules and strained bonds. We have demonstrated that Vs niax and Vs nim correlate well with measures of hydrogen bond donating and accepting tendencies . 

Murray, J. S. and Politzer, P., Correlation betwen the solvent hydrogen-bond-donating parameter a and the calculated molecular surface electrostatic potential, J. Org. Chem. 56,6715-6717 (1991). 

Murray, J.S. and Politzer, P. (1991). Correlations Between the Solvent Hydrogen-Bond-Donating Parameter a and the Calculated Molecular Surface Electrostatic Potential. J.Org.Chem., 56, 6715-6717. 

It has been our experience that 7s(r) and Vs(r) play different but complementary roles with respect to molecular reactivity [71,83-85], Vs(r) is effective for treating noncova-lent interactions, which are primarily electrostatic in nature [74,86-89], For instance, a variety of condensed-phase physical properties - boiling points, critical constants, heats of phase transitions, solubilities and solvation energies, partition coefficients, surface tensions, viscosities, diffusion constants and densities - can be expressed quantitatively in terms of one or more key features of Vs(r), such as its maximum and minimum, average deviation, positive and negative variances, etc. [80,90-92], Hydrogen bond donating... 

Depending upon the chemical structure of the solute, the addition of hydrogen bond donating (methanol) or hydrogen bond accepting (ethyl ether) solvents to the mobile phase may improve selectivity (i.e., enhance resolution) due to unique interactions with the solute and/or modification of the silica surface [51,52]. Therefore, e° cannot predict any enhancement in selectivity that one solvent pair may provide over another since this is often a result of specific mobile phase/solute functional group interactions. 

This involves deposition of the catalyst on the accessible surface of the support. The complex is held on the surface by rather weak interactions, such as van der Waals forces, hydrogen bonding, or a donating bond. The stability of the complex on the surface is determined by its solubility in the reaction solvent and/or the complexation of reagents and products. 

The water molecules form polymeric chains which include homodromic and antidromic six-membered hydrogen-bonded circles each one of the water species is either threefold or fourfold coordinated, donating at least one H-bond to the surface of a neighboring bilayer. 

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