Polarization enhanced hydrogen bonds

Chains of cooperative hydrogen bonds are commonly seen in crystal structures of mono- and oligosaccharides. Shown below is a picture of the crystal structure of /)-nitrophenyl a-maltohexaoside. A long running chain of hydrogen bonds can be identified along the 2,3-vicinal 

Hindricks, W., and Saenger, W. Crystal and Molecular Structure of the Hexasaccharide Complex (p-Nitrophenyl a-Maltohexaoside)Bal3-27H20. /. Am. Chem. Soc., 112,2789-2796 (1990). 

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An ab initio MO calculation by Jorgensen revealed enhanced hydrogen bonding of a water molecule to the transition states for the Diels-Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile, which indicates that the observed rate accelerations for Diels-Alder reactions in aqueous solution arise from the hydrogenbonding effect in addition to a relatively constant hydrophobic term.7,76 Ab initio calculation using a self-consistent reaction field continuum model shows that electronic and nuclear polarization effects in solution are crucial to explain the stereoselectivity of nonsymmetrical... 

The original Hildebrand and Scott equation was obtained on the premise that nonpolar liquids possessed a spherical symmetry. For liquids without symmetry, the molecules tend to orient. The result of orientation could contribute to the departure of the surface properties from the bulk properties of polar and hydrogen-bonded liquids. This departure should be enhanced in the case of a long-chain polymer. 

The spectrum of adsorption mechanisms is wide and depends on the specific properties of a given adsorption system. It comprises induced dipolar or polarization effects, hydrogen bond formation, acid-base affinity, and other interactions lying somewhere between the strictly nonpolar dispersion and ion-ion coulombic forces. They can alter the extent and mode of the process. For example, if the adsorbate contains an electron-rich group and the solid support has strongly polarizing sites, attraction between them markedly enhances the energetics of adsorption [77]. 

Extracted pitch behavior is also dependent on the pltch/solvent ratio used for the separation. Altering ratios will affect both the weight percent dissolved, and the properties of an extract. Increasing the pltch/solvent ratio of a polar or hydrogen bonded solvent can decrease their effectiveness and shift and reduce the size of the enhanced solubility region on solubility plots. In this way an over-effective solvent can be moderated so it extracts a mesophase forming sample. 

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