Hydrogen bonding types

We will now consider an interesting case where sigma nonbonded interactions of the hydrogen bond type help to reinforce the conformational preference of sub-... 

Values of A[5( H) — 5( H)] for a large number of enols have been determined. The results are close to +0.6 ppm and point to double minimum potentials and strong hydrogen bonds. Low values are found for l,l,l,5,5,5-hexafluoropentane-2,4-dione (0.30 ppm) and 3-(4-methoxy-phenyl)pentane-2,4-dione (0.31 ppm), but these two species are of the same double minimum hydrogen-bond type and the O O bond length in 3-(4-methoxyphenyl)pentane-2,4-dione (i = 245pm Emsley et al., 1988a) is similar to that for other enols. 

In most cases, the chiral selector is simply added to the BGE. " Interactions between the analytes and the chiral selector will determine the stability of the diastereomeric complexes formed. The interactions involved in the chiral recognition process in CE are hydrophobic, electrostatic, Van der Waals and hydrogen bond-type interactions. Several reviews discuss the principles of electrophoretic chiral separations. 

Ito et al. (74) obtained a room-temperature spectrum of ethane adsorbed on an evaporated film of palladium. Absorptions were observed at 2850 and 2700 cm 1 characteristic of an alkyl species. The soft vCH 2700-cm 1 band implies the presence of agostic hydrogen-bond-type interactions of C-H bonds with surface metal atoms. 

The early development of enantioselective GC witnessed the use of packed columns containing CSPs and (in principle) apt for semipreparative-scale separations, i.e. in hydrogen-bonding-type CSPs (Gil-Av and Feibush, 1967), coordination-type CSPs (Golding et al., 1977) and inclusion-type CSPs (Koscielski et al., 1983). 

When utilized in the vision process, the Rhodonine chromophores are formed into a liquid crystalline state on the surface of a substrate, known generically as the protein opsin. It appears that the chromophores are held to the opsin substrate by very weak bonds of the hydrogen bond type. This linkage does not disturb the unique electronic configuration of the chromophoric material. 

Tamasi G, Botta F, Cini R (2006) DFT-molecular modeling analysis of C-H- -N and C-H- - -S hydrogen bond type interactions in selected platinum-purine/pyrimidine complexes. J Mol Struct... 

Hydrogen bond types that are widely used in organic crystal engineering, primarily D-H A where D, A = O or N, will inevitably be important in inorganic systems since the same functional groups that form such hydrogen bonds, i.e. carboxyl, amide, oxime, alcohol, amine, etc., can be present as part of organic... 

The rate of epoxidation is also affected by solvent. The reaction is particularly facilitated by chlorinated solvents. More polar solvents, particularly hydrogen bonding types, greatly decrease the rate of reaction. This considerable reduction... 

We believe that the Hycar 1312 is not cured. In these systems there exist only the van der Waals attractive and/or hydrogen bonding type forces between the epoxy matrix and the liquid rubber particles. In such two-phase systems the liquid rubber merely acts as a diluent and will show physical properties analogous to mechanical mixtures of two different polymers. 

Elgureo et ai, 1995). Among these hydrogen-bonded crystals, proton transfer is detected only in cyclic hydrogen-bonded types [25-27]. 

The wavenumber displacement of a solute vibration is a complex function of both solute and solvent properties and can be explained in terms of weak nonspecific electrostatic interactions (dipole-dipole, dipole-induced dipole, etc.) and of strong specific association of solute with solvent molecules, usually of the hydrogen-bond type [140], It should be realized that the duration of vibrational transitions is very short with respect to motion of the solvent molecules e.g. for an O—H stretching vibration, the frequency is ca. 10 s ). Thus, it is possible to observe such transitions even for short-lived entities such as may arise after a collision in the liquid phase (collision complexes) [140],... 

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