Isolated hydrogen bonds

The connection between energies and geometry must be empirical or indirect through theoretical hypotheses and calculations. This connection is further complicated by the other intermolecular interactions in crystals. The hydrogen-bond lengths observed in crystals, which provide the vast majority of the data available, are modulated by the crystal field effects and any one observation is therefore not necessarily representative of the potential energy minima of the isolated hydrogen-bonded adducts. 

It provides information about the geometry isolated hydrogen bonded dimer. It also provides information about the strength of the dimer. 

Information about nearly isolated hydrogen bonded dimers can be obtained by matrix-isolation techniques, which provide information on the geometries and energy for hydrogen bonded dimers frozen in an inert matrix [40, 41],... 

A molecule adsorbed at an isolated hydrogen bond donor site should diffuse less readily than it might on a surface with many such sites close together, where potential energy minima begin to overlap. Thus in all instances but one, the radical efficiency was lower on the Hq dehydroxy lated silica than on H, silica. The apparent exception was a photolysis, in which the radical efficiency is already low for other reasons. Covering part of the surface with azobenzene also appeared to decrease f, possibly because azocumene blocks some of the hydroxy 1-rich diffusion paths. 

Hydrogen Transfer in Isolated Hydrogen Bonded Molecules, Complexes and Clusters... 

Hydrogen bonds of terminal alkynes can have very different functions in hydrogen bond networks. Very simple ones are isolated hydrogen bonds of the types. 

The assumption of a strict, vapor-phase derived pair potential appears acceptable only in those cases where a weak intermolecular interaction does not cause appreciable structural relaxations in the monomers. In the case of hydrogen-bonded systems, the use of the frozen monomer assumption precludes, however, almost always the investigation of all the observable structural and spectroscopic features of the A—H moiety. Therefore, the reference system for the discussion of cooperative, nonadditive effects is exclusively the structurally fully optimized hydrogen-bonded dimer with a single isolated hydrogen bond and with all the properties derivable from the global 3N-6 dimensional potential energy surface of the dimer. 

Another point that requires furtlier research is the cooper-ativity effect. In a long. sequence of donor-acceptor-donor-acceptor.. . interactions, as found in most crystalline carbohydrates. cooperativity is thought to confer a higher strength (and shorter H O distances) on the individual bonds than would apply to isolated hydrogen bonds. Current modeling... 

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