Hydrogen bonding direct perturbation

Directional properties of acceptor groups are very soft or nonexistent. Just as the H A lengths and X-ft- -A angles for individual hydrogen bonds are perturbed by the other intermolecular forces in the crystal, so are the directional acceptor properties of the functional groups. These properties appear to be even softer than the hydrogen-bond geometries, and in consequence it is not possible to extract any characteristic trends from the surveys of the type described in this chapter. 

First and foremost, the redox couple must be reversible, meaning relatively fast electron transfer reactions and products that are stable in both oxidation states. As discussed previously, for systems in which the hydrogen bonds are to be directly perturbed, the redox reaction must affect the charge distribution on the atoms involved... 

It is interesting to study the structural properties of the neat hydrogen-bonded liquid without the perturbing influence of apolar molecules in mixtures. As an example in this direction the dynamics of ethanol in the isotopic mixture are investigated. Data will be presented on ethanol-d6 samples containing 1 vol% (diluted) or 50 vol% (concentrated) of protonic ethanol (88). In contrast to the apolar CCU environment, additional H bonds between the ethanol molecules and their environment can be formed representing new species with modified properties. 

Thus we are led to admit that in certain cases hydrogen bond formation can be monitored by intensity changes only but the question still remains if in actual associations the Cl atoms or C—Cl bonds are directly perturbed or only suffer the indirect effect of the perturbation of the H atoms or C—H bonds. In order to clarify this we first carried out low temperature and then room temperature work on CH Clj and similar molecules. 

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