Hydrogen bonding comparisons

HO-6 group by a hydrogen bond. Comparison of intermolecular contacts of the substituent group indicates that the (S)-2-hydroxypropyl group is better fitted to the cavity than the (i )-2-hydroxy-propyl group. 

Typically, this approach leads to a large number of possible structures, because Jones allowed both the 0-3 -0-5 and 0-2-0-6 type of intra molecular hydrogen bond. Comparison of the most plausible structures for cellulose I and II with observed equatorial and meridional intensity led Jones to conclude that several structures, including that of Meyer and Misch, are fair approximations to the actual structure, but none of them show especially good agreement with the x-ray intensities observed. As a possible solution, Jones suggested a statistical structure, in which there is randomness of chain polarity, but in which adjacent chains have one characteristic shift along the b axis when they have parallel orientation, and a different one for the antiparallel situation. 

Gordy W, Stanford SC (1941) Spectroscopic evidence for hydrogen bonds comparison of proton-attracting properties of liquids. III. J Chem Phys 9 204-214... 

Hydrogen bonds between —OH groups are stronger than those between —NH groups as a comparison of the boiling points of water (H2O 100 C) and ammonia (NH3 —33 C) demonstrates... 

As already mentioned molecules cohere because of the presence of one or more of four types of forces, namely dispersion, dipole, induction and hydrogen bonding forces. In the case of aliphatic hydrocarbons the dispersion forces predominate. Many polymers and solvents, however, are said to be polar because they contain dipoles and these can enhance the total intermolecular attraction. It is generally considered that for solubility in such cases both the solubility parameter and the degree of polarity should match. This latter quality is usually expressed in terms of partial polarity which expresses the fraction of total forces due to the dipole bonds. Some figures for partial polarities of solvents are given in Table 5.5 but there is a serious lack of quantitative data on polymer partial polarities. At the present time a comparison of polarities has to be made on a commonsense rather than a quantitative approach. 

A comparison of phenol acidity in DMSO versus the gas phase also shows an attenuation of substituent effects, but not nearly as much as in water. Whereas the effect of ubstituents on AG for deprotonation in aqueous solution is about one-sixth that in the gas phase, the ratio for DMSO is about one-third. This result points to hydrogen bonding of the phenolate anion by water as the major difference in the solvating properties of water and DMSO. ... 

The structure of malonyl-a-aminopyridine (cf. 121) has been discussed by Snyder and Robinson/ who interpreted the infrared and ultraviolet spectra and the fact that it could be converted into a monochloro derivative (122, R = Cl) to indicate that the intra-molecularly hydrogen-bonded hydroxy form 122 (R = OH) was predominant. However, comparison of the basicities of the methoxy compound 122 (R = OMe), the mesomeric betaine 123 (R = Me), and the parent compound indicates that in aqueous solution the last exists mainly in the zwitterion form 123 (R = H), ... 

In 1951, pyrid-4-thione was concluded from ultraviolet spectral data to exist predominantly as such in ethanolic solution,but no comparisons were made and this conclusion had to be considered as tentative. Pyrid-2-thione has been shown by X-ray crystallography to exist as hydrogen-bonded dimers (201) in the solid state, the posi-... 

---