Intra-molecular hydrogen bonding

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), ... 

Fig. 2 Schematic representation of cellulose structures in solution Part A shows the fringed micellar structure. Parts B and C show possible chain conformations of celluloses of different DP. For high molecular weight cellulose, C, intra-molecular hydrogen bonding is possible...

The absorption spectrum of TIN in methylcyclo-hexane/isopentane at 150 K is represented by curve I, Fig. k. Curve III shows the absorption spectrum of MT in hexane at 296 K. In unpolar solvents the intra-molecular hydrogen bond of TIN is still intact (curve... 

II). From this it must be concluded that the long-wavelength absorption of curve I is due to the intra-molecular hydrogen bond of TIN in unpolar solvents as the intensity of this band is reduced in polar solvents (curve II) and disappears completely in the spectrum of MT (without intramolecular hydrogen bond), curve III. Curve IVa represents the fluorescence and IVb the phosphorescence emission of both TIN and MT in... 

Figure 4.3 Inter- and intra-molecular hydrogen bonds of native cellulose.

The principle of the method is that once a substance crystallizes, the interconversion of the various conformers stops and so the crystals correspond to one discrete conformation or another. This has established, that 1,2-dichloroethane crystallises exclusively in the anti form, while ethylene chlorohydrin crystallizes in a gauche form because of intra molecular hydrogen bonding. But when the molecule crystallizes in two or more conformations, we say that it shows polymorphism. 

DSC studies have shown that modification alters thermal transition temperatures and the overall enthalpy (AHgei) associated with gelatinization (Tables 10.13 and 10.14). Upon hydroxypropylation, the reactive groups introduced into the starch chains are capable of disrupting the inter-and intra-molecular hydrogen bonds, leading to an increase in accessibility by water that lowers... 

On occasions it is desirable to investigate the spectroscopic properties of solutions at high dilution (i.e. 0.005 m), as for example in the study of inter- and intra-molecular hydrogen bonding of compounds containing hydroxyl groups. 

Fourier analysis of Model 2 is still in progress. However, from the above experiments it is clear that the intra-molecular hydrogen bond scheme in Klebsiella K8 polysaccharide does not have hydrogen bonds strengthening every glycosidic linkage. 

The molecular structure of polysaccharides from Klebsiella serotype K8 has been examined by X-ray diffraction and computer-aided molecular modeling. The most favorable molecular model was not the one which had the maximum number of intra-molecular hydrogen bonds. This result suggests that in the analysis one should not a priori choose the molecular model which has the largest number of intra-molecular hydrogen bonds. 

The favourable intra-molecular hydrogen-bonding between the oxime proton and the phenol oxygen atom will reduce or overcome liganddigand repulsion enthalpy terms normally involved in the formation of bis-chelate complexes. The integrity of this head-to-tail macrocyclic assembly is preserved in c/.v-octahcdral complexes which are formed in the presence of a, co-diamines. [66, 67]... 

Explanation by tbe Intra-Molecular Hydrogen Bond Concept... 

Some enamines have been shown to form inter- and intra-molecular hydrogen bonds in the solid state77. Thus, a-tetrahydropyrrolidinylidene-2 (44) and ethyl a-hexahydroaze-pirylidene acetate (45) have been shown to occur as / -enaminoesters of configuration Z in the solid state, i.e. the same configuration as they have in solution78. 

---