Proton nuclear magnetic resonance hydrogen bonding

The last two criteria, (4) and (5), are the most unequivocal and powerful signs for the formation of the hydrogen bond. A A-H) and IRa H bCKA—H))/ IRa h(KA—H)) are the most important characteristics of H-bonding, its fingerprints or signature [33], say literally. Proton nuclear magnetic resonance ( H NMR) chemical shifts in the A H- -B hydrogen bond are shifted downfield compared to the monomer,... 

In the early proton nuclear magnetic resonance ( H NMR) studies with the O2 complexes of amide functionalized, basket-handle porphyrins (5, Fig. 2), a pronounced downfield shift of the amide C(0)—NH was observed in apolar solvent, indicating the C(0)—NH 02 hydrogen bonding (14a,16). This hydrogen bond, however, was weak, since the estimated nitrogen-02 distance is 4 A. 

Proton chemical shift data from nuclear magnetic resonance has historically not been very informative because the methylene groups in the hydrocarbon chain are not easily differentiated. However, this can be turned to advantage if a polar group is present on the side chain causing the shift of adjacent hydrogens downfteld. High resolution C-nmr has been able to determine position and stereochemistry of double bonds in the fatty acid chain (62). Broad band nmr has also been shown useful for determination of soHd fat content. 

Abstract—Possible causes of the nuclear magnetic resonance shifts in hydrogen bonding are examined in a semi-quantitative manner, The total screening of the proton arises from the secondary magnetic field of the electronic currents induced by the applied external magnetic held. If the bonding system is denoted by X—H 5 e Y then two main possibilities have to be considered. 

Dega-Szafran, Z., Szafran, M., Stefaniak, L., Brevard, C., and Bourdonneau, M., Nitrogen-15 nuclear magnetic resonance studies of hydrogen bonding and proton transfer in some pyridine trifluoroacetates in dichloromethane, Magn. Reson. Chem., 24, 424, 1986. 

The formation of complexes containing hydrogen bonds is detected by the same methods as in the case of polyelectrolyte complexes. Moreover, spectroscopic methods such as Infrared, Raman and Nuclear Magnetic Resonance are used as efficient analytical methods. The composition of [proton-donating polymer unit]/[proton-accepting polymer unit] is generally 2/1 to 2/3 in dilute... 

Altman, L. J., Lauggani, D., Gunnarsson, G., and Wennerstrom, H., Proton, deuterium, and tritium nuclear magnetic resonance of intramolecular hydrogen bonds. Isotope effects and the shape of the potential energy function, J. Am. Chem. Soc. 100, 8264-8266 (1978). 

L. Poppe and H. van Halbeek, Nuclear magnetic resonance of hydroxyl and amido protons of oligosaccharides in aqueous solution. Evidence for a strong intramolecular hydrogen bond in sialic acid residues, J. Am. Chem. Soc., 113 (1991) 363-365. 

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