Hydrogen bonding—NMR

Keywords Heteroaromaticity, Hydrogen bonds, NMR, Proton transfer, Tautomerism... 

The Hydrogen Bond NMR Shift in Pure Substances. It has been a prophetic circumstance that the recognition of the H bond proton resonance chemical shift involved one of the pioneers of tfie IR study of the H bond (U. Liddel). The NMR H bond effect will undoubtedly be as informative as the IR frequency shifts. There are many similarities... 

The crystal structme of 28 showed that the compound adopts a pinched-cone conformation with the ethylene glycol substituents properly disposed to fold in and bind a metal cation at the base of the cahxarene and that the two thiourea units are effectively oriented to provide an anion-binding site through hydrogen bonding. NMR titrations in CD3CN of 28 with the TBA... 

Tjandra N and Bax A 1997 Solution NMR measurement of amide proton chemical shift anisotropy in N-15-enriched proteins. Correlation with hydrogen bond length J. Am. Chem. Soc. 119 8076-82... 

The entropy value of gaseous HCl is a sum of contributions from the various transitions summarized in Table 4. Independent calculations based on the spectroscopic data of H Cl and H Cl separately, show the entropy of HCl at 298 K to be 186.686 and 187.372 J/(mol K) (44.619 and 44.783 cal/(mol K), respectively. The low temperature (rhombic) phase is ferroelectric (6). SoHd hydrogen chloride consists of hydrogen-bonded molecular crystals consisting of zigzag chains having an angle of 93.5° (6). Proton nmr studies at low temperatures have also shown the existence of a dimer (HC1)2 (7). 

C NMR, 6, 398 molecular dimensions, 6, 397 tautomerism, 6, 404 Furoxan-3-carbohydra2ide intramolecular hydrogen bonding, 6, 396 Furoxan-3-carboxamide intramolecular hydrogen bonding, 6, 396 Furoxancarboxylic acids reactions, 6, 413 with nucleophiles, 6, 406 Furoxan-3,4-dicarbaldoxime synthesis, 6, 409 Furoxanoaaines fused... 

Pyridinium iodide, 4,4 (l,3,4-thiadiazole-2,5-diyl)-bis(l-methyl)-reduction, 6, 564 Pyridinium ion, Af-methyl-as metabolite of pyridine, 1, 234 Pyridinium ions hydrogen bonding to water mass spectrometry, 2, 135 magnetic circular dichroism, 2, 129 NMR, 2, 121... 

Einally, structural properties that depend directly neither on the data nor on the energy parameters can be checked by comparing the structures to statistics derived from a database of solved protein structures. PROCHECK-NMR and WHAT IE [94] use, e.g., statistics on backbone and side chain dihedral angles and on hydrogen bonds. PROSA [95] uses potentials of mean force derived from distributions of amino acid-amino acid distances. 

BW Beck, Q Xie, T Ichiye. Computational study of S—H S hydrogen bonds m [4Ee-4S]-type ferredoxm x-ray and NMR structures Characterization and implications for redox potentials. Protein Sci, submitted. 

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