One-bond Couplings to Hydrogen

The dependence of the 7hd coupling in HD on the interatomic distance R in the presence of an external magnetic field has been studied by Vizioli et al. A disappearance of the PSO, DSO and SD terms with the increasing distance has been observed. 

Effects of temperature and isotopic substitution on a /hh coupling in the cationic ruthenium complex [Cp Ru(dppm)(H2)] have been studied by Law 

An analysis of the solvent dependence of the A c and /hh couplings combined with an analysis of the changes in the IR first overtone carbonyl bond intensities and theoretical calculations allowed Abraham and co-workers to determine directly the conformational equilibria in 2-bromocyclo-hexanone, a model compound, by the use of which the authors illustrated an improved method of conformational analysis of substituted cyclohexanones. 

The effect of the substitution on S( H), 6( C) NMR chemical shifts and /hc couplings in heparin derivatives containing various sulfation patterns has been studied by Yates et al. They have observed that the /hc couplings at the glycosidic linkage positions varied between free-amino and A-sulfated compounds, by up to 9 Hz, indicating that an overall conformational change takes place upon sulfonation of the compounds. 

Afonin and co-workers have continued their interesting studies on the application of /hc couplings on the steric and electronic properties of heteroaromatic compounds. Recently, they have published the H and NMR data obtained for a series of 2-(pyridyl)pyrroles which have been shown to exist as two conformers with syn and anti arrangement of the heterorings. 

Concentration- and temperature-dependent NMR, IR and dipole moment studies on 4-N,N-dimethylamino-l,l,l-trifluoro-3-buten-2-one and two of its higher homologues performed by Wojcik et al. showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel closed dimers are formed with a network of improper intermolecular C-H O hydrogen bonds which causes an increase of Jhc by 1.5 Hz. 

The potential energy and spin-spin coupling surface of the simplest carbohydrate, glycolaldehyde, have been studied by Ratajczyk et at the second-order 

Moller-Plesset (MP2) level of theory. They have also studied the conformational dependence of the indirect C-H and C-C couplings including those across one and more bonds by means of DFT using the B3LYP functional. 

The application of /hc couplings in conformational analysis of six-membered heterocycles has been shortly overviewed by Juaristi et al. and by Alabugin et a/. The couplings have been also shortly addressed by Ribeiro and Rittner in their work on the role of hyperconjugation in the conformational analysis of methylcyclohexane and methylheterocyclohexanes. 

The electronic structure of 11 sparteines has been studied by Galasso et a/. by the use of experimental and DFT calculated NMR parameters, special attention being paid to spin-spin couplings. In particular, the influence of stereoelectronic hyperconjugative effects on A JMCeq/Vncax has been correctly accounted for by the DFT results. 

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One-bond couplings to hydrogen depend on hybridization and electronegativity. Thus the y( N, H) values for NHt 0=C(NH2), and HC = NH are 73.3. 89.0. and 134.0 Hz. respectively. One-bond couplings to C also show a reasonable correlation with hybridization. The magnitudes of one- and two-bond couplings to C are often comparable. 

One-bond coupling constants JCH may suffer from slight solvent effects. Table 3.4 shows this behavior for chloroform, whose carbon-proton coupling increases with the polarity of the medium when measured in different solvents, being 208 Hz in cyclohexane and 215 Hz in pyridine [92]. This is attributed to association between chloroform and solvents susceptible to hydrogen bonding. 

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