Two-bond Couplings to Hydrogen

Geminal and vicinal proton-proton couplings have been collected and applied by Hughes et al in their studies on the structure of six alkaloids of the Lythraceae group, i.e. decinine, decodine, decamine, verticillatine, decaline and vertaline, and by Krajewski et who studied solution conformation of the alkaloid chelidonine and its protonated form. 

Differences in the proton-proton couplings of the N -CH2-CH2 protons of some betaines, N -(CH2) -COO ( = 2, 3), and their complexes in solutions have been analysed by Szafran et al in order to get insight into the conformations of the compounds studied. 

Two-bond proton-proton couplings of ca. 16 Hz have been reported by Suarez et al for a series of 1,4,5,6,7,8-hexahydroquinolines and their oxa-analogues 5,6,7,8-tetrahydro-4/f-chromenes. 

Structural and conformational investigation of two series of 2,4,6-tris(a-mino)-s-triazines by the use of H and C NMR including Vhh and Vhh couplings has been made by Amm et al  

A complete analysis of the higher-order H NMR spectra of dimethylpro-pylsilane, its alkyl analogue, 2-methylpentane, and dimethylethylsilane has been performed by Bain et al yielding two- and three-bond proton-proton couplings for these compounds. 

Fermi hole density functions have been computed by Soncini and Lazzeretti for the first-row hydrides. The relative maps have been compared with those of one- and two-bonds nuclear spin-spin coupling density. The interesting observation concerns geminal H-X-H coupling, which is determined mainly by the spin density near the heavy X nucleus. If it were not involved, no geminal coupling could arise. 

Geminal and vicinal H-H couplings have been measured by Guthrie et for new examples of 5-substituted-l-aza-4,6-dioxabicyclo[3.3.0]octanes(bicyclic amide acetals), and for some examples of the new heterocyclic system, 5-sub-stituted-l-aza-4-oxa-6-thiabicyclo[3.3.0]octanes (bicyclic amide mono-thioacetals). A detailed analysis of this data combined with the X-ray results allowed the authors to elucidate the stereochemistry and conformation of these ring systems. 

Geminal and vicinal proton-proton couplings have been measured by Rodriguez and Jimeno for a large series of naturally occurring diterpenoids and some synthetic derivatives the vicinal couplings have been applied to 

Isotope and solvent effects on fluxional hydrogen-bonded complexes of acetic acid and acetate have been studied by Limbach and co-workers. The spectra have been measured in the presence of tetra-n-butylammonium acetate around 110 K using liquefied Freon mixture as a solvent. Also spectra of the adduct CHs COOH SbCb have been recorded for comparison. For the first time, a two-bond coupling of the type JiCUsCOOH) between a hydrogen-bonded proton and the carboxylic carbon has been observed, Jhc = 3.0 Hz for comparison, the corresponding Jhc value in CHs COOH SbCb equals to 6.7 Hz. 

DFT calculations of H-H and H-C couplings across two and three bonds and a simulation of 2D H homo- and H- C heteronuclear NMR spectra of organic molecules have been suggested by Biffulco et al. as a tool in the determination of the relative configuration of organic compounds. 

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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. 

Isotope effects have been used to provide information on the electronic transmission paths between the metal and the nuclei in first and second coordination spheres. Thus, the two-bond deuterium isotope effect A( H) on going from C5H5V(CO)4 to C5D5V(CO)4 (—0.75 ppm per has been discussed in terms of non-negligible overlap between hydrogen and metal orbitals [33]. The distinct two-bond coupling derived from relaxation... 

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