Carbon coupling constants influence

Marshall and Ihrig (62) have also examined the influence of ring substituents on carbon-carbon coupling constants in a number of o- and p-substituted toluenes (13CH3). The results are presented in Table IV... 

H and 13C NMR Data. The examples in Scheme 3.3 provide insight into expected proton and carbon chemical shift and coupling constant data for primary alkyl fluorides. It can be seen that the influence on both proton and carbon chemical shifts diminishes rapidly as one moves away from the site of fluorine substitution. 

The influences of SF5 groups upon H and 13C NMR spectra are also quite characteristic, and information about proton and carbon chemical shifts and the respective coupling constants will be included along with the 19F data where they are available. The proton and carbon NMR spectra for (pentafluorosulfanylmethylene)cyclohexane are provided in Figs. 7.3 and 7.4 as typical examples. 

The influence of substituents at phosphorus and carbon atoms on the equilibrium position of dioxaphosphorinanes and their derivatives is due to donor-acceptor interaction. Stereospeciflc coupling constants are found for 4,6-disubstituted dioxaphosphorinanes and the possibility of applying them to determine the spatial structure of isomers has been reported. 

Classical shielding arguments indicate an electron-rich phosphorus atom, or equally, an increase in coordination number. The silicon atom seems also to be electron-rich, while the carbon has a chemical shift in the range expected for a multiply bonded species. The coupling constant data are difficult to rationalize, as it is not possible to predict the influence of orbital, spin-dipolar, Fermi contact, or higher-order quantum mechanical contributions to the magnitude of the coupling constants. However, classical interpretation of the NMR data indicates that the (phosphino)(silyl)carbenes have a P-C multiple bond character. 

H,13C coupling constants through one bond are positive. The major structural influence is the carbon hybridization state, and its -character (s) can be estimated using the empirical correlation ... 

Intermolecular solvent-solute interactions influence the charge distribution on a carbohydrate molecule. Subtle electronic changes that occur as a result of these interactions are responsible for the solvent dependence of carbon -proton coupling constants. The general aspects of solvent effects on NMR parameters have been reviewed,78-79 and consequently, only a very brief outline of the theoretical model within FPT INDO SCF MO formalism is considered here. 

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