Vicinal proton-coupling constants

In numerous complex aldol adducts it is not always possible to extract the relevant vicinal proton coupling constants. Heathcock and co-workers have recently noted that for the -hydroxy ketones and esters that exist in the preferred hydrogen-bonded conformations A and A, NMR spectroscopy may be conveniently employed to assign stereochemistry (13). 

In oxepino- and azepinotropones 156, the vicinal proton coupling constants are comparable to those of the monocyclic constituents. Thus, 1H-NMR spectroscopy reveals that the heterocyclic rings maintain a boat conformation while the tropone moieties remain almost planar (88CL1647 90CL91). 

In 2,3-dihydro-1,4-dioxin, -1,4-oxathiin, and -1,4-dithiin derivatives and their benzo analogues, the values of the vicinal proton coupling constant ratios and ring dihedral angles were determined and found to be consistent with half -chair conformation <820MR(18)92>. 

Bruckner et al. have further developed the double Fourier expansion treatment of unperturbed polypropylene chains of iso-, syndio-, and intermediate tacticities, incorporating vicinal proton coupling-constant data into the analysis by the standard use of straight matrix correlation products for the estimation of rotational angle probabilities. To include non-bonded interactions arising between carbon atoms separated by more than four bonds, the repulsive term of the force field was enhanced to provide an improved interpretation of the experimental data. 

Grindley and Szarek have deduced the conformations of the seven-membered ring in 2,5-G-methylene- and l,3 2,5-di-0-methylene-D-mannitoland 1,6-di-0-benzyl-2,5-0-methylene-D- raZ)/ o-hex-3-ulose in solution from the geminal and vicinal proton coupling constants. 

In a linear chain, the n -1-1 Rule is strictly obeyed only if the vicinal proton coupling constants CJ) are exactly the same for every successive pair of carbons. 

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