Some stereochemical aspects of two-bond ¹³C–¹H spin–spin coupling. Sign determination in natural abundance ¹³C nuclear magnetic resonance spectra

Abstract

The magnitudes and signs of two-bond 13C–1H coupling constants (2J) in the array O—13CA—CB—1H, appear to be determined by the relative orientations of the O—13CA and CB—1H bonds, as shown with a variety of carbohydrate derivatives. The data have been observed from natural abundance lH-coupled 13C nmr spectra, and signs of 2J have been determined by the 'selective population transfer' technique. When CB bears one oxygen atom, the observed 2J values range from −6 to 0 Hz, whereas a range of 0 to +8 Hz is found when CB bears two oxygen atoms. By contrast, for arrays in which CB bears one oxygen atom and CB two, the 2J values vary from −6 to +6 Hz. In general, the results confirm earlier indications that the larger the torsional angle between the O—13CA and CB—1H bonds, the more positive is the value of 2J. These findings are supported by calculations for model compounds, i.e., propane-1,1,2-triol and butane-2,3-diol.

Complete structure of the polysaccharide from Streptococcus sanguis J22

“…The reported values of long-range 13C-'H coupling constants for D-mannose were used to interpret intraresidue long-range 13C-'H correlation data on L-Rha because these sugars have the same relative stereochemistry. As a model for the GalNAc residues, the reported values for galactose may not reflect the actual value of geminal CH couplings involving the C-2 atom due to perturbatons of the amide substituent (Cyr et al, 1978). Although the cross-peak intensity was not strictly proportional to the magnitude of the heteronuclear coupling constants involved, all the peaks except those arising from glycosidic linkages and the Gal/ residue can be explained by reported VCH values.…”

Effect of oxygen substituents on two- and three-bond carbon-proton spin-spin coupling constants

“…It was first noted in an experimental study of carbohydrates and a theoretical study of ethanol and 1,1-ethanediol 33 that, in the case of synclinal and antiperiplanar arrangements of the˛-oxygen, the 2 J( 13 C, 1 H coupling constant has a negative and a positive sign, respectively. This finding has been cited and applied as a general rule 34 for 2 J( 13 C, 1 H) despite the same authors publishing a theoretical study for hydroxylated propanes 35 to show that the oxygen at Cˇshould also be considered when predicting the value and the sign of 2 J( 13 C, 1 H). By an other approach, a general recipe was given to estimate the 2 J( 13 C, 1 H) coupling constants in carbohydrates.…”

Long‐range protoncarbon‐13 coupling constants of monosaccharides by selective heteronuclear 2D‐J NMR spectroscopy

“…I), a selective 180" proton pulse is used when observing the 13C signal by spin-echo so as to affect only the long-range 'H-13C couplings with the selected proton. 1. Selective 2D-J heteronuclear pulse sequence according to Bax and Freeman.'…”