Is their any relation between the J-coupling constant and the geometry of molecules? I have a molecule: 1,3-Oxazepine 4,7-dione derivatives and it has chiral center. I would like to determine if it has R or S configuration and was wondering if I could do so by using the J-coupling constant? If so, how?
Could you make a sketch of example derivative? How many stereocentres does it have? It is important while only relative configuration can be sometimes elucidated by calculating torsion angles from H-H 3J-coupling constants.
The coupling constant J will give you only the relative stereochemestry and not the absolute configuration R or S.
If you have only one chiral center in your molecule, then you cannot distinguish R/S absolute configurations by simple NMR spectroscopy, since two enantiomers will have identical spectra. J-coupling can only allow you to assign the relative configuration (cis/trans or E/Z) to diastereomers, i.e. when you have two or more chiral centers.
If you want to assign the R/S absolute configuration to your compounds you will have to use chiroptical spectroscopies like circular dichroism, or perform NMR with chiral shift reagents.
Yoiu can use J values to determine the configuration of a single stereogenic center in a molecule. If the molecule has more than one stereogenic center and you know the configuration of one of them, maybe you could be able to deduct the configuration of the seocnd one from your data. If you do not have this info or if you have a single stereogenic center, then this approach will be unsuccessful. You may use chiral reagents and prepare derivatives or use chiral shift reagents and make comparisons.
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