Carbon-13 NMR Satellite - Uses


Carbon satellites can be used to obtain structural information, which is not available by looking at the main peaks in the NMR spectrum.

This usually occurs when the purely 12C compound is symmetrical but where the 1% of the compound which has a 13C atom in it is no longer symmetrical.

For example, you can not tell if stilbene (Ph-CH=CH-Ph) has a cis- or trans- double bond just by examining at the main peaks in the 1H NMR spectrum. The =CH- proton does not couple to the adjacent =CH- proton as the molecule is symmetrical. However 1% of the stilbene molecules will have a 13C atom on one of these double bond carbons (i.e. Ph-13CH=12CH-Ph). In this situation, the proton adjacent to 13C atom will couple to the 13C atom to give a wide doublet. Also, as this molecule is no longer symmetric the 13CH= proton will now couple to the adjacent 12CH= proton, causing a further doubleting. Thus this additional coupling (additional to the 13C coupling) is diagnostic of the type of double bond, and will allow one to determine if the stilbene molecule has a cis- or trans- configuration i.e. by examining the size of the diagnostic J coupling constant from -CH=CH- bond. Thus only a single 1H NMR spectrum is needed, albeit with close inspection of the satellite peaks, rather than any further complex NMR or derivative chemical experiments.

The same would be see for 1,2-Dichloroethene.

Read more about this topic:  Carbon-13 NMR Satellite

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