Carbon-13 NMR satellite

Carbon satellites are small peaks that can be seen shouldering the main peaks in an NMR spectrum. These peaks can occur in the NMR spectrum of any NMR active atom (e.g. ¹⁹F or ³¹P NMR) where those atoms adjoin a carbon atom (and where the spectrum is not ¹³C-decoupled, which is usually the case). However, Carbon satellites are most often encountered in proton NMR.

In the example of proton NMR, these peaks are not the result of proton-proton coupling, but result from the coupling of ¹H atoms to an adjoining ¹³C atom. These small peaks are known as carbon satellites as they are small and appear around the main ¹H peak i.e. satellite (around) to them. Carbon satellites are small because ¹³C only makes up about 1% of the atomic carbon content of carbon, the rest of the carbon atoms are predominantly NMR inactive ¹²C. Carbon satellites always appear as an evenly spaced pair around the main ¹H peak. This is because they are the result of 1% of the ¹H atoms coupling to an adjoined ¹³C atom to give a wide doublet (¹³C has a spin of a half). Note, if the main ¹H-peak has proton-proton coupling, then each satellite will be a miniature version of the main peak and will also show this ¹H-coupling, e.g. if the main ¹H-peak is a doublet, then the carbon satellites will appear as miniature doublets, i.e. one doublet on either side of the main ¹H-peak.

For other NMR atoms (e.g. ¹⁹F or ³¹P atoms), the same applies as above, but obviously where the proton atom is replaced with that other NMR active atom e.g. ³¹P.

Sometime other peaks can be seen around ¹H peaks, these are known as spinning sidebands and are related to the rate of spin of an NMR tube.

Carbon satellites (and spinning sidebands) should not be confused with impurity peaks.

Uses

Cis-Stilbene

Trans-Stilbene

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.^[1]

See also

• not to be confused with side band spinning effect,
• ¹H NMR
• ¹³C NMR

References

1. Harald. Gunther (Jul 1995). NMR Spectroscopy: Basic principles, concepts, and applications in chemistry (second ed.). John Wiley & Sons. pp. 214–219. ISBN 0-471-95201-X.

Further reading

• NMR SATELLITES AS A PROBE FOR CHEMICAL INVESTIGATIONS SHIzuo FUJIWARA, Yogi ARATA, HIR0sHI OZAWA and MASAYUKI KuruGI Department of Chemistry, The University of Tokyo, Japan
• Y. Ogimura, S. Fujiwara and K. Nagashima, Chemical Instrumentation 1, 21 (1968); S. Fujiwara, Y. Yano and K. Nagishima, Chemical Instrumentation 2, 103 (1969); S. Fujiwara, Magnetic Resonance, ed., C. K. Coogan et a!., Plenum Press, New York (1970).
• H. Ozawa, Y. Arata and S. Fujiwara, J. Chem. Phys., to be published.
• S. Forsén and R. A. Hoffman, J. Chem. Phys. 40, 1189 (1964); R. A. Hoffman and S. Forsén, J. Chem. Phys. 45, 2049 (1966).
• N. Bloembergen and R. V. Pound, Phys. Rev. 95, 8 (1954); S. Bloom, J. App!. Phys. 28, 800 (1957).
• A. O. Niel, Phys. Rev. 77, 789 (1950).
• Geometry determination of tetrasubstituted stilbenes by proton NMR spectroscopy, Viviana S. Fluxáa, Titus A. Jennya and Christian G. Bochet, Tetrahedron Letters, Volume 46, Issue 22, 30 May 2005, Pages 3793-3795