Isotopomers

Isotopomers (isotopic isomers) are isomers having the same number of each isotopic

Isotope

Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...

 atom but differing in their positions. For example, CH₃CHDCH₃ and CH₃CH₂CH₂D are a pair of constitutional isotopomers. An isotopomer should not be confused with an isotopologue

Isotopologue

Isotopologues are molecules that differ only in their isotopic composition. Simply, the isotopologue of a chemical species has at least one atom with a different number of neutrons to the parent....

.

The peaks seen in a ¹³C NMR spectrum are a result of different Isotopomers.

Isotopomers (isotopic isomers) are isomers having the same number of each isotopic

Isotope

Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...

 atom but differing in their positions. For example, CH₃CHDCH₃ and CH₃CH₂CH₂D are a pair of constitutional isotopomers. An isotopomer should not be confused with an isotopologue

Isotopologue

Isotopologues are molecules that differ only in their isotopic composition. Simply, the isotopologue of a chemical species has at least one atom with a different number of neutrons to the parent....

.

¹³C NMR

The peaks seen in a ¹³C NMR spectrum are a result of different Isotopomers. For example consider ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...

 (CH₃CH₂OH). Ethanol will have 2 simple isotopomers one in which the ¹³C atom is on the methyl group i.e. ¹³CH₃CH₂OH and one isotopomer in which the ¹³C atom is on the methylene

Methylene

Methylene is a chemical species in which a carbon atom is bonded to two hydrogen atoms. Three different possibilities present themselves:* the −CH₂− group, e.g. dichloromethane...

 i.e. CH₃¹³CH₂OH.

This gives rise to 2 peaks in the ¹³C NMR spectrum.

Note the ¹²C atoms do not show up in the ¹³C NMR.

Also given that ¹³C is only present in 1% abundance, there is a very small chance of also seeing the isotopologue

Isotopologue

Isotopologues are molecules that differ only in their isotopic composition. Simply, the isotopologue of a chemical species has at least one atom with a different number of neutrons to the parent....

 in the ¹³C NMR, wherein both carbon atoms are ¹³C atoms (i.e. ¹³CH₃¹³CH₂OH). These atoms would couple

J-coupling

J-coupling is the coupling between two nuclear spins due to the influence of bonding electrons on the magnetic field running between the two nuclei. J-coupling contains information about dihedral angles, which can be estimated using the Karplus equation...

, giving satellites off the main peaks in a normal ¹³C-NMR spectrum and forming the basis for INADEQUATE (¹³C–¹³C correlation) experiments.

Uses

Isotopmers have been used to determine reaction pathways e.g. A m-Benzyne to o-Benzyne Conversion Through a 1,2-Shift of a Phenyl Group. Blake, M. E.; Bartlett, K. L.; Jones, M. Jr. J. Am. Chem. Soc. 2003, 125, 6485