Isotopomers
Encyclopedia
Isotopomers or isotopic isomers are isomers with isotopic
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 atoms, having the same number of each isotopic atom but differing in their positions. It can be either constitutional isomers or stereoisomers.
For example, CH3CHDCH3 and CH3CH2CH2D are a pair of constitutional isotopomers. (R)- and (S)-CH3CHDOH or (Z)- and (E)-CH3CH=CHD are examples of isotopic stereoisomers.


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 than 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 and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 (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- substituent 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 than 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

Isotopomers 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
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