Isotopomers are isomers which have the same isotopic composition, but the place they occur in the molecule differs. Isotopes are atoms of the same species, but they differ in the number of neutrons in the nucleus. The term is a contraction of isotopic isomers.

An example of structural isotopomers are the deuterated variants of propane: CH3CHDCH3 and CH3CH2CH2D. In the first case, the deuterium is on the middle carbon atom, while in the second structure the deuterium is in the terminal methyl group. There are also stereo isotopomers.

Isotopomers can be used to detect a particular reaction mechanism because the atoms can be followed in their displacements during a reaction. Isotopomerism in NMR

Isotopomerism is of major importance in NMR, with the various peaks seen in the C-spectrum being a result of the different position that the C-isotope can take in a molecule. An example is ethanol (CH 3 CH 2 OH), in which 2 carbon atoms are present: one in the methyl group (CH 3) and one in the methylene group (CH 2). These two carbon atoms can be both C and C. However, C is an NMR-inactive isotope, which implies that only the C signals will be included. This results in 2 peaks in the spectrum. Also see

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