# Isotopomer

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{{Short description|Molecules with same isotopes in different positions}}
{{distinguish|Isotopologue}}

350 px|thumb|Isotopomers of isotopically modified ethanol. The molecule at the bottom left is not an isotopomer of any other depicted molecule.
'''Isotopomers''' or '''isotopic isomers''' are [isomer](/source/isomer)s which differ by [isotopic substitution](/source/isotope), and which have the same number of atoms of each isotope but in a different arrangement. For example, CH<sub>3</sub>OD and CH<sub>2</sub>DOH are two isotopomers of monodeuterated [methanol](/source/methanol).

The molecules may be either [structural isomer](/source/structural_isomer)s (constitutional isomers) or [stereoisomer](/source/stereoisomer)s depending on the location of the isotopes. Isotopomers have applications in areas including [nuclear magnetic resonance spectroscopy](/source/nuclear_magnetic_resonance_spectroscopy), [reaction kinetics](/source/reaction_kinetics), and [biochemistry](/source/biochemistry).

== Description ==
Isotopomers or isotopic isomers are [isomer](/source/isomer)s with [isotopic](/source/isotope) atoms, having the same [number](/source/Mass_number) of each isotope of each [element](/source/Chemical_element) but differing in their positions in the molecule. The result is that the molecules are either [constitutional isomer](/source/constitutional_isomer)s or [stereoisomer](/source/stereoisomer)s solely based on isotopic location. The term isotopomer was first proposed by [Seeman](/source/Jeffrey_I._Seeman) and Paine in 1992 to distinguish isotopic isomers from [isotopologue](/source/isotopologue)s (isotopic homologues).<ref name="Seeman">{{cite journal |last1=Seeman |first1=Jeffrey I. |last2=Secor |first2=Henry V. |last3=Disselkamp |first3=R. |last4=Bernstein |first4=E. R. |date=1992 |title=Conformational analysis through selective isotopic substitution: supersonic jet spectroscopic determination of the minimum energy conformation of o-xylene |journal=Journal of the Chemical Society, Chemical Communications |issue=9 |page=713 |doi=10.1039/C39920000713}}</ref><ref>{{cite journal |last1=Seeman |first1=Jeffrey I. |last2=Paine, III |first2=J. B. |date=December 7, 1992 |title=Letter to the Editor: 'Isotopomers, Isotopologs' |journal=Chemical & Engineering News |publisher=American Chemical Society |volume=70 |issue=2 |doi=10.1021/cen-v070n049.p002 |doi-access=free}}</ref>

== Examples ==
* CH<sub>3</sub>CHDCH<sub>3</sub> and CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>D are a pair of structural isotopomers of [propane](/source/propane).
* (''R'')- and (''S'')-CH<sub>3</sub>CHDOH  are isotopic stereoisomers of [ethanol](/source/ethanol).
* (''Z'')- and (''E'')-CH<sub>3</sub>CH=CHD are examples of isotopic stereoisomers of [propene](/source/propene).<ref>{{GoldBookRef|title=isotopomer|file=I03352}}</ref>

== Use ==

=== <sup>13</sup>C-NMR ===
In [nuclear magnetic resonance spectroscopy](/source/nuclear_magnetic_resonance_spectroscopy), the highly abundant [<sup>12</sup>C](/source/Carbon-12) isotope does not produce any signal whereas the comparably rare [<sup>13</sup>C](/source/Carbon-13) isotope is easily detected. As a result, [carbon](/source/carbon) isotopomers of a compound can be studied by [carbon-13 NMR](/source/carbon-13_NMR) to learn about the different carbon atoms in the structure. Each individual structure that contains a single <sup>13</sup>C isotope provides data about the structure in its immediate vicinity. A large sample of a chemical contains a mixture of all such isotopomers, so a single spectrum of the sample contains data about all carbons in it. Nearly all of the carbon in normal samples of carbon-based chemicals is <sup>12</sup>C, with only about 1% [abundance](/source/Natural_abundance) of <sup>13</sup>C, so there is only about a 1% abundance of the total of the singly-substituted [isotopologue](/source/isotopologue)s, and exponentially smaller amounts of structures having two or more <sup>13</sup>C in them. The rare case where two adjacent carbon atoms in a single structure are both <sup>13</sup>C causes a detectable [coupling effect](/source/J-coupling) between them as well as signals for each one itself. The [INADEQUATE](/source/INADEQUATE) correlation experiment uses this effect to provide evidence for which carbon atoms in a structure are attached to each other, which can be useful for determining the actual structure of an unknown chemical.

=== Reaction kinetics ===
In [reaction kinetics](/source/reaction_kinetics), a rate effect is sometimes observed between different isotopomers of the same chemical. This [kinetic isotope effect](/source/kinetic_isotope_effect) can be used to study reaction mechanisms by analyzing how the differently massed atom is involved in the process.<ref>{{Cite journal|doi=10.1021/ja0213672|pmid=12785789|title=A ''m''-Benzyne to ''o''-Benzyne Conversion through a 1,2-Shift of a Phenyl Group|journal=Journal of the American Chemical Society|volume=125|issue=21|pages=6485–6490|year=2003|last1=Blake|first1=Michael E.|last2=Bartlett|first2=Kevin L.|last3=Jones|first3=Maitland|bibcode=2003JAChS.125.6485B |url=
http://www.princeton.edu/~mjjr/mech.pdf}}</ref>

=== Biochemistry ===
In [biochemistry](/source/biochemistry), differences between the isotopomers of biochemicals such as starches is of practical importance in archaeology. They offer clues to the diet of prehistoric humans that lived as long ago as [Paleolithic](/source/Paleolithic) times.{{citation needed|date=March 2012}} This is because naturally occurring [carbon dioxide](/source/carbon_dioxide) contains both <sup>12</sup>C and <sup>13</sup>C. [Monocots](/source/Monocotyledon), such as [rice](/source/rice) and [oat](/source/oat)s, differ from [dicots](/source/Dicotyledon), such as [potato](/source/potato)es and [tree fruit](/source/Fruit_tree)s, in the relative amounts of <sup>12</sup>CO<sub>2</sub> and <sup>13</sup>CO<sub>2</sub> that they incorporate into their tissues as products of [photosynthesis](/source/photosynthesis). When tissues of such subjects are recovered, usually tooth or bone, the relative isotopic content can give useful indications of the main source of the [staple food](/source/staple_food)s of the subjects of the investigations.

==Cumomer==
A '''cumomer''' is a set of isotopomers sharing similar properties and is a concept that relates to [metabolic flux analysis](/source/metabolic_flux_analysis). The concept was developed in 1999.<ref name=Wiechert99>{{cite journal | vauthors = Wiechert W, Möllney M, Isermann N, Wurzel M, de Graaf AA | title = Bidirectional reaction steps in metabolic networks: III. Explicit solution and analysis of isotopomer labeling systems | journal = Biotechnology and Bioengineering | volume = 66 | issue = 2 | pages = 69–85 | date = 1999 | doi = 10.1002/(SICI)1097-0290(1999)66:2<69::AID-BIT1>3.0.CO;2-6 | pmid = 10567066 }}</ref><ref>{{cite journal | vauthors = Yang TH, Frick O, Heinzle E | title = Hybrid optimization for 13C metabolic flux analysis using systems parametrized by compactification | journal = BMC Systems Biology | volume = 2 | issue = 1 | article-number = 29 | date = March 2008 | pmid = 18366780 | pmc = 2333969 | doi = 10.1186/1752-0509-2-29 | doi-access = free }}</ref> In a metabolic cascade, many molecules will contain the same pattern of isotope labelling. In order to simplify the analysis of such cascades, molecules with identically labelled atoms are aggregated into a virtual molecule called a ''cumomer'' (a conflation of ''cumulative'' and ''isotopomer'').<ref name=Wiechert99/>

==See also==
* [Mass (mass spectrometry)](/source/Mass_(mass_spectrometry))
* [Isotopocule](/source/Isotopocule)

==References==
{{reflist}}

== Further reading ==
* {{cite book | vauthors = Yang TH | title = Systems Metabolic Engineering | chapter = <sup>13</sup>C-Based Metabolic Flux Analysis: Fundamentals and Practice | series = Methods in Molecular Biology | location = Clifton, N.J. | publisher = Humana Press | volume = 985 | pages = 297–334 | date = 2013 | pmid = 23417810 | doi = 10.1007/978-1-62703-299-5_15 | isbn = 978-1-62703-298-8 }}

Category:Physical chemistry
Category:Isomerism

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Adapted from the Wikipedia article [Isotopomer](https://en.wikipedia.org/wiki/Isotopomer) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Isotopomer?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.