Quelltext der Seite Benutzer:JakobP/Isotopomers

{{Importartikel}}
{{distinguish|Isotopologue}}

'''Isotopomers''' or '''isotopic isomers''' are [[isomers]] with [[isotope|isotopic]] atoms, having the same number of each isotope of each element but differing in their positions. The result is that the molecules are either [[constitutional isomer]]s or [[stereoisomer]]s solely based on isotopic location.
For example, 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 constitutional isotopomers of [[propane]]. (''R'')- and (''S'')-CH<sub>3</sub>CHDOH  or (''Z'')- and (''E'')-CH<sub>3</sub>CH=CHD are examples of isotopic stereoisomers of [[ethanol]] and of [[propene]], respectively.<ref>{{GoldBookRef|title=isotopomer|url=http://goldbook.iupac.org/I03352.html}}</ref>

==<sup>13</sup>C-NMR==
In [[nuclear magnetic resonance spectroscopy]], the highly abundant <sup>12</sup>C isotope does not produce any signal whereas the comparably rare <sup>13</sup>C isotope is easily detected. As a result, carbon isotopomers of a compound can be studied by [[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% [[Natural abundance|abundance]] of <sup>13</sup>C, so there is only about a 1% abundance of the total of the singly-substituted [[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 [[J-coupling|coupling effect]] between them as well as signals for each one itself. The [[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, a rate effect is sometimes observed between different isotopomers of the same chemical. This [[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|url= 
http://www.princeton.edu/~mjjr/mech.pdf}}</ref>

In 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 times.{{citation needed|date=March 2012}} This is because naturally occurring [[carbon dioxide]] contains both <sup>12</sup>C and <sup>13</sup>C. [[Monocotyledon|monocots]], such as [[rice]] and [[oat]]s, differ from [[Dicotyledon|dicots]], such as [[potato]]es and [[Fruit tree|tree fruit]]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]]. 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]]s of the subjects of the investigations.

==See also==
*[[Mass (mass spectrometry)]]
*[[Isotopologue]]

==References==
{{reflist}}
<nowiki>
[[Category:Physical chemistry]]
[[Category:Isomerism]]</nowiki>