View source for Nuclear magnetic resonance spectroscopy of stereoisomers

'''Nuclear magnetic resonance spectroscopy of stereoisomers''' most commonly known as '''NMR spectroscopy of stereoisomers''' is a [[chemical analysis]] method that uses [[NMR spectroscopy]] to determine the [[absolute configuration]] of [[stereoisomers]]. For example, the [[cis-trans isomerism|''cis'' or ''trans'']] [[alkene]]s, ''R'' or ''S'' [[enantiomer]]s, and ''R,R'' or ''R,S'' [[diastereomer]]s.<ref>David Parker. "NMR determination of enantiomeric purity." ''[[Chem. Rev.]]'' '''1991''', ''91'', 1441–1457. [http://pubs.acs.org/doi/abs/10.1021/cr00007a009]</ref><ref>Frank J. Hollis. "NMR Through the Looking Glass: Uses of NMR Spectroscopy in the Analysis and Synthesis of Chiral Pharmaceuticals." 1994. [http://homepage.ntlworld.com/chemist/s442.pdf]</ref>

In a mixture of enantiomers, these methods can help quantify the [[optical purity]] by integrating the area under the NMR peak corresponding to each stereoisomer.  Accuracy of integration can be improved by inserting a [[chiral derivatizing agent]] with a nucleus other than hydrogen or carbon, then reading the heteronuclear NMR spectrum: for example [[fluorine-19 NMR]] or [[phosphorus-31 NMR]].  [[Mosher's acid]] contains a -CF<sub>3</sub> group, so if the adduct has no other fluorine atoms, the <sup>19</sup>F NMR of a racemic mixture shows just two peaks, one for each stereoisomer.

As with NMR spectroscopy in general, good resolution requires a high [[signal-to-noise ratio]], clear separation between peaks for each stereoisomer, and narrow line width for each peak.  Chiral lanthanide shift reagents cause a clear separation of chemical shift, but they must be used in low concentrations to avoid [[line broadening]].

==Methods==
*[[Karplus equation]]
*[[Chiral derivatizing agent]]
**[[Mosher's acid]]
**Chiral solvating agent
**Chiral lanthanide shift reagent (e.g. [[Eufod]])
*[[NMR database method]]

==References==
{{reflist}}

==See also==
*[[Ultraviolet-visible spectroscopy of stereoisomers]]

{{chiral synthesis}}

[[Category:Nuclear magnetic resonance spectroscopy]]


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