Differentiation of meso isomers from racemic mixtures with the combined use of chiral shift reagents and two-dimensional heteronuclear correlation NMR spectroscopy
✍ Scribed by P. Mark Henrichs; Charles A. Rodger; Thomas Caulfield; Peng Guo
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 278 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
In the presence of chiral shift reagents the enantiotopic nuclei of a pair of enantiomers become diastereotopic and have the potential to give resolved NMR signals. Similarly, the enantiotopic nuclei within a meso isomer become diastereotopic in the presence of a chiral shift reagent and may give resolved NMR signals. However, the diastereotopic nuclei of a meso isomer mixed with a chiral shift reagent, unlike those of a racemic mixture, are located in the same molecule. Their intramolecular character can be established experimentally by detection of spin‐spin splitting between them or to a common third nucleus. Comparison of the correlation peaks in a two‐dimensional, heteronuclear, multiple‐quantum correlation (HMQC) spectrum with those of a heteronuclear multiple‐bond correlation (HMBC) spectrum is an effective means of detection of coupling to a third nucleus. Two‐dimensional NMR spectroscopy was used to identify the meso form of di‐(trans‐2‐aminocyclohexyl)amine.