Chemical shift anisotropy edited complete unraveling of overlapped $^1H$ NMR spectra of enantiomers: Application to small chiral molecules

Prabhu, Uday Ramesh and Baishya, Bikash and Suryaprakash, N (2008) Chemical shift anisotropy edited complete unraveling of overlapped $^1H$ NMR spectra of enantiomers: Application to small chiral molecules. In: Journal of Magnetic Resonance, 191 (2). pp. 259-266.

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Abstract

The differential values of NMR spectral parameters like chemical shift anisotropies, dipolar couplings and quadrupolar couplings of enantiomers in chiral liquid crystalline media are employed not only for their visualization but also for their quantification. Large differences in chemical shift anisotropies and the quadrupolar couplings between the enantiomers enable the use of $^{13}C$ and extensive $^2H$ NMR detection for such a purpose. In spite of high magnetic moment, high sensitivity and abundant presence of protons in all the chiral molecules, $^1H$ detection is not routinely employed due to severe overlap of unresolved transitions arising from short and long distance couplings. Furthermore, the doubling of the spectra from two enantiomers and their indistinguishable overlap due to negligible difference in chemical shift anisotropies hampers their discrimination. The present study demonstrates the use of proton chemical shift anisotropy as an exclusive parameter for such a discrimination. The method employs the non-selective excitation of homonuclear Nth quantum coherence of N coupled protons. The simultaneous flipping of all the coupled spins results in a single transition in the multiple quantum dimension at the cumulative sum of their anisotropic chemical shifts for each enantiomer, with the measurable difference between them, resulting in their complete unraveling.

Item Type:	Journal Article
Publication:	Journal of Magnetic Resonance
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	Multiple quantum;Chemical shift anisotropy;Chiral discrimination.
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	03 May 2008
Last Modified:	19 Sep 2010 04:44
URI:	http://eprints.iisc.ac.in/id/eprint/13804

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