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Spin state selective coherence transfer: A method for discrimination and complete analyses of the overlapped and unresolved $^1H$ NMR spectra of enantiomers

Baishya, Bikash and Prabhu, Uday R and Suryaprakash, N (2008) Spin state selective coherence transfer: A method for discrimination and complete analyses of the overlapped and unresolved $^1H$ NMR spectra of enantiomers. In: Journal of Magnetic Resonance . (In Press)

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Abstract

In general, the proton NMR spectra of chiral molecules aligned in the chiral liquid crystalline media are broad and featureless. The analyses of such intricate NMR spectra and their routine use for spectral discrimination of R and S optical enantiomers are hindered. A method is developed in the present study which involves spin state selective two dimensional correlation of higher quantum coherence to its single quantum coherence of a chemically isolated group of coupled protons. This enables the spin state selective detection of proton single quantum transitions based on the spin states of the passive nuclei. The technique provides the relative signs and magnitudes of the couplings by overcoming the problems of enantiomer discrimination, spectral complexity and poor resolution, permitting the complete analyses of the otherwise broad and featureless spectra. A non-selective $180^0$ pulse in the middle of MQ dimension retains all the remote passive couplings. This accompanied by spin selective MQ–SQ conversion leads to spin state selective coherence transfer. The removal of field inhomogeneity contributes to dramatically enhanced resolution. The difference in the cumulative additive values of chemical shift anisotropies and the passive couplings, between the enantiomers, achieved by detecting Nth quantum coherence of N magnetically equivalent spins provides enhanced separation of enantiomer peaks. The developed methodology has been demonstrated on four different chiral molecules with varied number of interacting spins, each having a chiral centre.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier. Online published version available. Other publication details awaited.
Keywords: Spin state selection;Triple quantum;Multiple quantum;Chiral discrimination;PBLG;Product operator;Spectral analyses
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 27 Mar 2008
Last Modified: 19 Sep 2010 04:43
URI: http://eprints.iisc.ernet.in/id/eprint/13522

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