Friday, May 19, 2006

Chemical Physics: Detection of Chirality via Solution NMR.

Comment: Detection of chirality via solution NMR. Could have many applications.

Chemical Physics
Vol: 324 Issue: 1, May 9, 2006
pp: 111-116

Direct chiral discrimination in NMR spectroscopy
A.D. Buckingham
a, , P. Fischer b, a Department of Chemistry, Cambridge University, Cambridge CB2 1EW, UKb The Rowland Institute at Harvard, Harvard University, Cambridge, MA 02142, USAReceived 30 June 2005; accepted 6 October 2005

Conventional nuclear magnetic resonance spectroscopy is unable to distinguish between the two mirror-image forms (enantiomers) of a chiral molecule. This is because the NMR spectrum is determined by the chemical shifts and spin–spin coupling constants which – in the absence of a chiral solvent – are identical for the two enantiomers. We discuss how chirality may nevertheless be directly detected in liquid-state NMR spectroscopy: In a chiral molecule, the rotating nuclear magnetic moment induces an electric dipole moment in the direction perpendicular to itself and to the permanent magnetic field of the spectrometer. We present computations of the precessing electric polarization following a π/2 pulse. Our estimates indicate that the electric polarization should be detectable in favourable cases. We also predict that application of an electrostatic field induces a chirally sensitive magnetization oscillating in the direction of the permanent magnetic field. We show that the electric-field-perturbed chemical shift tensor, the nuclear magnetic shielding polarizability, underlies these chiral NMR effects.

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