Electric field effects on nuclear spin–spin coupling tensors and chiral discrimination via NMR spectroscopy

Abstract

Nuclear magnetic resonance spectrometers presently available are unable to recognize the two mirrorimage forms of a chiral molecule, because in the absence of a chiral solvent, the NMR spectral parameters (chemical shifts and spin–spin coupling constants) are identical for the two enantiomers. This paper discusses how chirality may nevertheless, at least in theory, be recognized in liquid-state NMR spectroscopy by applying strong d.c. electric fields and measuring a pseudoscalar contribution to nuclear spin–spin coupling polarizability. Calculations are reported for medium-size chiral molecules, (2R)-N-methyloxaziridine, (Ra)-1,3-dimethylallene, and (2R)-2-methyloxirane. The very small contributions provided by the pseudoscalar of nuclear spin–spin coupling polarizability seem rather difficult to detect via NMR experiments in disordered phase.