Nuclear Magnetoelectric Shieldings for Chiral Discrimination in NMR Spectroscopy. Theoretical Study of (Ra)-1,3-Dimethylallene, (2R)-2-Methyloxirane, and (2R)-N-Methyloxaziridine Molecules.

Dynamic magnetoelectric shieldings at the nuclei, having the same magnitude but opposite sign in d and l enantiomers, have been evaluated at the random-phase approximation level of accuracy for three chiral molecules of medium size. For frequencies normally operated in nuclear magnetic resonance spectroscopy, calculated values are probably too small to be detectable in disordered phase. Within the same experimental conditions, the isotropic part of nuclear magnetic shielding polarizability and a related pseudoscalar provide contributions 3 orders of magnitude bigger than the average magnetoelectric shieldings to (i) the magnetic field induced at a resonant nucleus and (ii) the induced electric dipole of electrons rotating at the Larmor frequency; therefore, nuclear magnetic shielding polarizabilities are probably more suitable than nuclear magnetoelectric shieldings for chiral discrimination in nuclear magnetic resonance spectroscopy.