Analysis of the ~(13)C NMR Spectra of Molecules,Chiral by Isotopic Substitution,Dissolved in a Chiral Oriented Environment:Towards the Absolute Assignment of the pro-R/pro-S Character of Enantiotopic Ligands in Prochiral Molecules

摘要

We examined and discuss the proton-and deuterium-decoupled carbon-13 1D spectrum of a molecule,chiral by virtue of the isotopic substitution,dissolved in a chiral oriented medium which simultaneously exhibits chiral discrimination,enantiomeric enrichment and isotope effect.Using the l-deutero-(2',3',4',5',6'-pentadeutero-phenyl)phenylmethanol orientationally ordered in a chiral nematic liquid crystal as illustrative example,we point out three important features.First,we demonstrate that the absolute assignment of the pro-R/pro-S character may be derived from the absolute configuration of the isotopically chiral analogue.Second,we report evidence that isotopic effect on ~(13)C chemical shift anisotropy is negligible in a weakly orienting solvent.Third,we definitely establish that the molecular orientation of prochiral C_s symmetry molecules and their parent compounds that are chiral by virtue of the isotopic substitution is the same.