13C{2H} Insensitive Nuclei Enhanced by Polarization Transfer (INEPT): a new NMR strategy for isotopic labeling studies

Analysis of the 13C 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

“…As we will demonstrate below, this apparent complexity originates from three distinct NMR effects: the chiral discrimination in the PBLG phase, the enrichment of the mixture and the 1 H/ 2 H isotope effect observed on 13 C chemical shift of deuterium labelled compounds. To understand the analysis and the following discussion, we have to remember that the NMR resonance frequency, ñ i , of a 13 C nucleus i contains both an isotropic, s iso i , and an anisotropic, Ds i , contribution to the electronic shielding and may be written for a pair of enantiomers as: [1,9,10] …”

“…H}) 1D spectrum of 1 recorded in the PBLG/ CHCl 3 oriented phase at 300 K. Interesting and unexpected questions arise when analysing the 13 C NMR spectrum that exhibits sixteen resonances with various peak intensities. As we will demonstrate below, this apparent complexity originates from three distinct NMR effects: the chiral discrimination in the PBLG phase, the enrichment of the mixture and the 1 H/ 2 H isotope effect observed on 13 C chemical shift of deuterium labelled compounds.…”

“…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.…”

“…[6,7] Due to the chiral environment, no plane of symmetry will be conserved in the orientational probability function in such a way that C s molecules will behave as if it were C 1 , C 2v molecules will behave as if they were C 2 and so on. [6,8] The chiral discrimination mechanism described above was derived from the analysis of proton-decoupled deuterium NMR spectra, [5] but no investigations using 13 C NMR spectroscopy have been made so far. [1] It is the purpose of this Abstract: We examined and discuss the protonand 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.…”

“…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. Keywords: chirality ¥ enantioselectivity ¥ isotope effect ¥ liquid crystals ¥ NMR spectroscopy paper to study the consequences of such symmetry lowering in the 13 C NMR of prochiral molecules and in isotopically chiral analogues.…”