Deuterium NMR stereochemical analysis of threo–erythro isomers bearing remote stereogenic centres in racemic and non-racemic liquid crystalline solvents

2H NMR Studies on Two‐Homopolypeptide Lyotropic Enantiodiscriminating Mesophases: Experimental Quantification of Solute–Fiber Affinities

“…This results in identical average magnetic interactions for the enantiomers, and thus no difference in their 2 H NMR spectra can be observed (see Supporting Information). [10] In this context, it would be pertinent to explore oriented mixtures made by two polypeptides with the same absolute configuration but with substantial chemical differences in their lateral chains. A similar approach was explored for mixtures of two achiral thermotropic liquid crystals.…”

“…So far, mixtures of two polypeptides were only employed to provide achiral mesophases in which any enantiodiscrimination disappears (see Figure SI-1 in the Supporting Information). [4,10] These compensated mixtures, denoted "PBG" and "PCBL", are prepared by mixing equal amounts by weight of polypeptides of the same nature but with opposite absolute configuration, for example, PBLG and its enantiomer PBDG, or PCBLL and PCBDL. [4,10] In these compensated systems, the two enantiomers exchange rapidly, on the NMR timescale, between the vicinities of land d-polypeptides.…”

“…[4,10] These compensated mixtures, denoted "PBG" and "PCBL", are prepared by mixing equal amounts by weight of polypeptides of the same nature but with opposite absolute configuration, for example, PBLG and its enantiomer PBDG, or PCBLL and PCBDL. [4,10] In these compensated systems, the two enantiomers exchange rapidly, on the NMR timescale, between the vicinities of land d-polypeptides. This results in identical average magnetic interactions for the enantiomers, and thus no difference in their 2 H NMR spectra can be observed (see Supporting Information).…”

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

“…This average value of DC(D) aniso corresponds to the value that would be measured in an achiral oriented phase made of a racemic mixture of PBLG and PBDG (the PBLG×s enantiomer). [15] In such a racemic ordered solvent, denoted PBG, a solute is diffusing very rapidly on the NMR time scale from PBLG to PBDG fibres, consequently we observe only an average of these two situations, thus eliminating the spectral enantiodiscrimination. [15] The comparison between and DC(D) average aniso and DC(D) iso shows no differences within the experimental errors.…”

“…[15] In such a racemic ordered solvent, denoted PBG, a solute is diffusing very rapidly on the NMR time scale from PBLG to PBDG fibres, consequently we observe only an average of these two situations, thus eliminating the spectral enantiodiscrimination. [15] The comparison between and DC(D) average aniso and DC(D) iso shows no differences within the experimental errors. Such a result suggests therefore that the contribution of the isotope effect to the anisotropic component, Ds i , of 13 C chemical shift is negligible at least, in a weakly ordering, chiral solvent.…”