Homo- and heteronuclear 2D NMR approaches to analyse a mixture of deuterated unlike/like stereoisomers using weakly ordering chiral liquid crystals

Correlation 2D‐NMR experiments involving both 13C and 2H isotopes in oriented media: methodological developments and analytical applications

“…2 H– 13 C correlation for ordered solutes can be achieved using various schemes, such as 2 H → 13 C HETCOR sequences based on INEPT transfer (Fig. a) as well as 13 C → 2 H → 13 C HSQC and HMQC schemes .…”

“…Additionally, the spectral discrimination of diastereoisomeric forms ( u/l ) in isotropic solutions is not always guaranteed, in particular, when the stereogenic centers are far from each other as in the case of mixtures 1 and 2 (Fig. a) . One possible analytical solution for deuterated solutes consists in using 2 H–{ 1 H} or 13 C–{ 1 H} 1D NMR (deuterated solutes) in CLC that can afford efficient way to separate the signals of three stereoisomers of mixture (the meso compound and the two enantiomers) on the basis of 2 H RQCs or 13 C CSA differences .…”

“…Various multidimensional (nD) NMR experiments have been proposed to facilitate the assignment of anisotropic 2 H signals. These NMR experiments include the following: (i) 2 H autocorrelation two‐dimensional (2D) and three‐dimensional (3D) methods, which correlate the two components of the quadrupolar doublets and permit to assign them on the basis of the 2 H chemical shifts, (ii) 2 H homonuclear correlation 2D experiments via 2 H– 2 H scalar ( n J DD ) and dipolar ( n D DD ) couplings or with 13 C relay, and (iii) 13 C– 2 H correlation 2D experiments, which correlate the 2 H signal with that of the covalently bonded 13 C nucleus and thus allow the assignment of 2 H signals on the basis of 13 C chemical shifts …”

“…Note also that 2 H → 13 C INEPT and DEPT 1D experiments as well as 2 H → 13 C and 13 C → 2 H cross‐polarization (CP) ones using isotropic solvents have been reported in literature . For liquid crystals and solids, 2 H– 13 C correlation experiments have employed either 2 H → 13 C INEPT transfer, 13 C → 2 H → 13 C HMQC scheme, 2 H → 13 C DAPT, or 2 H → 13 C CP transfer . For strongly aligned compounds or solids, the CP transfer is rendered difficult by the intricate spin dynamics of 2 H coherences in the presence of first‐order quadrupolar interaction, which is about 170–210 kHz, and generally exceeds typical rf field strengths .…”

Chemical shift anisotropy edited complete unraveling of overlapped 1H NMR spectra of enantiomers: Application to small chiral molecules

“…Hence the majority of NMR investigations of enantiomeric differentiation have focused on 2 H NMR [5][6][7][8][9][10][11], taking advantage of the relatively large strengths of the quadrupole couplings compared to chemical shift anisotropies and dipolar couplings. The recent study also discusses the use of homo and heteronuclear two-dimensional methods to analyse a mixture of deuterated unlike and like stereo isomers [12]. There are also studies using 13 C [13,14] and 19 F [15,16].…”