Highly Accurate Quantitative Analysis Of Enantiomeric Mixtures from Spatially Frequency Encoded 1H NMR Spectra.

We propose an original concept to measure accurately enantiomeric excesses on proton NMR spectra, which combines high-resolution techniques based on a spatial encoding of the sample, with the use of optically active weakly orienting solvents. We show that it is possible to simulate accurately dipolar edited spectra of enantiomers dissolved in a chiral liquid crystalline phase, and to use these simulations to calibrate integrations that can be measured on experimental data, in order to perform a quantitative chiral analysis. This approach is demonstrated on a chemical intermediate for which optical purity is an essential criterion. We find that there is a very good correlation between the experimental and calculated integration ratios extracted from G-SERF spectra, which paves the way to a general method of determination of enantiomeric excesses based on the observation of 1H nuclei.

Correction: Achieving high resolution and optimizing sensitivity in spatial frequency encoding NMR spectroscopy: from theory to practice.

Correction for 'Achieving high resolution and optimizing sensitivity in spatial frequency encoding NMR spectroscopy: from theory to practice' by Bertrand Plainchont et al., Phys. Chem. Chem. Phys., 2016, 18, 22827-22839.

Achieving high resolution and optimizing sensitivity in spatial frequency encoding NMR spectroscopy: from theory to practice.

A detailed analysis of NMR spectra acquired based on spatial frequency encoding is presented. A theoretical model to simulate gradient encoded pulses is developed in order to describe the spatial properties of the NMR signals that are locally created throughout the sample. The key features that affect the efficiency of the slice selection process during excitation as well as refocusing pulses are investigated on a model ABX spin system, both theoretically and experimentally. It is shown that the sensitivity and resolution of the pure shift and J-edited experiments based on a spatial frequency encoding can be optimized to a point where high-resolution techniques based on a spatial frequency encoding approach show optimal performance compared to other methods.

Fully resolved NMR correlation spectroscopy.

A new correlation experiment cited as "push-G-SERF" is reported. In the resulting phased 2D spectrum, the chemical shift information is selected along the direct dimension, whereas scalar couplings involving a selected proton nucleus are edited in the indirect domain. The robustness of this pulse sequence is demonstrated on compounds with increasing structural and spectral complexity, using state-of-the-art spectrometers. It allows for full resolution of both dimensions of the spectrum, yielding a straightforward assignment and measurement of the coupling network around a given proton in the molecule. This experiment is intended for chemists who want to address efficiently the structural analysis of molecules with an overcrowded spectrum.

Pushing the limits of signal resolution to make coupling measurement easier.

Probing scalar couplings are essential for structural elucidation in molecular (bio)chemistry. While the measurement of JHH couplings is facilitated by SERF experiments, overcrowded signals represent a significant limitation. Here, a new band selective pure shift SERF allows access to δ(1)H and JHH with an ultrahigh spectral resolution.

Combining J-edited and correlation spectroscopies within a multi-dimensional spatial frequency encoding: toward fully resolved 1H†NMR spectra.

J-resolved at a glance: Passive coupling refocusing-COSY experiments based on a frequency encoding of the sample along two directions of space are presented. It allows various spin evolutions to be triggered in different parts of the sample in a selective and fully controlled manner. This yields 2D spectra in which the whole proton network appears as a series of fully resolved and straightforwardly assignable doublets, triplets or quartets (see figure).