Pure Shift 2D and 1D NMR in Tabular Domain via Complete Reduction to Amplitude Frequency Table [CRAFTps]

Pure shift spectra significantly improve the resolution in NMR by collapsing all multiplet signals into singlets. Homonuclear BB decoupling is typically accomplished by selective inversion of passive spins midway between dwell points or chunks of dwell points during acquisition, and the magnetization is sampled when all the multiplet vector trajectories are at or very near their chemical shift trajectory. In the absence of such synchronous inversion, describing the chemical shift vector trajectory narrows down to (i) mathematically describing the FID in a tabular format of its component signals and (ii) sorting the table into subgroups, each describing a set of vectors (i.e., multiplet signals) that precess in unison around their chemical shift. A processing workflow, based on the CRAFT (Complete Reduction to Amplitude Frequency Table) technique, converts the 2D NMR data set into two-dimensional pure shift CRAFT table (CRAFTps). The CRAFTps table is a mathematical (tabular domain) descriptor of the input data in chemical shift terms that can be used to generate pure shift 2D and 1D spectra. The CRAFTps process is generic and applicable to routinely acquired 2D NMR data and requires no special pulse sequence element. Its applicability is demonstrated with examples of data from three major groups of correlation experiments routinely generated and used in organic structure elucidation by NMR. The CRAFTps process generates pure shift spectra that have significantly better sensitivity (S/N) (as much as ∼30× to 40×), resolution, and peak width compared to the FT2d counterpart. The process requires no user guidance and, hence, minimal bias.