Spectroscopic separation of super(13)C NMR spectra of complex isomeric mixtures by the CSSF-TOCSY-INEPT experiment

Isomeric mixtures from synthetic or natural origins can pose fundamental challenges for their chromatographic separation and spectroscopic identification. A novel 1D selective NMR experiment, chemical shift selective filter (CSSF)-TOCSY-INEPT, is presented that allows the extraction of super(13)C NMR subspectra of discrete isomers in complex mixtures without physical separation. This is achieved via CSS excitation of proton signals in the super(1)H NMR mixture spectrum, propagation of the selectivity by polarization transfer within coupled super(1)H spins, and subsequent relaying of the magnetization from super(1)H to super(13)C by direct INEPT transfer to generate super(13)C NMR subspectra. Simple consolidation of the subspectra yields super(13)C NMR spectra for individual isomers. Alternatively, CSSF-INEPT with heteronuclear long-range transfer can correlate the isolated networks of coupled spins and therefore facilitate the reconstruction of the super(13)C NMR spectra for isomers containing multiple spin systems. A proof-of-principle validation of the CSSF-TOCSY-INEPT experiment is demonstrated on three mixtures with different spectral and structural complexities. The results show that CSSF-TOCSY-INEPT is a versatile, powerful tool for deconvoluting isomeric mixtures within the NMR tube with unprecedented resolution and offers unique, unambiguous spectral information for structure elucidation. Copyright copyright 2014 John Wiley & Sons, Ltd. A novel 1D selective NMR experiment, CSSF-TOCSY-INEPT, is presented that allows the highly selective extraction of super(13)C NMR subspectra of discrete isomers in complex mixtures without physical separation. A proof-of-principle validation of the method is demonstrated on three isomeric mixtures with different spectral and structural complexities taken from our day-to-day laboratory work.