Spectroscopic separation of 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 13 C NMR subspectra of discrete isomers in complex mixtures without physical separation. This is achieved via CSS excitation of proton signals in the 1 H NMR mixture spectrum, propagation of the selectivity by polarization transfer within coupled 1 H spins, and subsequent relaying of the magnetization from 1 H to 13 C by direct INEPT transfer to generate 13 C NMR subspectra. Simple consolidation of the subspectra yields 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 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 © 2014 John Wiley & Sons, Ltd.