title: Spectroscopic separation of (13) C NMR spectra of complex isomeric mixtures by the CSSF-TOCSY-INEPT experiment.
abstract: 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.
authors.affiliation: R&D Division, Firmenich SA, Route des Jeunes 1, P.O. Box 239, CH-1211, Geneva 8, Switzerland.
authors.forename: Lu
authors.initials: L
authors.lastname: Yang
authors.forename: Aitor
authors.initials: A
authors.lastname: Moreno
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fieber
authors.forename: Robert
authors.initials: R
authors.lastname: Brauchli
authors.forename: Horst
authors.initials: H
authors.lastname: Sommer
keywords: 13C; 1H; CSSF-TOCSY-INEPT; NMR; analysis of complex mixtures; chemical selective filter