Analytical chemistry

Spectral editing of organic mixtures into pure components using NMR spectroscopy and ultraviscous solvents.

PMID 18052233


A general technique is described that permits the extraction of a complete 1H NMR spectrum for components in organosoluble mixtures. The approach should find a wide range of applications considering that pure component spectra can be generated without the need for physical separation. This technique is especially significant for synthetic organic chemistry and the pharmaceutical industry due to the potential to isolate a product spectrum even in the presence of overlapping starting materials, byproducts, or degradation products. A viscous oil-based solvent system that can be temperature-manipulated from essentially a solid at one extreme to a freely flowing liquid at the other is employed. The system contains no protons and is miscible with common organic solvents. Through careful control of the temperature and thus solvent viscosity, the behavior of small molecules moves from the positive to the extreme of the negative NOE regime. Under such conditions, all protons in a molecule correlate with all other protons as propagation by spin diffusion becomes highly efficient, behavior normally only observed with rigid macromolecules in conventional solvents. Therefore, as long as one proton (or carbon signal in hybrid experiments) is resolved for a component in a mixture, the entire proton spectrum for that molecule can be cleanly extracted from a 2D NOESY spectrum (or from selective 1D NOE-based analogues). Preliminary results are highly encouraging, indicating that the approach may be feasible for a wide range of molecules and mixtures; however, in practice the exact types of structures, combinations of structures, and range of concentrations that can be cleanly extracted will become evident as the technique becomes better established.

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Cholesteryl acetate, 97%