2D 19F/19F NOESY for the assignment of NMR spectra of fluorochemicals

Two-dimensional (2D) NMR is an invaluable technique for the complete analysis and assignment of chemical structures. Although F-19/F-19 COSY experiments are routinely used for assignments in perfluorochemicals, interpretation can be difficult because four-bond ((4)J(FF)) coupling constants are typically 5-10-fold larger than vicinal ((3)J(FF)) coupling constants. Furthermore, the dependence of long range coupling constants on stereochemistry is not always known. Fluorine-fluorine NOESY correlations represent an enhancement in the arsenal of 2D F-19 NMR experiments. The NOESY and COSY spectra of 2,2,3,3,4,4,4-heptafluorobutanol and a telomeric perfluorochemical iodide show that COSY identifies the 1,4-fluorine interactions whereas NOESY identifies the vicinal fluorine atoms. The combined experiments have been used to unambiguously assign all of the fluorines in a mixture of cis- and trans-perfluoro-1,3-dimethylcyclohexane and in a substituted perfluorotetrahydrofuran. (C) 2004 Elsevier B.V. All rights reserved.