Use of INDOR in a Four-Spin 19F Spectrum for the Assignment of Lines and Relative Signs of Coupling Constants

The NMR spectra of the mixed erythro and threo isomers of trans-CFClBrCFBrCF=CFCl were obtained. The assignment of lines and the relative signs of the coupling constants were determined by the INDOR 19F–19F double-resonance method, using a systematic procedure suitable for this nonsymmetrical nearly first-order four-spin system. Three of the six coupling constants have signs opposite to the other three. Numerical values of shifts and coupling constants are given, as well as higher-order corrections.