CONFIGURATIONAL ASSIGNMENTS IN TRIFLUOROMETHYLVINYL COMPOUNDS USING THROUGH-SPACE CARBON-FLUORINE COUPLING-CONSTANTS

Long-range carbon-fluorine coupling constants, (n)J(C,F) (n greater th an or equal to 4), were observed for up to six-bond separated nuclei i n some substituted trifluoromethylvinyl compounds (CF3CX=CYZ). When th e (n)J(C,F) in a Z-isomer are compared with those in the corresponding E-isomer, the (n)J(C,F) in one isomer whose substituent including the coupled carbon is proximate to the trifluoromethyl group are always l arger than those in the other isomer. Because the coupling constants a re transmitted through space, the (n)J(C,F) decrease with increase in the spatial distance of the carbon and the fluorine. This relationship can be used to determine the configurational assignments in the two s tereoisomers even in the case where only one isomer is obtained. (C) 1 998 John Wiley & Sons, Ltd.