Configurational assignments in trifluoromethylvinyl compounds using through-space carbon-fluorine coupling constants

Abstract

Long-range carbon–fluorine coupling constants, nJ(C,F) (n⩾4), were observed for up to six-bond separated nuclei in some substituted trifluoromethylvinyl compounds (CF3CX=CYZ). When the nJ(C,F) in a Z-isomer are compared with those in the corresponding E-isomer, the nJ(C,F) in one isomer whose substituent including the coupled carbon is proximate to the trifluoromethyl group are always larger than those in the other isomer. Because the coupling constants are transmitted through space, the nJ(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 stereoisomers even in the case where only one isomer is obtained. © 1998 John Wiley & Sons, Ltd.