E-Z Nomenclature The assignment of geometrical isomers as either E or Z follows on from the Cahn-Ingold-Prelog convention Imagine the double bonds being split into two ends,and assign the priority of the substituents Zusammen Entgegen If the two highest priority groups are on opposite sides of the double bond(trans),the isomer is assigned E. If the two highest priority groups are on the same side of the double bond(cis)the isomer is assigned Z. ①'s together Br CH; ①D Br CH C=C becomes Z CI ② ② (Z)-1-bromo-1-chloropropene Ch07 Alkenes:Struct +synth (landscape) Page 9 Ch07 Alkenes; Struct + synth (landscape) Page 9 E-Z Nomenclature The assignment of geometrical isomers as either E or Z follows on from the Cahn-Ingold-Prelog convention. Imagine the double bonds being split into two ends, and assign the priority of the substituents. If the two highest priority groups are on opposite sides of the double bond (trans), the isomer is assigned E. If the two highest priority groups are on the same side of the double bond (cis) the isomer is assigned Z