E/Z-Configuration Exercises

The terms "cis" and "trans" were used historically to describe the stereochemistry of 1,2-disubstituted alkenes but are reserved for the stereochemistry of ring substituents. But what about the naming of tri- and tetra-substituted double bonds? The Cahn-Ingold-Prelog (CIP) method for R/S configuration may be applied. The priority (by at. no.) of the two substituents on both of the sp² carbons of the double bond is determined. If the higher priority (higher at. no.) atoms are "trans", the double bond geometry is "E" (Ger. entgegen, opposite); if "cis", "Z" (Ger. zusammen, together).

Select a compound from the black panel. It will appear in the white panel. Determine the E/Z-geometry of the double bonds. Click the "show E/Z" button to check your answer and display any comments (Notes:). Atom Colors: carbon, gray; hydrogen, light blue; bromine, magenta; chlorine, green; nitrogen, blue; oxygen, red; lithium, pink; silicon, tan; sulfur, yellow. [Notice: Atom numbers (hovering) may not agree with nomenclature numbers. The double bonds in some substituted benzenoid rings will have different E/Z designations depending upon which canonical resonance structure is shown. These designations have no meaning in delocalized structures. See the two vanillins.]