E–Z notation

Common card · No. 456860

E–Z configuration, or the E–Z convention, is the IUPAC's preferred method of describing the absolute stereochemistry of double bonds in organic chemistry. It is an extension of cis–trans isomer notation (which only describes relative stereochemistry) that can be used to describe double bonds having two, three or four substituents. E–Z notation can only be used when neither atom of the double bond has two identical atoms or substituent groups attached to it. Following the Cahn–Ingold–Prelog priority rules (CIP rules), each substituent on a double bond is assigned a priority, then positions of the higher of the two substituents on each carbon are compared to each other. If the two groups of higher priority are on opposite sides of the double bond (trans to each other), the bond is assigned the configuration E (from entgegen, German: [ɛntˈɡeːɡən], the German word for "opposite"). If the two groups of higher priority are on the same side of the double bond (cis to each other), the bond is assigned...

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