E,Z system

Definition

The E,Z system is a notation used in organic chemistry to describe the stereochemistry of double bonds, indicating the relative positions of substituents around an alkene. It assigns the labels "E" (from the German "Entgegen," meaning opposite) for isomers with high-priority groups on opposite sides of a double bond, and "Z" (from the German "Zusammen," meaning together) when they are on the same side.

Related terms

Stereocenters: A point in a molecule where swapping two groups leads to a different stereoisomer; essential for understanding molecular geometry and reactivity.

Cis: Trans Isomerism - A simpler form of stereochemical notation that describes similar phenomena in smaller alkenes but relies on direct comparison rather than priority rules.

Priority Rules (Cahn: Ingold-Prelog rules) - A set of guidelines used to assign priorities to substituents attached to a stereocenter or double bond in order to determine configurations such as R/S and E/Z