Advanced Topic 746 of 1102 Organic Chemistry
E-Z Notation
A CIP priority-based system for naming alkene geometry.
In-depth explanation of E-Z Notation
E-Z notation is the systematic way to describe the geometry of an alkene when the simple cis and trans labels are ambiguous, which happens when each carbon carries more than one different group. The Cahn-Ingold-Prelog priority rules are applied to the two substituents on each carbon of the double bond, and the higher-priority groups are compared. If the two higher-priority groups lie on the same side of the double bond, the isomer is labelled Z, from the German zusammen, meaning together. If they lie on opposite sides, the isomer is labelled E, from entgegen, meaning opposite.
Going deeper: E-Z Notation
Key ideas: Assign CIP priority to the two groups on each double bond carbon separately. If the two higher-priority groups are on the same side, the alkene is Z (zusammen); if on opposite sides, E (entgegen). Priority is based on atomic number at the first point of difference, exploring outward when tied. Duplicate atoms represent double bonds.
Common mistakes and connections: Students equate Z with cis and E with trans in every case, but that fails when the higher priority groups are not the ones used for the cis-trans comparison. They also compare priorities across the double bond instead of on each carbon. Links to CIP rules, nomenclature and the Wittig reaction.
Visualization of E-Z Notation
For 2-butene, Z (higher-priority groups on the same side) boils at 277 K and E (opposite sides) at 274 K, showing E/Z labels describe real isomers. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The compound (Z)-but-2-ene has its two methyl groups on the same side of the double bond.
Frequently asked questions about E-Z Notation
What is E-Z Notation?
A CIP priority-based system for naming alkene geometry.
Is E-Z Notation a beginner, intermediate or advanced topic?
E-Z Notation is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before E-Z Notation?
Study these earlier topics in Organic Chemistry first: Functional Group Isomerism, Stereoisomerism, Cis-Trans Isomerism.
What comes after E-Z Notation?
The next topics in Organic Chemistry are Chirality and Enantiomers.
Can I practise E-Z Notation with quizzes?
Yes. The interactive lesson includes a self-check question on E-Z Notation, and the Organic Chemistry quiz draws on every topic in this area.
Where E-Z Notation fits in Organic Chemistry
E-Z Notation is topic 18 of 148 in Organic Chemistry.