E–Z notation
IUPAC method for double-bond stereochemistry using priority rules.
Last updated
E–Z notation describes the spatial arrangement of substituents around a double bond using priority rules.[1] The configuration is E when the two higher-priority groups lie on opposite sides, and Z when they are on the same side.[1] The CIP rules, which assign priorities to each substituent on a double bond, are used to compare the positions of the two higher-priority substituents on each carbon.[1]
Last updated 2026-09-30 from the source article.
Quick Facts
- Field
- Organic chemistry
- Known for
- Describing absolute stereochemistry of double bonds
- Method
- Cahn–Ingold–Prelog priority rules (CIP rules)
- Notation
- E (entgegen, 'opposite') and Z (zusammen, 'together')
Facts from the source article.
Key facts and history
The notation applies the Cahn–Ingold–Prelog priority rules to assign priorities to each substituent on a double bond.[1] If they are on the same side, the bond is designated Z, from the German word zusammen meaning "together".[1] The prefix "E/Z-" can indicate uncertainty about which isomer is present for an ene bond.[2] A crossed double-bond symbol was sometimes used but is no longer considered acceptable by IUPAC for general use.[2]
Computer software may still require the crossed double-bond style despite the IUPAC recommendation.[2] Wavy single bonds are the conventional method in diagrams to indicate stereochemistry that is unknown, unspecified, or a mixture of isomers.[2]
What the research sources say
That same publication states that a crossed double-bond is no longer an acceptable style for general use by IUPAC.[2][3] The 2006 recommendations also note that the crossed double-bond may still be required by computer software.[2][3] According to the 2006 IUPAC Recommendations by Jonathan Brecher, wavy single bonds are used to denote stereochemistry that is unknown, unspecified, or a mixture of isomers.[2][3]
References
- Wikipedia, "E–Z notation" (CC BY-SA 4.0), which cites: "Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013" (original not read by us) en.wikipedia.org
- Wikipedia, "E–Z notation" (CC BY-SA 4.0), which cites: Brecher, "Graphical representation of stereochemical configuration (IUPAC Recommendations 2006)", Pure and Applied Chemistry, 2006, p. 1897–1970 (we also read that source) en.wikipedia.org
- Jonathan Brecher, "Graphical representation of stereochemical configuration (IUPAC Recommendations 2006)", Pure and Applied Chemistry (2006), doi:10.1351/pac200678101897. OpenAlex metadata CC0; paper not read. doi.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article E–Z notation (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: E–Z notation (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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