Title: cis, trans
Long Title: IUPAC Gold Book - <i>cis</i>, <i>trans</i>
DOI: 10.1351/goldbook.C01092
Status: current

Definition
Descriptors which show the relationship between two ligands attached to separate atoms that are connected by a double bond or are contained in a ring. The two ligands are said to be located cis to each other if they lie on the same side of a plane. If they are on opposite sides, their relative position is described as trans. The appropriate reference plane of a double bond is perpendicular to that of the relevant $\ce{\upsigma\!\mbox{-}bonds}$ and passes through the double bond. For a ring (the ring being in a conformation, real or assumed, without re-entrant angles at the two substituted atoms) it is the mean plane of the ring(s). For alkenes the terms cis and trans may be ambiguous and have therefore largely been replaced by the E, Z convention for the nomenclature of organic compounds. If there are more than two entities attached to the ring the use of cis and trans requires the definition of a reference substituent.

Related Terms
- <em>E, Z</em>: https://goldbook.iupac.org//terms/view/E01882
- alkenes: https://goldbook.iupac.org//terms/view/A00224
- conformation: https://goldbook.iupac.org//terms/view/C01258
- ligands: https://goldbook.iupac.org//terms/view/L03518

Sources
- Blue Book Guide, p. 149 (https://doi.org/10.1351/pac199971071327)
- PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2203 (https://doi.org/10.1351/pac199668122193)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C01092/html
- json: https://goldbook.iupac.org/terms/view/C01092/json
- xml: https://goldbook.iupac.org/terms/view/C01092/xml

Citation: Citation: '<i>cis</i>, <i>trans</i>' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C01092
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Accessed: 2026-05-31T06:34:13+00:00