Cis–trans isomerism
Geometric isomerism describes cis and trans arrangements of atoms.
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The terms "cis" and "trans" originate from Latin, with "cis" meaning "this side of" and "trans" meaning "the other side of", and in chemistry they indicate whether functional groups lie on the same side or opposing sides of a reference plane.[1]
Quick Facts
- Field
- Chemistry
- Type
- Stereoisomerism
- Related notation
- E–Z notation for alkenes with multiple different substituents
Facts from the source article.
Key facts and history
Cis–trans stereoisomers very often contain double bonds or ring structures, where bond rotation is restricted or prevented.[2] In the cis isomer, the two polar C–Cl bond dipole moments combine to give an overall molecular dipole, raising the boiling point.[3] A diastereomer is called cis when its substituent groups point in the same direction and trans when they point in opposite directions.[2] For pent-2-ene, the cis isomer boils at 37 °C and the trans isomer at 36 °C, showing that boiling-point differences between cis and trans isomers can be quite small.[3]
In acyclic systems, trans isomers are usually more stable than cis isomers because the cis arrangement creates unfavorable steric interactions between substituents.[4]
What the research sources say
A crossed double-bond has been used sometimes but is no longer considered an acceptable style for general use by IUPAC.[5][6] According to Williams' "Spectroscopic Methods in Organic Chemistry", NMR spectroscopy shows that vicinal coupling constants for trans isomers (12–18 Hz, typically 15 Hz) are larger than those for cis isomers (0–12 Hz, typically 8 Hz).[7][8]
References
- Wikipedia, "Cis–trans isomerism" (CC BY-SA 4.0), which cites: Charlton T. Lewis, Charles Short, A Latin Dictionary (Clarendon Press, 1879) Entry for cis (original not read by us) en.wikipedia.org
- Wikipedia, "Cis–trans isomerism" (CC BY-SA 4.0), which cites: Reusch, "Stereoisomers Part I", Virtual Textbook of Organic Chemistry, 2010 (original not read by us) en.wikipedia.org
- Wikipedia, "Cis–trans isomerism" (CC BY-SA 4.0), which cites: "CRC Handbook of Chemistry and Physics", 1979–1980, p. C-298 (original not read by us) en.wikipedia.org
- Wikipedia, "Cis–trans isomerism" (CC BY-SA 4.0), which cites: March, "Advanced Organic Chemistry, Reactions, Mechanisms and structure", 1985, p. 111 (we also read that source) en.wikipedia.org
- Wikipedia, "Cis–trans isomerism" (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
- Wikipedia, "Cis–trans isomerism" (CC BY-SA 4.0), which cites: Williams, "Spectroscopic Methods in Organic Chemistry", McGraw-Hill, 1989 (we also read that source) en.wikipedia.org
- Open Library record, ISBN 9780077072124 ("Spectroscopic methods in organic chemistry"). CC0 (metadata); book content not read. openlibrary.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Cis–trans isomerism (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: Cis–trans isomerism (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
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