C

Cis-Trans Isomerism

Quick Reference
Also Known AsGeometric isomerism, E/Z isomerism, cis-trans stereoisomerism

What is Cis-Trans Isomerism?

Cis-trans isomerism (geometric isomerism) occurs when atoms or groups cannot rotate freely due to a double bond or ring structure, resulting in compounds with the same molecular formula but different spatial arrangements. Cis isomers have like groups on the same side; trans isomers have them on opposite sides. These isomers have different physical and sometimes chemical properties.

Properties & Characteristics

Cis-trans isomerism (geometric isomerism) is a form of stereoisomerism where molecules have the same molecular formula and bond connectivity but differ in the spatial arrangement of substituents around a bond with restricted rotation (C=C double bond) or a ring. The E/Z designation uses Cahn-Ingold-Prelog rules to assign priority. Interconversion requires breaking and reforming the double bond.

Uses & Applications

Cis-trans isomerism is important in biochemistry (retinal Z→E photoisomerisation drives vision), drug design (cisplatin vs. transplatin), polymer chemistry (cis-1,4-polyisoprene = natural rubber; trans-1,4-polyisoprene = gutta-percha), and flavour chemistry.

Safety Information

Distinct cis and trans isomers can differ dramatically in toxicity, bioactivity, and environmental persistence. The wrong isomer in a pharmaceutical can be inactive or toxic. Rigorous stereochemical characterisation (NMR, X-ray) is required in drug development.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Cis-Trans Isomerism
Synonyms Geometric isomerism, E/Z isomerism, cis-trans stereoisomerism

Frequently Asked Questions

Cis-trans isomerism (geometric isomerism) occurs when atoms or groups cannot rotate freely due to a double bond or ring structure, resulting in compounds with the same molecular formula but different spatial arrangements. Cis isomers have like groups on the same side; trans isomers have them on opposite sides. These isomers have different physical and sometimes chemical properties.

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