Geometric isomers, also known as cis-trans isomers or E-Z isomers, are a type of stereoisomerism in which molecules have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of those atoms due to the restricted rotation around a double bond or in a ring structure.
Characteristics of Geometric Isomers:
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Cis-Trans Isomers:
- In cis isomers, similar or identical groups are on the same side of a double bond or ring.
- In trans isomers, similar or identical groups are on opposite sides.
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E-Z Notation:
- For compounds with more complex substituents, the E-Z system is used.
- The "E" (from the German "entgegen") indicates that high-priority groups are located on opposite sides, while "Z" (from "zusammen") indicates that they are on the same side.
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Significance:
- Geometric isomers can have different physical and chemical properties, including boiling points, melting points, solubility, and reactivity. This is especially important in biological systems and pharmaceuticals, where the activity of a compound can be highly dependent on its isomeric form.
Example:
A common example is 2-butene:
- Cis-2-butene: The two methyl (–CH₃) groups are on the same side of the double bond.
- Trans-2-butene: The two methyl groups are on opposite sides of the double bond.
Understanding geometric isomerism is crucial in organic chemistry and biochemistry, as it impacts the behavior of molecules in various environments.