E/z selectivity

Definition

e/z selectivity refers to the preference for the formation of one stereoisomer over another in chemical reactions involving alkenes, specifically regarding their geometric configuration. The terms 'e' (from the German 'entgegen') and 'z' (from the German 'zusammen') indicate the relative positioning of substituents across a double bond. This selectivity is crucial in understanding the outcome of olefin metathesis, where the desired product often depends on whether an e or z configuration is achieved.

5 Must Know Facts For Your Next Test

1. In e/z selectivity, 'e' configuration has higher priority substituents on opposite sides of the double bond, while 'z' has them on the same side.
2. The selectivity is influenced by sterics and electronic effects, which can affect the stability and reactivity of the intermediates formed during olefin metathesis.
3. Achieving a specific e or z configuration can greatly impact the physical and chemical properties of the resulting compound, including its boiling point and reactivity.
4. Catalysts used in olefin metathesis can favor either e or z products depending on their structure and mechanism, leading to controlled selectivity.
5. In synthetic applications, e/z selectivity is often manipulated to achieve desired outcomes in complex organic molecules.

Review Questions

• How does e/z selectivity influence the outcome of reactions involving alkenes?
  • e/z selectivity significantly influences reaction outcomes by determining which stereoisomer is preferentially formed. The configuration (e or z) affects not only the stereochemical identity of the product but also its physical properties and reactivity. Understanding this selectivity helps chemists design reactions that yield desired products, particularly in processes like olefin metathesis where controlling stereochemistry is critical.
• Discuss how steric and electronic factors contribute to e/z selectivity in olefin metathesis reactions.
  • Steric factors play a crucial role in determining e/z selectivity by influencing the spatial arrangement of substituents around the double bond. Bulky groups may favor an e configuration due to reduced steric hindrance when they are positioned opposite each other. Electronic factors, such as resonance and electronegativity differences among substituents, can also stabilize specific intermediates leading to preferential formation of one stereoisomer over another. These factors together guide the choice of catalyst and reaction conditions to achieve targeted selectivity.
• Evaluate the importance of manipulating e/z selectivity in synthetic organic chemistry and provide examples of its applications.
  • Manipulating e/z selectivity is essential in synthetic organic chemistry because it allows chemists to tailor molecular properties for specific applications. For example, in pharmaceuticals, achieving a particular stereoisomer can be crucial for biological activity; thus, controlling e/z selectivity can lead to more effective drugs. Additionally, e/z selectivity plays a role in materials science where different configurations can result in materials with varying thermal or mechanical properties. By leveraging catalysts and reaction conditions, chemists can strategically produce desired e or z configurations to optimize performance in various applications.

Related terms

Stereoisomers: Compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms.

Alkene: A hydrocarbon that contains at least one carbon-carbon double bond, which is a key feature in reactions like olefin metathesis.

Metathesis: A chemical reaction where two compounds exchange parts to form new compounds, particularly significant in the context of alkene transformations.