15-crown-5

Definition

15-crown-5 is a type of cyclic polyether compound, also known as a crown ether, that is characterized by a 15-membered ring structure with 5 oxygen atoms evenly spaced around the ring. These crown ethers have a unique ability to selectively bind and transport certain metal cations.

5 Must Know Facts For Your Next Test

1. The 15-membered ring of 15-crown-5 provides a cavity size that is well-suited for binding alkali metal cations, such as sodium (Na+) and potassium (K+).
2. The five oxygen atoms in the 15-crown-5 ring act as electron-rich donor sites, allowing them to coordinate with the positively charged metal cations.
3. The flexibility of the 15-crown-5 structure allows it to adopt a conformation that optimizes the fit and interactions with the bound cation.
4. 15-Crown-5 is commonly used in phase-transfer catalysis, where it facilitates the transfer of ionic species between immiscible phases, such as organic and aqueous solvents.
5. The ability of 15-crown-5 to selectively bind and transport specific cations has applications in areas like ion separation, ion-exchange resins, and electrochemical sensors.

Review Questions

• Explain the structural features of 15-crown-5 that enable it to bind and transport metal cations.
  • The 15-membered ring structure of 15-crown-5 provides a cavity size that is well-suited for accommodating alkali metal cations, such as sodium (Na+) and potassium (K+). The five evenly spaced oxygen atoms within the ring act as electron-rich donor sites, allowing them to coordinate with the positively charged metal cations. The flexibility of the 15-crown-5 structure enables it to adopt a conformation that optimizes the fit and interactions with the bound cation, further enhancing the stability of the complex.
• Describe the applications of 15-crown-5 in various fields, and explain how its cation-binding properties contribute to these applications.
  • The ability of 15-crown-5 to selectively bind and transport specific cations has led to its use in various applications. In phase-transfer catalysis, 15-crown-5 facilitates the transfer of ionic species between immiscible phases, such as organic and aqueous solvents, by forming stable complexes with the target cations. Additionally, the cation-binding properties of 15-crown-5 have been exploited in ion separation techniques, ion-exchange resins, and electrochemical sensors, where the selective complexation with specific cations is crucial for the desired functionality.
• Analyze the role of cation-π interactions in the stability of 15-crown-5-cation complexes, and discuss how this interaction contributes to the overall binding affinity.
  • The stability of 15-crown-5-cation complexes is not only due to the coordination between the oxygen atoms and the metal cation but also involves cation-π interactions. The positively charged cation can interact with the π-electron system of the aromatic ring within the 15-crown-5 structure, resulting in an attractive force that further stabilizes the complex. This cation-π interaction, in addition to the coordination between the oxygen atoms and the cation, enhances the overall binding affinity and contributes to the selective complexation of 15-crown-5 with specific metal cations, such as sodium and potassium.

Related terms

Crown Ether: A class of cyclic polyether compounds that are capable of forming stable complexes with metal cations, with the oxygen atoms providing binding sites for the cation.

Macrocyclic Ligand: A large cyclic molecule that can act as a ligand, forming coordination complexes with metal ions, with the cyclic structure providing a cavity that can accommodate the metal ion.

Cation-π Interaction: An attractive interaction between a positively charged cation and the π-electron system of an aromatic ring, which can contribute to the stability of crown ether-cation complexes.