(14)Ethers, Epoxides, and Thioethers Notes

Ethers, Epoxides, and Thioethers

Ethers

• Ethers have the general formula R—O—R', where R and R' can be alkyl or aryl groups.
• Ethers can be symmetrical (R = R') or unsymmetrical (R ≠ R').

Structure and Polarity

• Oxygen in ethers is sp^3 hybridized.
• Ethers have a bent molecular geometry.
• The typical C—O—C bond angle is around 110°, close to the tetrahedral angle.
• Ethers have polar C—O bonds due to the electronegativity difference between carbon and oxygen.

Physical Properties of Ethers

• Ethers cannot hydrogen bond with each other, resulting in lower boiling points compared to alcohols of similar molecular weight.
• Ethers can act as hydrogen bond acceptors, forming hydrogen bonds with water and alcohol molecules.
• Ethers are useful solvents because they dissolve both polar and nonpolar substances and are generally unreactive towards strong bases.

Table 14-1. Comparison of the Boiling Points of Ethers, Alkanes, and Alcohols of Similar Molecular Weights

• Alcohols exhibit hydrogen bonding, leading to significantly higher boiling points.
• Ethers have boiling points similar to alkanes with comparable molecular weights.

Table 14-2. Physical Properties of Ether

Solvation of Ions with Ether

• Ionic substances like lithium iodide (LiI) can dissolve in ethers because the ether's lone pairs strongly solvate the small lithium cation (Li^+).
• Ethers are poor at solvating small anions because they cannot act as hydrogen bond donors.

Ether Complexes

• Grignard reagents: Ethers stabilize Grignard reagents by complexing with the magnesium ion, helping to keep the reagent in solution.
• Electrophiles: The nonbonding electrons of ethers can stabilize electrophiles like borane (BH_3).

Crown Ether Complexes

• Crown ethers can complex with metal cations in the center of their ring structure.
• The size of the crown ether ring determines its selectivity for different cation sizes.
• Complexation with crown ethers can enable polar inorganic salts to dissolve in nonpolar organic solvents.

Nomenclature of Ethers

• Common Names: Name the two alkyl groups attached to the oxygen atom, listing them in alphabetical order, and add the word