Properties of Ether

PROPERTIES OF ETHERS

Dipole nature of ether

Ethers have a tetrahedral geometry i.e. oxygen is sp³ hybridized. The C$-$O$-$C bond angle in ether is 110º. Because of the greater electronegativity of oxygen than carbon, the C$-$O bonds are slightly polar and are inclined to each other at an angle of 110஬, resulting in a net dipole moment.

The bond angle is slightly greater than the tetrahedral angle due to repulsive interaction between the two bulky groups.

Chemical Reaction

Dialkyl ethers reacts with very few reagents other than acids. The only active site for other reagents are the C$-$H bonds of the alkyls. Ethers has ability to solvate cations (electrophile) by donating an electron pair from their oxygen atom. These properties make ether as solvents for many reactions.

On standing in contact with air, most aliphatic ethers are converted slowly into unstable peroxides.

Ether gives following reactions:

1.  Nucleophilic substitution reactions

Note:

Type of ethers also make a difference in the mechanism followed during the cleavage of C$-$O by HI/HBr.

Methyl cation is stabler than phenyl cations

(B) Dehydration with H₂SO₄/$\Delta$ and Anhy Al₂O₃/$\Delta$

     (i)   When both alkyl groups has $\beta$ - hydrogen.

(ii) When only alkyl group has $\beta$ - hydrogen. 

$\bullet$ Hot਌onc. H₂SO₄ react with secondary and tertiary ethers to give a mixture of alcohols and alkenes.

(c)    Miscellaneous reactions

     (1) Halogenation:

           Monohalogenation takes place at $\alpha$  ꃊrbon (with small amount) 

(2) Reaction with CO: give ester

          $R-O-R+CO\underset{200atm,B{F}_3}{\overset{125-{180}^{0}C}{\to }}RCOOR$

Illustration 1. Explain why sometimes explosion occurs while distilling ethers.

Solution:        It is due to formation of peroxide

Illustration 2. The basicity of the ethers towards BF₃ has the following order, explain.

Solution:                   There are steric effects in the Lewis acid-Lewis base complex formation between BF₃ and the respective ethers.