Physical Properties of Ethers

Ethers are a very interesting class of organic compounds. There are several essential chemical and physical properties of ethers that make them some of the most useful organic compounds. 

Ethers are characterised by the presence of one oxygen atom that is attached to two different alkyl and aryl groups. Generally, the formula for ethers is:

R-O-R, R-O-Ar or Ar-O-Ar (Here, R refers to alkyl groups and Ar refers to aryl groups)

The unique physical properties of ethers allow them to react chemically with several compounds. The physical structure of ethers helps determine their nomenclature, industrial purposes, appearance, odour, and chemical reactivity.

Objectives and functions

Ether molecules do not exhibit hydrogen bonding among themselves. This unique feature sets them apart from alcohol. This causes their boiling points to be essentially low and makes them less soluble in water. Because of this physical property of ethers, we find that they are often used as solvents for chemical reactions and experiments.

Structure of ethers

In ethers, there are C-O-C linkages that are at 104.5 degrees, where the distance between C-O pairs is about 140 picometers. Moreover, the oxygen in ethers is more electronegative than its carbon atoms. Thus, alpha hydrogens are more acidic than other normal hydrocarbon chains.

Classification of ethers

Ethers can be classified into two categories on the basis of differences in their physical structure. The classification depends upon the nature of substituent groups that are attached to the main compound.

• Symmetrical ethers: These ethers have two identical (alkyl or aryl) groups attached to the oxygen atom of the molecule. 

Example: CH3OCH3

• Asymmetrical ethers: These ethers have two different groups attached to the oxygen atom. The hydrolysis of unsymmetrical ethers gives two different products. One of the products will be alcohol.

Example: CH3-O-C2H5

Nomenclature of ethers

There are two unique ways in which ethers can be named. One of the preferred ways of naming ethers is by identifying alkyl groups attached to either side of the oxygen atoms. The alkyl groups are identified and named in alphabetical order, followed by the word ‘ether’. 

For example, ethyl methyl ether is one such way of nomenclature. Here, both ethyl and methyl groups are attached to the oxygen atom of the ether. If the two alkyl groups attached to the oxygen atom are the same, then the compound is named di (alkyl) ether—for example, diethyl ether.

On the other hand, the IUPAC method is also used for the naming of ethers. For this method, a specific order of chemical components has to be kept in mind before the naming process. This consists of a short alkyl chain, oxygen, and a long alkyl chain. 

For example, the IUPAC method of naming ethyl methyl ether will be methoxy ethane. In the case of cyclic ethers, the stem of the compound is always known as a cycloalkane. ‘Oxa’ is used to indicate the replacement of oxygen with carbon in the ring.

For example, oxacyclopentane is an example of a five-membered ring with four carbon atoms and one oxygen atom. 

Physical properties of ethers

• The polarity of the C-O bond in ether is responsible for the net dipole moment in the molecule. 
• The boiling point for ethers is similar to alkanes. The boiling point for ethers is less than alcohols that have the same molecular mass. This is also because of the polarity of the C-O bond in the molecule. 
• Ethers have the same miscibility in water as alcohols.
• Ether is miscible in water because, like alcohols, the oxygen atom in ethers can form hydrogen bonds with water molecules. 
• Ethers have around three available carbon atoms, which makes them soluble in water due to hydrogen bonding.
• The solubility of ethers decreases with the increase in carbon atoms in the molecule. This is because the increase in hydrocarbon composition can decrease the level of hydrogen bonding between molecules.
• Ethers are soluble in organic solvents like benzene, acetone, and alcohol, among others. 

Conclusion

Ethers are organic compounds that are characterised by the presence of two alkyl or aryl groups attached to their oxygen atoms. They are soluble in water and can also create a wide variety of compounds through chemical reactions. They are used with organic solvents for a wide variety of industrial purposes. 

The physical properties of ethers are named through two different nomenclature methods. For one method, the name of the attached alkyl groups is attached alphabetically along with ‘ether’, whereas the other method follows the conventions of the IUPAC system. On the basis of their physical characteristics, ethers can be divided into symmetrical and asymmetrical classes as well.