Physical Properties of Ethers: Definition, Properties, Uses

You have landed on the right page to learn about the Physical Properties of Ethers. Ethers are a class of organic compounds in which two alkyl groups are attached to both the ends of an \({\text{s}}{{\text{p}}^3}\) hybridised oxygen atom. These are similar to the structure of alcohols, in which the hydrogen atom of the hydroxyl group \(\left({ – {\text{OH}}} \right)\) is attached to an alkyl or aryl group.

As alcohols resemble the structure of water molecules, ethers too resemble it. Ethers have the formula \({\text{R}} -{\text{O}} – {\text{R}}’.\) These compounds are used in perfumes, dyes, oils, waxes and other domestic and industrial purposes. In this article, let’s learn everything about ethers physical properties in detail. Continue reading to know more.

Aliphatic & Aromatic Ethers

In aliphatic ethers, there are no aryl groups directly attached to the ether oxygen atom. For example-

In aromatic ethers, at least one aryl ring is directly attached to the ether oxygen atom. In aryl ethers, the lone pair of electrons on the oxygen atom is in conjugation with the aromatic ring that contributes to the properties of the ether. 

The geometry of ethers is similar to that of alcohols and water. This is due to the presence of an \({\text{s}}{{\text{p}}^3}\) hybridised oxygen atom. The \({\text{R}} -{\text{O}} – {\text{R}}’\) bond angle is close to what is expected in a tetrahedral geometry.

However, the bond angle deviates from the tetrahedral geometry due to the steric repulsion of the alkyl or aryl groups. For example – The bond angle of dimethyl ether is \({111.7^ \circ },\) which is larger than the \({\text{H-O-H}}\) bond angle in water \(\left({{{104.5}^ \circ }} \right)\) due to the steric repulsion of the methyl groups.

Physical Properties of Ethers

The physical properties of ethers are explained below:

Study Uses of Ethers

Physical State

Methoxy methane and methoxy ethane are gases, while other members are volatile liquids with a pleasant smell. Other lower homologues are colourless, pleasant smelling, volatile liquids with typical ether smell.

Polar Nature of Ether

Ethers are polar in nature. This is because there lies an electronegativity difference between the oxygen atom and carbon atom. The electronegativity difference causes the shared pair of electrons to be pulled more by the oxygen atom towards itself, resulting in a partial negative charge over the oxygen atom and a partial positive charge over the carbon atom.

There are two polar \({\text{C}} – {\text{O}}\) bonds in the ether that are inclined to each other at an angle of \({111.7^ \circ }.\) Hence, the two dipoles do not nullify each other, resulting in a net dipole moment.i.e., The dipole moment \(\left( {\rm{\mu }} \right)\) in ether \( \ne 0.\)

Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structures.

The bond angle of ether is due to the \({\text{s}}{{\text{p}}^3}\) hybridisation of the oxygen atom. Even if they are symmetrical, ethers possess a net dipole moment. The dipole moment of dimethyl ether is \(1.3\,{\text{D}}\) and the dipole moment of diethyl ether is \(1.18\,{\text{D}}.\)

The bond angle in ethers is more than that of water. This is because of greater repulsive interaction between bulkier alkyl groups as compared to smaller \({\text{H}}\)-atoms in water.

Hydrogen Bonding of Ether

There is no hydrogen atom directly attached (bonded) to the oxygen atom in ethers. Hence, ethers do not show any intermolecular hydrogen bonding.

However, ethers act as hydrogen bond acceptors only. Hydrogen bonding with water molecules is feasible because oxygen atoms have two lone pairs of electrons.

When compared to linear aliphatic ethers, cyclic ethers such as tetrahydrofuran and \(1,4\)-dioxane are miscible in water due to the more exposed oxygen atom for hydrogen bonding.

Boiling Point of Ether

As ethers do not form intramolecular hydrogen bonds, the boiling point of ethers is lower than that of isomeric alcohols but closer to alkanes having comparable mass. For example, the boiling point of methoxy methane \(\left({{\text{C}}{{\text{H}}_3}{\text{OC}}{{\text{H}}_3}} \right)\) is lower than that of ethanol \(\left({{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}}} \right)\) even though both have the same molecular formula \({{\text{C}}_2}{{\text{H}}_6}{\text{O}}.\)

Solubility of Ether

Ethers, up to three carbon atoms, are miscible in water. This is because lower ethers can readily form a hydrogen bond with water molecules. Ethers comprise the hydrophilic oxygen end, which is polar in nature and the hydrophobic hydrocarbon chain, which is non-polar in nature.

The solubility of ether in water decreases with the size of alkyl groups.

This is because the hydrocarbon part, which is non-polar in nature, resists the formation of hydrogen bonds with the polar water molecules.

Organic solvents such as alcohols, benzene, and acetone are relatively soluble in ethers. 

Example: Diethyl ether and n-butyl alcohol have approximately the same solubility in water. This is because ether forms a hydrogen bond with water much in the same way alcohol does with water.

Acidity

Oxygen bonds are similar in ethers, alcohols, and water. Because oxygen is more electronegative than carbon, the hydrogens alpha to ethers in simple hydrocarbons are more acidic. They are significantly less acidic than alpha to carbonyl groups of hydrogen (such as in ketones or aldehydes).

Density of Ether

Ethers are lighter than water.

Comparisons of Physical Properties of Alcohols and Ethers

Unlike alcohols, ethers have no hydrogen atom attached to the oxygen atom (no \({\text{-OH}}\) group). Due to this reason, ethers act only as hydrogen bond acceptors with no intermolecular hydrogen bonding between ether molecules. This makes their boiling points much lower than their corresponding alcohol with a similar mass. Despite a small dipole moment, ethers have boiling points similar to alkanes of comparable molar mass.

Ether molecules, however, engage in hydrogen bonding with water molecules. Consequently, an ether has about the same solubility in water as the alcohol that is isomeric with it. For example -Diethyl ether and n-butyl alcohol have approximately the same solubility in water. This is because ether forms a hydrogen bond with water much in the same way alcohol does with water.

Summary

Ethers are functional isomers of alcohol. They resemble the structure of alcohol as well as water. Hence, we must learn the basic properties that make it functional isomers of alcohol. In this article, we learnt some of the physical properties of ethers pertaining to their structure.

FAQs

Q.1. Which is more soluble in water, alcohol or ether?
Ans: The \({\text{-OH}}\) group in alcohol acts as hydrogen bond donor and acceptor; however, ethers act only as hydrogen bond acceptor. Hence, alcohol can form more energetically favorable interactions with the solvent than the ether and is more soluble in water than alcohol.

Q.2. Why are ethers soluble in water like alcohol?
Ans: Ethers have two alkyl groups \(\left({{\text{R}} – {\text{O}} – {\text{R}}’} \right)\) attached to the ends of an oxygen atom. Due to the high electronegativity of an oxygen atom, it acts as a hydrogen-bond acceptor and is soluble in water similar to that of alcohols.

Q.3. How do you convert alcohol into the ether?
Ans: The acid catalysed dehydration of primary alcohols leads to the formation of ethers. This kind of reaction is called a condensation reaction, in which two molecules of primary alcohol combine to form a larger one while liberating a small molecule of water.

Q.4. How can you tell the difference between ether and alcohol?
Ans: Ether and alcohols are similar in structure and resemble the structure of water. When an alkyl group replaces one hydrogen atom of a water molecule, alcohol is formed, whereas, in an ether, both hydrogen atoms are replaced by alkyl or aryl groups.

Q5. Are ethers polar or non-polar?
Ans: Ethers are slightly polar. This is because there exists an electronegativity difference between the oxygen and carbon atoms of an ether.

Study Structure of Ethers Here

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