Structure of Ethers: Naming and Classification

Structure of Ethers: Do you know race car drivers use Methyl-t-butyl ether (MTBE) to increase the speed of their cars? MTBE helps to burn the gasoline more effectively, enhancing more car engine power. But,65 its use is being discontinued due to concerns about contamination of drinking water by leaking fuel tanks that contained this compound.

What does Ether Mean?

Ether is an organic compound in which two hydrocarbon groups (alkyl or aryl) are bonded to the same atom of oxygen. An ether is represented by the general formula \(\rm{R−O−R}’\) as shown below.

The \(\rm{R}’\) in the formula means that the hydrocarbon group can be the same as \(\rm{R}\), or it can be different.

Naming of Ethers

The steps for the naming of ethers are listed below:

1. In the IUPAC system, ethers are named alkoxy substituents (\(—\rm{OR} =\) alkoxy group). The -yl ending of alkyl substituents is replaced by -oxy. For example —\(\rm{CH}_3\) methyl as —\(\rm{O CH}_3\) methoxy, —\(\rm{CH}_2 \rm{CH}_3\) ethyl as —\(\rm{OCH}_2 \rm{CH}_3\) ethoxy.
2. The parent compound is given by the word ether, which appears at the end of the name.
3. The names of each alkyl group comes before the word ether. If the two alkyl groups are the same, the prefix –di is used. If the two alkyl groups are different, they are listed in alphabetical order.
4. Spaces are left between the names of the alkyl groups (if different) and before the word ether.

Shown below are two examples of ethers with their IUPAC names.

Diethyl ether can also be named ethoxy ethane. Methyl propyl ether is also named as \(1-\) Methoxypropane

Structure of Ethers

Ethers are obtained when the hydrogen atom of the hydroxyl group in alcohols is replaced by an alkyl or aryl group. For example-

Hybridisation

Hybridisation of oxygen in \(\rm{C-O-C}\) bond \(=\) number of atoms attached \(+\) Lone pair of electrons
\(= 2 + 2 = 4 → \rm{sp}^3\) hybridized
Hybridisation of carbon in \(\rm{C-O-C}\) bond \(=\) number of atoms attached \(+\) Lone pair of electrons
\(= 4 + 0 = 4 → \rm{sp}^3\) hybridized
Shape: As the carbon and oxygen both exhibit \(\rm{sp}^3\) hybridization, the expected shape of ethers should be tetrahedral with a bond angle of \(109.28\)’. In ethers, due to the repulsion between two lone pairs (lp) on the oxygen atom, the ethers have a bent shape.
Bond angle: The presence of bulky groups at both ends of the oxygen atom creates a steric hindrance. This results in the repulsion between bond pairs (bp) which is more than the \(\rm{lp-lp}\) repulsion. This \(\rm{bp-bp}\) repulsion results in a \(\rm{C–O–C}\) bond angle of about \(111.7°\).
Bond length: The \((\rm{C–O})\) bond distances in ethers is about \(140\,\rm{pm}\). The barrier to rotation about the \(\rm{C–O}\) bonds is low.

Bond polarity: As the \(\rm{C-O-C}\) bond has a bent shape, the \(\rm{C–O}\) bonds dipoles do not cancel out. This makes ethers polar. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structures. The presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible. Cyclic ethers such as tetrahydrofuran and \(1, 4-\) dioxane are miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to linear aliphatic ethers.
Acidity: The bonding of oxygen in ethers, alcohols, and water is similar. Oxygen is more electronegative than carbon; thus, the hydrogens at an alpha position to the oxygen atom of ethers are more acidic than in simple hydrocarbons. They are far less acidic than hydrogens at an alpha position to carbonyl groups (such as in ketones or aldehydes).
Classification: Depending on the groups at \(\rm{R}\) and \(\rm{R′}\), ethers are classified into two types:
1. Simple ethers or symmetrical ethers: In these ethers, the oxygen atom is bonded to the same alkyl groups. For example-

2. Mixed ethers or asymmetrical ethers: In these ethers, the oxygen atom is bonded to two different alkyl groups. For example-

Properties of Ethers

Solubility: Ethers are also quite soluble in water. This is because the lone-pair electrons on the oxygen atom of the ether form a hydrogen bond with the hydrogen atoms of water molecules. The solubility is greater for ethers that have a shorter length of R groups. As the carbon chains become longer, the van der Waals interactions of the extended carbon chain dominate over hydrogen bonding.
Boiling Point: The boiling points of ethers are much lower than the boiling points of their analogous alcohols. Due to the absence of weak intermolecular hydrogen bonding, ethers exhibit boiling points much closer to their corresponding alkanes.

Uses: Ether was used as a general anesthetic for patients undergoing surgery for many years. However, ethers are very flammable and have undesirable side effects such as nausea and vomiting. The primary use of ethers today is as a solvent for other organic compounds.

Structure of Alcohols Phenols and Ethers

Alcohol, phenol, and ether are classes of organic compounds that find wide usage in a broad range of industries and domestic purposes.

1. Alcohol is formed when a saturated carbon atom is bonded to a hydroxyl \((-\rm{OH}\)) group.
2. Phenol is formed when a hydrogen atom in a benzene molecule is replaced by the hydroxyl group \((-\rm{OH}\))
3. Ether is formed when an oxygen atom is connected to two alkyl or aryl groups.

In alcohols, the oxygen of the \(–\rm{OH}\) group is attached to carbon by a sigma \((σ)\) bond formed by the overlap of a \(\rm{sp}^3\) hybridized orbital of carbon with a \(\rm{sp}^3\) hybridized orbital of oxygen. The bond angle in alcohols is slightly less than the tetrahedral angle \((109°28′)\). It is due to the repulsion between the unshared electron pairs of oxygen.

In phenols, the \(–\rm{OH}\) group is attached to \(\rm{sp}^2\) hybridized carbon of an aromatic ring. The carbon-oxygen bond length \((136\,\rm{pm})\) in phenol is slightly less than that in methanol. This is due to-
(i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring, and
(ii) \(\rm{sp}^2\) hybridized state of carbon to which oxygen is attached.
The \(\rm{C-O-H}\) bond angle in phenol is \(109^o\).

In ethers, the four-electron pairs, i.e., the two bond pairs and two lone pairs of electrons on the oxygen atom, are arranged approximately in a tetrahedral arrangement. The \(\rm{C-O-R}\) bond angle in ether is \(111.7^o\) is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky \((–\rm{R})\) groups. The \(\rm{C–O}\) bond length \((141\,\rm{pm})\) is almost the same as in alcohols.

Summary

Ethers are compounds in which the oxygen atom is sandwiched between two identical or different alkyl groups. In this article, we learned the structure, nomenclature, and properties of ether. We also learned the difference an ether has from its analogous alcohols and alkanes.

FAQs on Structure of Ethers

Q.1. Is ether a hydrocarbon?
Ans: Ether is a hydrocarbon represented by the general formula \(\rm{R−O−R’}\). The \(\rm{R’}\) in the formula means that the hydrocarbon group can be the same as \(\rm{R}\), or it can be different.

Q.2. What are the rules for naming ethers?
Ans: The rules for naming ether are:

1. The parent compound of an ether consists of the word ether, which appears at the end of the name.
2. The names of each alkyl group come before the word ether. If the two alkyl groups are the same, the prefix –di is used. If the two alkyl groups are different, they are listed in alphabetical order.
3. Spaces are left between the names of the alkyl groups (if different) and before the word ether.
4. In the IUPAC system, ethers are named alkoxy substituents \((—\rm{OR} =\) alkoxy group). The -yl ending of alkyl substituents is replaced by -oxy. For example \(—\rm{CH}_3\) methyl as \(—\rm{OCH}_3\) methoxy, \(—\rm{CH}_2 \rm{CH}_3\) ethyl as \(—\rm{OCH}_2 \rm{CH}_3\) ethoxy. For example- Diethyl ether – Ethoxy ethane, Ethyl phenyl ether – Ethoxy benzene

Q.3. What are the characteristics of ethers?
Ans: 1. Ethers are quite soluble in water.
2. The boiling points of ethers are much lower than the boiling points of their isomeric alcohols and much closer to their analogous alkanes.
3. Ethers are volatile and flammable.

Q.4. How do you identify ether?
Ans: Feigl’s test: Take \(1 – 2\,\rm{mL}\) of an unknown compound in a boiling tube and cover the mouth of the tube with a filter paper moistened with a mixture of cupric acetate and benzidine hydrochloride solution. Heat the tube to boiling. The appearance of a deep blue colour indicates the presence of ether.
Iodine test: Iodine in carbon disulfide solution gives a purple-coloured layer of ether.

Q.5. What are mixed ethers? Give examples.
Ans: Mixed ethers or asymmetrical ethers: In these ethers, the oxygen atom is bonded to two different alkyl groups. For example-

Q.6. What is the molecular formula of diethyl ether?
Ans: The molecular formula of diethyl ether is ((\rm{C}_2 \rm{H}_5)_2 \rm{O}.)

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