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Ethers can be referred to as the organic compound classes containing an ether group, an oxygen atom connected to two aryl or alkyl groups. They are rather nonpolar due to the presence of an alkyl group on either side of the central oxygen. There exist bulky alkyl groups adjacent to it means the oxygen atom is highly unable to participate in hydrogen bonding. It is a class of organic compounds, with a general formula of R-O-R, R-O-Ar or Ar-O-Ar, where “R” represents an alkyl group and “Ar” represents an aryl group. Here, we will learn about the physical and chemical properties of ethers.
Also check: Structure of amines
| Table of Contents |
Key Terms: Ether, Friedel Craft, Substitution, Symmetrical, Unsymmetrical Ether.
Structure of Ethers
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In the structure of ethers, the C-O-C linkage can be identified by the bond angles of 104.5 degrees, with the C-O distances being about 140 picometres. The ether's oxygen is more electronegative compared to the carbons. This is the reason why alpha hydrogens are more acidic than in the regular hydrocarbon chains.
Structure of Ethers
Also read: Structure of amines
Classification of Ethers
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Ethers are classified as –
- Symmetrical Ethers – Two identical groups are attached to the oxygen atom.
Ex. – Di-isopropyl Ether (CH3 – O – CH3)
Di-isopropyl Ether
- Unsymmetrical Ethers- Two different groups are attached to the oxygen atom.
Ex. – Ethyl methyl ether (CH3 – O – CH2 – CH3)
Ethyl methyl ether
Properties of Ethers
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Ethers are considered to be nonpolar due to presence of an alkyl group on either side of the central oxygen. Bulky alkyl groups are present adjacent to it, which means the oxygen atom is highly unable to participate in hydrogen bonding. This is the reason why ethers have lower boiling points compared to alcohols having the same molecular weight.
The physical and chemical properties of ether are given below.
Physical Properties of Ethers
- Due to the polarity of C-O bonds, the ether molecule has a net dipole moment.
- Despite the polarity of the C-O link, the boiling point of ethers is comparable to that of alkanes but significantly lower than that of alcohols of comparable molecular mass. The water miscibility of ethers is similar to that of alcohols.
- In water, ether molecules are miscible. This is due to the fact that the oxygen atom of ether, like that of alcohol, can form hydrogen bonds with a water molecule.
Chemical Properties of Ether
Ethers generally undergo chemical reactions in two ways:
- Cleavage of C-O bond:
Ethers are generally very unreactive in nature. When an excess of hydrogen halide is added to the ether, cleavage of C-O bond takes place leading to the formation of alkyl halides.
R-O-R + HX → RX + R-OH
Order of reactivity is given as HI>HBr>HCl
Electrophilic Substitution:
The alkoxy group in ether activates the aromatic ring at ortho and para positions for electrophilic substitution. Some of the common electrophilic substitution reactions are halogenation, Friedel Craft’s reaction etc.
Halogenation of Ethers:
Aromatic ethers undergo halogenation. For instance, Bromination - addition halogen in the presence or absence of a catalyst.
Friedel Craft’s Reaction of Ethers:
When an alkyl halide is treated with a Lewis acid in the presence of an aromatic ring, the alkyl group can be added to the ring (forming C-C) with the loss of a C-H bond. This electrophilic aromatic substitution reaction is known as the Friedel-Crafts alkylation reaction.
Alkyl Halide with Dry Silver Oxide:
When alkyl halide is treated with dry silver oxide, ether is produced
2C2H5Br + Ag2O → C2H5 – O – C2H5 + 2AgBr
Also read: Physical properties of amine
Uses of Ether
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- Dimethyl ether is applied as a refrigerant as well as a solvent at low temperatures.
- Diethyl ether is used in anaesthesia for surgeries as a common ingredient.
- It is a common solvent for oils, gums, resins etc.
- Ether is used along with petrol as a motor fuel.
- Phenyl ether can be applied as a heat transfer medium because of its high boiling point.
Ether Versus Ester
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The difference between ether and ester are as follows:
| Ester | Ether |
|---|---|
| Esters have the functional group –COO | Ethers have the functional group –O- |
| A double bond between carbon and oxygen atom | A single bond between carbon and oxygen atom |
| Derived from carboxylic acids | Derived from alcohol |
| Ex - Ethyl ethanoate | Ex- Dimethyl ether |
Things to Remember
- Ethers are organic compounds with a single bond between carbon and oxygen atom.
- Classification of Ethers - Symmetrical Ethers & Unsymmetrical Ethers
- The Ether molecule has a net dipole moment.
- Boiling point of ethers is lower than that of alcohols of comparable molecular mass.
- Water miscibility of ethers is similar to alcohols.
- Ether molecules are miscible in water.
- Cleavage of C-O bond - R-O-R + HX → RX + R-OH
- Electrophilic Substitution – a. Halogenation of Ethers b. Friedel Craft’s Reaction of Ethers
- Friedel Craft’s Reaction - An alkyl halide is treated with a Lewis acid in the presence of an aromatic ring, the alkyl group can be added to the ring (forming C-C) with the loss of a C-H bond
- Uses of Ether - Ether is used as a refrigerant, general anaesthetic, ether mixed with petrol as a motor fuel, and also used as a solvent for oils.
Sample Questions
Ques. Write Friedel Craft’s Reaction of Ethers. (2 marks)
Ans. Friedel-Crafts alkylation reaction is an electrophilic aromatic substitution reaction. An alkyl halide is treated with a Lewis acid in the presence of an aromatic ring, alkyl group can be added to the ring (forming C-C) with the loss of a C-H bond.
Ques. Classify Ethers. (2 marks)
Ans. Ethers are generally classified as
- Symmetrical Ethers – when two identical groups are attached to the oxygen atom.
Ex. – Di-isopropyl Ether
- Unsymmetrical Ethers- when two unidentical or different groups are attached to the oxygen atom.
Ex.- Ethyl methyl ether
Ques. Enlist the reaction an ether compound goes. (3 marks)
Ans. i. Cleavage of C-O bond - When Hydrogen halide is added to the ether, cleavage of C-O bond which leads to the formation of alkyl halides.
ii. Electrophilic Substitution – The alkoxy group in ether activates the aromatic ring at ortho (o) and para (p) positions for electrophilic substitution.
- Halogenation
- Friedel Craft’s Reaction or Friedel Craft’s Alkylation reaction
- Alkyl Halide with Dry Silver Oxide
Ques. What are the uses of Ether? (5 marks)
Ans. Some of the uses of Ether are as follows -
- Dimethyl ether is used as a refrigerant.
- Diethyl ether used as general anaesthetic.
- Ether is used along with petrol as a motor fuel.
- Diethyl ether used as a solvent for oils, gums, resins etc.
- Phenyl ether used as a heat transfer medium.
Ques. Write the difference between Ethers and Esters? (4 marks)
Ans.
| Ether | Ester |
|---|---|
| Ethers have the functional group –O- | Esters have the functional group –COO |
| A single bond between carbon and oxygen atom | A double bond between carbon and oxygen atom |
| Derived from alcohol | Derived from carboxylic acids |
| Ex- Dimethyl ether | Ex - Ethyl ethanoate |
Ques. Boiling point of ethyl alcohol is much higher than that of dimethyl ether though both have the same molecular weight. Why? (2 marks)
Ans. Alcohols have much higher boiling points than ethers because molecules of alcohols can interact through hydrogen bonding while molecules of ethers cannot.
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