Comprehensive Guide to Ethers for Class 12 Chemistry NCERT

Introduction to and Ethers in Class 12 Chemistry

Ethers are an important class of organic compounds characterised by an oxygen atom connected to two alkyl or aryl groups, represented as R–O–R'. In your Class 12 NCERT syllabus, ethers are studied alongside alcohols due to their structural similarities and contrasting properties. Understanding ethers helps in grasping organic reaction mechanisms and their applications in pharmaceuticals and industry.

Preparation Methods of and Ethers

There are several ways to prepare ethers, but the most important ones for Class 12 students are:

• Williamson Ether Synthesis:
• React an alkoxide ion (RO⁻) with a primary alkyl halide (R'–X) via an SN2 reaction.
• Alkoxide ions are prepared by reacting alcohols with sodium metal or sodium hydride.
• This method allows synthesis of both symmetrical and unsymmetrical ethers but requires primary alkyl halides to avoid elimination.

• Dehydration of Alcohols:
• Two alcohol molecules react in the presence of concentrated sulfuric acid at about 140°C.
• Produces symmetrical ethers by protonation of the hydroxyl group, nucleophilic attack by another alcohol molecule, and loss of water.
• Not suitable for unsymmetrical ethers.

• Other Methods:
• Reaction of silver salts of carboxylic acids with alkyl halides.
• Reaction of phenols with alkyl halides under basic conditions to form aryl ethers.

Example:

$$\mathrm{C_2H_5ONa + C_2H_5Br \rightarrow C_2H_5OC_2H_5 + NaBr}$$

Williamson synthesis is versatile and widely used in organic synthesis.

Physical Properties of and Ethers

Ethers have unique physical properties that distinguish them from alcohols:

• Ethers are generally less polar than alcohols.
• They do not form hydrogen bonds with themselves but can accept hydrogen bonds from water, explaining their moderate solubility.
• Their boiling points are lower than alcohols of similar molecular weight.

These properties influence their use as solvents in organic reactions.

Chemical Reactions and Uses of and Ethers

Ethers are relatively inert but undergo some important reactions:

• Cleavage by HX (X = Cl, Br, I):
• Ethers react with hydrogen halides to form alkyl halides and alcohols.
• The reaction is faster with HI than HBr or HCl.

• Combustion:
• Like other hydrocarbons, ethers burn to produce CO2 and H2O.

• Uses:
• Common solvents in laboratories due to their low reactivity.
• Diethyl ether is used as an anaesthetic and solvent.
• Ethers serve as starting materials in organic synthesis.

Example:

$$\mathrm{C_2H_5OC_2H_5 + HBr \rightarrow C_2H_5Br + C_2H_5OH}$$

Understanding these reactions helps in predicting ether behaviour in chemical processes.

IUPAC Nomenclature of and Ethers

Naming ethers in Class 12 NCERT follows these rules:

• Identify the two alkyl or aryl groups attached to oxygen.
• Name the groups alphabetically followed by the word 'ether'.
• Alternatively, name the longer alkyl group as the parent and the other as an alkoxy substituent.

Examples:

• $\mathrm{C_6H_5–O–C_2H_5}$ is named ethoxybenzene or phenyl ethyl ether.
• $\mathrm{C_6H_5–O–C_7H_{15}}$ (n-heptyl) is n-heptyloxybenzene.

This systematic approach helps avoid confusion and ensures clarity in chemical communication.

Comparison Between Alcohols and and Ethers

Understanding differences between alcohols and ethers is crucial for Class 12 students. Here's a comparison:

This table helps clarify why ethers are often used as solvents and alcohols as reactants.