Which isomerism is shown by the following pairs?

\(CH_3CH_2CH_2OH\) and \(CH_3CH_2OCH_3\)

Functional isomerism

The correct answer is option 2. Functional isomerism.

Let us delve into the types of isomerism and specifically how they apply to the compounds \(CH_3CH_2CH_2OH\) and \(CH_3CH_2OCH_3\).

Types of Isomerism:

1. Position Isomerism:

This occurs when the same functional group is attached to different positions on the carbon chain.

Example: Consider butanol. You can have 1-butanol (\(CH_3CH_2CH_2CH_2OH\)) and 2-butanol (\(CH_3CH_2CH(OH)CH_3\)). Both have the -OH group, but in different positions on the carbon chain.

Not Applicable: In our case, one compound is an alcohol and the other is an ether, so they do not exhibit position isomerism.

2. Functional Isomerism:

Functional isomerism occurs when compounds have the same molecular formula but different functional groups. This results in different chemical properties because the functional groups determine the chemical reactivity and characteristics.

Example: Alcohols and ethers are functional isomers. For example, 1-butanol (\(CH_3CH_2CH_2CH_2OH\)) and ethyl methyl ether (\(CH_3CH_2OCH_3\)) both have the molecular formula \(C_5H_{12}O\) but differ in their functional groups. 1-Butanol has an -OH group (alcohol), while ethyl methyl ether has an -O- group (ether).

Applicable: Here, \(CH_3CH_2CH_2OH\) (an alcohol) and \(CH_3CH_2OCH_3\) (an ether) are functional isomers because they differ in their functional groups.

3. Structural Isomerism:

Structural isomerism is a broader category that includes various types of isomerism where compounds have the same molecular formula but different connectivity of atoms. This encompasses functional isomerism, positional isomerism, and chain isomerism.

Example: Butanol has several structural isomers including 1-butanol, 2-butanol, isobutanol, etc. Similarly, ethers like ethyl methyl ether differ from alcohols.

Applicable: Functional isomerism is a specific type of structural isomerism. Since \(CH_3CH_2CH_2OH\) and \(CH_3CH_2OCH_3\) are functional isomers, they are also structural isomers.

4. Chain Isomerism:

Chain isomerism occurs when the carbon chain is arranged differently, resulting in different structural forms (e.g., straight-chain vs. branched-chain isomers).

Example: For alkanes, butane (\(CH_3CH_2CH_2CH_3\)) and isobutane (\(CH_3CH(CH_3)CH_3\)) are chain isomers.

Not Applicable: The compounds \(CH_3CH_2CH_2OH\) and \(CH_3CH_2OCH_3\) do not differ in the arrangement of their carbon chains but in their functional groups, so they do not exhibit chain isomerism.

Conclusion:

The two compounds in question:

\(CH_3CH_2CH_2OH\) (1-butanol) is an alcohol with a hydroxyl group (-OH).

\(CH_3CH_2OCH_3\) (ethyl methyl ether) is an ether with an oxygen atom connecting two alkyl groups.

Since they have the same molecular formula (\(C_5H_{12}O\)) but different functional groups (alcohol vs. ether), they exhibit functional isomerism. They are also examples of structural isomerism in a broader sense because functional isomerism is a type of structural isomerism. However, functional isomerism is the most specific and appropriate term for their relationship.

Thus, the correct answer is 2. Functional Isomerism.