Problem 112 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I List II 1\. \(\mathrm{CH}_{3} \mathrm{COOH}\) and \(\mathrm{HCOOCH}_{3}\) (i) metamers 2\. \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{CH}\) and (ii) position isomers \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\) 3\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) and (iii) tautomers \(\mathrm{CH}_{3}-\mathrm{CH}\left(\mathrm{NH}_{2}\right)-\mathrm{CH}_{3}\) 4\. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O}\) (iv) functional isomer The correct matching is: \(\begin{array}{llll}1 & 2 & 3 & 4\end{array}\) (a) (iii) (iv) (i) (iv) (b) (i) (ii) (iii) (iv) (c) (iii) (ii) (i) (iv) (d) (iv) (ii) (ii) (iv)

Step-by-Step Solution

Answer

Correct match is option (d): (iv), (ii), missing, (iv).

Step 1: Identify compound pairs

List the given pairs from List I and List II:1. \(\mathrm{CH}_{3}\mathrm{COOH}\) and \(\mathrm{HCOOCH}_{3}\)2. \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{CH}\) and \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\)3. \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{NH}_{2}\) and \(\mathrm{CH}_{3}-\mathrm{CH}\left(\mathrm{NH}_{2}\right)-\mathrm{CH}_{3}\)4. \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) and \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O}\)

Step 2: Pair 1 Analysis

Pair 1 contains \(\mathrm{CH}_{3}\mathrm{COOH}\) (acetic acid) and \(\mathrm{HCOOCH}_{3}\) (methyl formate). These compounds belong to different functional groups (carboxylic acid and ester), indicating they are functional isomers.

Step 3: Pair 2 Analysis

Pair 2 involves \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{CH}\) (butyne) and \(\mathrm{CH}_{3}-\mathrm{C}=\mathrm{C}-\mathrm{CH}_{3}\) (butene). The triple bond in butyne and the double bond in butene are at different positions. Therefore, they are position isomers.

Step 4: Pair 3 Analysis

The comparison of \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{NH}_{2}\) (propylamine) and \(\mathrm{CH}_{3}-\mathrm{CH}\left(\mathrm{NH}_{2}\right)-\mathrm{CH}_{3}\) (isopropylamine) shows that they are chain isomers, differing in structure of the carbon chain.

Step 5: Pair 4 Analysis

Given \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\) (ethyl alcohol) and \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O}\) (dimethyl ether), both have different functional groups (alcohol and ether), which are functional isomers.

Step 6: Match List I with List II

Combine the analyses: 1. (iv) related to functional isomer. 2. (ii) related to position isomer. 3. Not mentioned in any pair types; should be chain isomers not given. 4. (iv) related to functional isomer. Match the codes given - (d): 1(iv), 2(ii), 4(iv).

Key Concepts

Functional Isomers

In organic chemistry, functional isomers are compounds that share the same molecular formula but differ in their functional group classification. This means they have distinct properties and reactivity despite having identical numbers and types of atoms. A classic example encompasses the acetic acid (\(\mathrm{CH}_3\mathrm{COOH}\)) and methyl formate (\(\mathrm{HCOOCH}_3\)). Acetic acid contains a carboxylic acid group, while methyl formate is characterized by its ester group. Despite having the same molecular formula \(\mathrm{C}_2\mathrm{H}_4\mathrm{O}_2\), their functional group is entirely different, which directly influences their applications and reactions.

Position Isomers

Position isomers, also known as regioisomers, occur when compounds have the same molecular formula but differ in the position of a functional group or multiple bonds on the carbon skeleton. A classic example is found in the comparison of butyne (\(\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{C} \equiv \mathrm{CH}\)) and butene (\(\mathrm{CH}_3-\mathrm{C}=\mathrm{C}-\mathrm{CH}_3\)). In these compounds, the location of the double bond in butene has shifted position compared to the triple bond in butyne. This affects the physical and chemical properties, such as boiling points and reaction mechanisms. Position isomers play a crucial role in determining the behavior of molecules in chemical reactions.

Chain Isomers

Chain isomers are an interesting category of structural isomers, where compounds have the same molecular formula but differ in the branching of their carbon chains. This type of isomerism highlights compounds like propylamine (\(\mathrm{CH}_3\mathrm{CH}_2\mathrm{CH}_2\mathrm{NH}_2\)) and isopropylamine (\(\mathrm{CH}_3-\mathrm{CH}(\mathrm{NH}_2)-\mathrm{CH}_3\)). Though both molecules have the same formulas, \(\mathrm{C}_3\mathrm{H}_9\mathrm{N}\), the linear structure of propylamine differs from the branched structure of isopropylamine. The distinct arrangement leads to differences in properties, such as melting and boiling points. Chain isomers are essential in the study of hydrocarbons and larger organic compounds.

Metamers

Metamers are less commonly discussed but are noteworthy as they involve compounds sharing the same molecular formula and the same functional group, but differing in the distribution of carbon atoms around the functional group. While the original exercise does not include an example of metamers, they can typically be illustrated by compounds like diethyl ether and methyl propyl ether, each having an ether (\(-\mathrm{O}-\)) functional group, yet differing in how the carbon chains are positioned around it. This subtle difference can lead to variations in solubility and other chemical properties, thus metamers hold significance in the study of isomerism involving functional groups attached to different length carbon chains.

Tautomers

Tautomerism involves isomers of a compound that exist in dynamic equilibrium, differing mainly in the placement of a proton and the double bond. These structural rearrangements occur through the relocation of hydrogen atoms and electrons, leading to different compounds that swiftly interconvert. Considered as a special type of functional isomerism, tautomers are essential in understanding chemical reactivity and stability. A common example is the keto-enol tautomerism, such as acetone (\(\mathrm{CH}_3\mathrm{COCH}_3\)) interconverting with its enol form. Tautomers are crucial in biological processes and pharmaceutical design due to their unique ability to toggle between structures, impacting molecular functionality.