Problem 115 - A Complete Resource Book in Chemistry for JEE Main

Question

A compound \(\mathrm{P}\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Cl}_{2}\right)\) on reaction with an alkali either gives a compound \(\mathrm{Q}\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right)\) or \(\mathrm{R}\left(\mathrm{C}_{3} \mathrm{H}_{4}\right)\). On oxidation, Q gives a compound \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2} . \mathrm{R}\), on reacting with dilute \(\mathrm{H}_{2} \mathrm{SO}_{4}\) containing \(\mathrm{Hg}^{2+}\) ion, gives a compound \(\mathrm{S}\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right)\), which reacts with bromine and alkali to give sodium salt of \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}\). Then \(\mathrm{P}\) is (a) \(\mathrm{CH}_{2} \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\) (b) \(\mathrm{CH}_{3} \mathrm{CCl}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CHClCH}_{2} \mathrm{Cl}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHCl}_{2}\)

Step-by-Step Solution

Answer

P is \( \mathrm{CH}_3\mathrm{CCl}_2\mathrm{CH}_3 \).

Step 1: Understand the Given Compounds

We start with the given compound \( P \) which has a formula \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{Cl}_{2} \). From reaction with an alkali, it can either give compound \( Q \) with formula \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \) or \( R \) with formula \( \mathrm{C}_{3}\mathrm{H}_{4} \). We need to deduce the possible structure of \( P \) such that these conditions are satisfied.

Step 2: Analyze Structure of Q and Corresponding Oxidation

Compound \( Q \) is \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \). There are various possibilities, such as propanal or acetone. Upon oxidation, \( Q \) yields \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}_{2} \), suggesting an alcohol like propan-1-ol oxidizing to propanoic acid or propanone oxidizing to acetic acid.

Step 3: Behavior of R with Sulfuric Acid

Compound \( R \) is \( \mathrm{C}_{3}\mathrm{H}_{4} \), which can describe propyne. Reaction with dilute \( \mathrm{H}_2\mathrm{SO}_4 \) containing \( \mathrm{Hg}^{2+} \) ion converts it to \( S, \) which is \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \), likely forming acetone or \( \mathrm{CH}_3\mathrm{COCH}_3 \).

Key Concepts

Chemical Reactions

Understanding the nature of chemical reactions is essential in organic chemistry. When a compound like \( \mathrm{P} \) reacts with an alkali, it can lead to the formation of different products. The reaction here can lead to two distinct compounds: \( \mathrm{Q} \) or \( \mathrm{R} \).
This reaction demonstrates the concept of elimination, where elements like hydrogen and halogens are removed. The specific pathway depends on the structure of \( P \) and the nature of the alkali used.
In the instance of \( \mathrm{Q} \), which has the formula \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \), it is evident that an elimination reaction has resulted in the formation of an organic compound containing an oxygen atom, indicative of either an alcohol or a ketone. On the other hand, the formation of \( \mathrm{R} \), with the formula \( \mathrm{C}_{3}\mathrm{H}_{4} \), suggests the creation of a compound through dehydrohalogenation, which hints at an unsaturated structure such as an alkyne.

Compound Identification

Compound identification in organic chemistry requires analyzing given formulas and potential structural possibilities. For instance, compound \( \mathrm{Q} \), with formula \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \), could be propanol or propanone. Upon oxidation, \( \mathrm{Q} \) results in \( \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}_{2} \). This pattern offers clues to its structure, as converting an alcohol to a carboxylic acid or a ketone to a dicarboxylic acid is common.
Identifying \( \mathrm{R}, \, \mathrm{C}_{3}\mathrm{H}_{4} \), might lead to considering structures like propyne, an alkyne. When reacting with sulfuric acid and a mercury ion catalyst, it forms an enol quickly rearranging into a stable carbonyl compound, which is \( \mathrm{S} \). Naming these possibilities is key in organic chemistry for clarity, accuracy, and understanding.

Structural Analysis

Structural analysis involves understanding how atoms are connected in space to determine a compound's overall characteristics and reactivity. Compounds \( Q \) and \( R \) must have specific structures to undergo the described reactions and transformations.

• The structure of \( Q, \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}, \) as an alcohol or ketone is essential, as the presence of a carbonyl group impacts its reactivity and the result of oxidation.
• \( R, \mathrm{C}_{3}\mathrm{H}_{4}, \) with potential alkyne configuration, influences how it reacts with sulfuric acid, forming \( \mathrm{S}, \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O} \), a possible ketone like acetone.

Structural analysis aids in determining the nature of \( P \), from which these products are derived. By analyzing each possible structural isomer, such as \( \mathrm{CH}_{2}\mathrm{ClCH}_{2}\mathrm{CH}_{2}\mathrm{Cl} \) versus \( \mathrm{CH}_{3}\mathrm{CHClCH}_{2}\mathrm{Cl} \), we can predict which compound conforms to the given reactions. This analysis helps in understanding the resulting possibilities, thereby refining the identification and characteristics of chemical structures involved.