Problem 150 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I (Reactants) 1\. \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{OH} \frac{\mathrm{NaBr}, \mathrm{H}_{2} \mathrm{SO}_{4}, \Delta}{\longrightarrow}\) 3\. \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH})\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3} \stackrel{\mathrm{PBr}_{3}}{\longrightarrow}\) 4\. \(\mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{OH} \stackrel{\mathrm{sOC}_{3}}{\longrightarrow}\) List II (Alkyl halides) A. \(\mathrm{CH}_{3} \mathrm{CHBr}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\) B. \(\mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{Cl}\) C. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}\) D. \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{Br}\) The correct matching is \(\begin{array}{rrrrr}1 & 2 & 3 & 4 \\ \text { (a) } \mathrm{C} & \mathrm{D} & \mathrm{B} & \mathrm{A}\end{array}\) (b) \(\mathrm{C} \quad \mathrm{D} \quad \mathrm{A} \quad \mathrm{B}\) (c) \(\mathrm{D} \quad \mathrm{C} \quad \mathrm{A} \quad \mathrm{B}\) (d) D \(\mathrm{C} \quad \mathrm{B} \quad \mathrm{A}\)

Step-by-Step Solution

Answer

The correct match is option (d): D C B A.

Step 1: Analyze Reactant 1

Reactant 1 is 1-butanol: \( \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{OH} \). When reacted with NaBr and \( \mathrm{H}_{2} \mathrm{SO}_{4}, \Delta \), it undergoes a nucleophilic substitution reaction to form 1-bromobutane: \( \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{Br} \). Thus, Reactant 1 matches with option D.

Step 2: Analyze Reactant 3

Reactant 3 is pentanol: \( \mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH})\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3} \). When reacted with \( \mathrm{PBr}_{3} \), it undergoes a nucleophilic substitution to form 2-bromopentane: \( \mathrm{CH}_{3} \mathrm{CHBr}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3} \). This matches with option A.

Step 3: Analyze Reactant 4

Reactant 4 is an isopropanol derivative: \( \mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{OH} \). When reacted with \( \mathrm{SOC}_{3} \), it undergoes substitution to form \( \mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{Cl} \), which is the option B.

Key Concepts

Nucleophilic Substitution

In organic chemistry, nucleophilic substitution reactions are fundamental mechanisms where a nucleophile selectively replaces a leaving group in a molecule. In the context of alkyl halide reactions, these processes are crucial.A typical nucleophilic substitution involves an alkane or alcohol, where a halide ion becomes the new substituent while ejecting an existing group—commonly a hydroxyl or halogen—into the surrounding solvent. This process often requires specific conditions such as acidic environments or specific reagents.For example, when 1-butanol (\(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{OH}\)) is treated with sodium bromide (NaBr) and sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)), it results in nucleophilic substitution wherein the hydroxyl group is replaced by a bromide to form 1-bromobutane (\(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{Br}\)). This example illustrates an important category of reactions that modify the structural and reactivity profile of organic compounds.

Organic Chemistry Reactions

Organic chemistry is filled with myriad reactions, each with unique reagents and conditions that govern the transformations of molecules. Alkyl halide synthesis through nucleophilic substitution exemplifies these chemical processes. Consider how primary, secondary, and tertiary alkyl groups impact the reaction mechanism and product outcome. A common reagent such as phosphorus tribromide (\(\mathrm{PBr}_{3}\)) can efficiently convert alcohols like pentanol (\(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH})\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\)) into alkyl bromides like 2-bromopentane (\(\mathrm{CH}_{3} \mathrm{CHBr}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\)) through a controlled substitution reaction.Moreover, the specific choice of reagents dictates not only the final product but also the efficiency and sustainability of the reaction. This quintessentially defines the diverse yet precise nature of organic chemistry reactions, serving as the backbone for synthesis in both academic studies and industrial applications.

Reaction Mechanism Analysis

Analyzing reactions through their mechanisms provides deep insights into how and why reactions occur. Imagine examining nucleophilic substitution in detail.Start by considering the role of each participant in the reaction. For instance, when \(\mathrm{SOC}_{3}\) interacts with an isopropanol derivative \(\mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{OH}\), it instigates a substitution that replaces the hydroxyl group with a chlorine ion, producing \(\mathrm{Me}_{2} \mathrm{CHCH}_{2} \mathrm{Cl}\). Here, the chlorine becomes the new substituent, illustrating the intricate steps underlying nucleophilic substitution.In each step, the intermediates formed reveal transition states that are crucial to understanding selectivity and kinetics. This approach, known as reaction mechanism analysis, enables chemists to design and optimize reactions for desired outcomes, a practice vital for both educational purposes and practical applications in fields like pharmaceutical development.