Question

Match the following: List 1 List 2 (Reagent) (Electrophiles) \(\oplus\) 1\. \(\mathrm{Cl}_{2}+\mathrm{AlCl}_{3}\) (1) \(\mathrm{NO}_{2}\) 2\. \(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4}\) (2) \(\mathrm{Cl} \ldots \mathrm{Cl} \ldots \mathrm{AlCl}_{3}\) or \(\mathrm{Cl}^{+}\) 3\. \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}\) (3) \(\mathrm{SO}_{3} \mathrm{H}\) (or \(\left.\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{SO}_{3}\right)\) 4\. \(\mathrm{Br}_{2}+\mathrm{Fe}\) (4) \(\mathrm{SO}_{3}\) (5) Br...Br...FeBr \(_{3}\) or \(\mathrm{Br}^{+}\) The correct matching is: \(\begin{array}{lll}1 & 2 & 3\end{array}\) 4 (a) (4) (3) (2) (b) (2) (1) (c) (2) (1) (d) (2) (3) (1) (4)

Short answer

(b) (2) (1) (4) (5) is the correct match.

Step-by-step solution

Analyze the options in List 1

Examine the reagents listed and identify the reactions they may undergo with their corresponding electrophiles. - **1.** \(\text{Cl}_{2} + \text{AlCl}_{3}\) is a reagent used to generate \(\text{Cl}^{+}\). - **2.** \(\text{HNO}_{3} + \text{H}_{2}\text{SO}_{4}\) is known to produce \(\text{NO}_{2}^{+}\) electrophiles. - **3.** \(\text{H}_{2} \text{S}_{2} \text{O}_{7}\) is equivalent to \(\text{H}_{2} \text{SO}_{4} + \text{SO}_{3}\) and forms the \(\text{SO}_{3} \) electrophile. - **4.** \(\text{Br}_{2} + \text{Fe}\) will generate \(\text{Br}^{+}\) as the electrophile.

Analyze the options in List 2

Examine the electrophiles in List 2 to match them with the corresponding reagent from List 1. - **(1) \(\text{NO}_{2}\) electrophile** is typically produced by the nitration reaction, where \(\text{HNO}_{3}\) and \(\text{H}_{2}\text{SO}_{4}\) are used. - **(2) \(\text{Cl}^{+}\) electrophile** is formed from \(\text{Cl}_{2}\) and \(\text{AlCl}_{3}\). - **(3) \(\text{SO}_{3} \) electrophile** is a product of \(\text{H}_{2} \text{S}_{2} \text{O}_{7}\). - **(4) \(\text{SO}_{3H}\)** electrophile corresponds to sulfonation, which uses \(\text{H}_{2} \text{S}_{2} \text{O}_{7}\). - **(5) \(\text{Br}^{+}\)** is generated from \(\text{Br}_{2}\) with the help of iron or a catalyst such as \(\text{FeBr}_{3}\).

Match reagents to electrophiles

Based on the analysis of both lists, perform the matching:- **1. \(\text{Cl}_{2} + \text{AlCl}_{3}\)** matches to **(2) \(\text{Cl}^{+}\)**. - **2. \(\text{HNO}_{3} + \text{H}_{2} \text{SO}_{4}\)** matches to **(1) \(\text{NO}_{2}^{+}\)** due to nitration. - **3. \(\text{H}_{2} \text{S}_{2} \text{O}_{7}\)** matches to **(4) \(\text{SO}_{3}\) electrophile** which it can generate.- **4. \(\text{Br}_{2} + \text{Fe}\)** matches to **(5) \(\text{Br}^{+}\)** since it helps in the bromination.

Key concepts

Electrophiles

In the realm of organic chemistry, electrophiles are key players. They are molecules or ions that seek out electrons due to their electron-deficient nature. Think of them as electron lovers! Electrophiles often possess a positive charge or have an atom that can readily accept electrons.

A typical example of an electrophile is \( ext{Cl}^{+}\), which is generated by the reagent \( ext{Cl}_2 + ext{AlCl}_3\). The aluminum chloride ( ext{AlCl}_3) helps to polarize \( ext{Cl}_2\), enabling one of the chlorine atoms to become a positively charged electrophile ready to react with electron-rich partners.

• Examples of Electrophiles: \( ext{NO}_2^+\), \( ext{SO}_3\), and \( ext{Br}^+\).
• These can result from various reactions such as nitration and sulfonation.

Electrophiles play a crucial role in mechanisms where they attack negatively charged or electron-rich centers in organic compounds, leading to the formation of new chemical bonds.

Reagents

Reagents are compounds or mixtures that cause a chemical reaction when mixed with other substances. They are like chemical tools that facilitate the creation or breaking of bonds.

In electrophilic reactions, reagents are the starting materials that interact to produce electrophiles. Take \( ext{HNO}_3 + ext{H}_2 ext{SO}_4\), for instance. In combination, these reagents produce the potent yet useful electrophile \( ext{NO}_2^+\).

• Other notable examples: \( ext{Br}_2 + ext{Fe}\) creates \( ext{Br}^+\), suitable for bromination.
• The mixture of \( ext{H}_2 ext{S}_2 ext{O}_7\) decomposes into \( ext{SO}_3\), crucial for sulfonation processes.

Reagents are the backbone of many chemical syntheses, providing the necessary components to drive reactions forward by forming intermediary species like electrophiles.

Nitration

Nitration is a classic example of an electrophilic aromatic substitution reaction. It involves the introduction of a nitro group \( ext{-NO}_2\) to an aromatic ring, such as benzene. This process uses two main reagents: nitric acid (\( ext{HNO}_3\)) and sulfuric acid (\( ext{H}_2 ext{SO}_4\)).

In this process, sulfuric acid acts as a catalyst, enhancing the electrophilic nature of the nitrate ion. The \( ext{HNO}_3\) donates a nitronium ion \( ext{NO}_2^+\), which is a strong electrophile that readily attacks aromatic rings, adding the nitro group.

• Importance: Nitration is pivotal in producing important compounds like dyes, pharmaceuticals, and explosives such as TNT.
• Nitration demonstrates the power of combining specific reagents to produce volatile electrophiles capable of significant chemical transformations.

By understanding nitration, chemists can effectively modify aromatic compounds, adding versatility to synthetic chemistry.

Sulfonation

Sulfonation is another important electrophilic aromatic substitution reaction. This reaction introduces a sulfonic acid group \( ext{-SO}_3H\) into aromatic compounds. The key reagent in this process is oleum, or fuming sulfuric acid, known as \( ext{H}_2 ext{S}_2 ext{O}_7\).

This powerful reagent yields the \( ext{SO}_3\) electrophile when dissolved in sulfuric acid. The \( ext{SO}_3\) is highly reactive and quickly adds to aromatic rings. In the case of sulfonation, the \( ext{SO}_3\) group is added, forming a sulfonic acid derivative.

• Applications: Sulfonation is used in creating detergents, dyes, and in the pharmaceutical industry.
• The reaction is both reversible and highly controllable, making it invaluable for producing custom sulfonic acid functionalities.

Understanding sulfonation allows chemists to strategically introduce functional groups, enhancing the properties and reactivity of aromatic compounds.