Problem 123 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I List II (Reagents) (Nature) 1\. \((\mathrm{CN})\) (i) Neutral nucleophile 2\. (ONO) (ii) electrophile 3\. \(\mathrm{NH}_{3}\) (iii) Ambident nucleophile 4\. \(\mathrm{AlCl}_{3}\) (iv) both El and Nu The correct matching is: 1 \(2 \quad 3\) 4 (a) (i) (iii) (ii) (iv) (b) (iii) (iii) (i) (ii) (c) (iv) (iii) (iii) (i) (d) (ii) (iv) (i) (iii)

Step-by-Step Solution

Answer

Option (b) is the correct match.

Step 1: Understand the Nature of Each Reagent

To solve the matching problem, first identify the nature of each reagent from List I: - \(\text{CN}\) is a negatively charged group, known as a nucleophile, but it can attack at two sites, carbon or nitrogen, making it an ambident nucleophile.- \(\text{ONO}\) usually refers to organic nitrites, which can act as nucleophiles with two possible attack points (ambident nucleophile).- \(\text{NH}_{3}\) is a well-known neutral nucleophile, often used in substitution reactions where it donates a pair of electrons.- \(\text{AlCl}_{3}\) is an electron-deficient compound, often acting as an electrophile or Lewis acid.

Step 2: Match Based on Recognized Chemical Behavior

Based on the understanding of chemical behavior of each reagent from Step 1, match them with their corresponding types in List II:1. \(\text{CN}\) -> Ambident nucleophile (iii) 2. \(\text{ONO}\) -> Ambident nucleophile (iii) 3. \(\text{NH}_{3}\) -> Neutral nucleophile (i)4. \(\text{AlCl}_{3}\) -> Electrophile (ii)

Step 3: Select the Correct Matching from Options

Examine the options provided to find the one that matches the determinations made in Step 2: - Option (a): 1 (i), 2 (iii), 3 (ii), 4 (iv) does not match. - Option (b): 1 (iii), 2 (iii), 3 (i), 4 (ii) matches perfectly with our determinations. - Option (c) and Option (d) incorrectly describe some of the reagent behaviors. Thus, Option (b) is the correct match from List I to List II.

Key Concepts

Reagents

Reagents are chemical substances used in reactions to produce specific outcomes. They are integral in both organic and inorganic chemistry for facilitating chemical transformations. Reagents come in various forms, including:

• Liquids such as sulfuric acid.
• Solids like sodium chloride.
• Gases for instance, chlorine.

They can function as catalysts, where they are not directly consumed in the reaction, or as reactants that participate actively. Understanding the nature of reagents is crucial as they dictate the course and outcome of a reaction.
For example, a reagent like \(\text{AlCl}_3\) acts as a Lewis acid, accepting electron pairs, which makes it an electrophile.

Ambident Nucleophile

Ambident nucleophiles are unique because they can form bonds at two different atoms within the same molecule. The term 'ambident' comes from the Latin words 'ambi,' meaning both, and 'dentate,' meaning 'toothed or pointed.' Thus, ambident nucleophiles have two "teeth" or active sites for bonding.
An excellent example is the cyanide ion (\(\text{CN}^-\)), which can react through the carbon atom (acting as a carboanion) or the nitrogen atom (acting as a nitranion). This versatility allows ambident nucleophiles to form different products based on the reaction conditions.
Knowing which site will attack can be influenced by factors such as:

• Solvent effects.
• Temperature.
• Reagent stability.

Electrophiles

Electrophiles are atoms or molecules that seek electrons and are electron-deficient. They play a fundamental role in chemical reactions by accepting electron pairs from nucleophiles.
In chemistry, understanding the nature of electrophiles is crucial because they often initiate reactions, particularly in organic chemistry. For example, \(\text{AlCl}_3\) is a common electrophile used in various chemical reactions like Friedel-Crafts alkylation and acylation.

• Electrophiles have empty orbitals which allow them to form new chemical bonds.
• They often have a positive charge or are neutral but polarized.

A strong electrophile will attract a nucleophile, facilitating the flow of electrons from the nucleophile to the electrophile.

Nucleophiles

Nucleophiles are chemical species that donate an electron pair to an electrophile to form a chemical bond. The name comes from the Latin words 'nucleus,' meaning kernel or core, and 'philia,' meaning fondness. So, nucleophiles "love" nuclei, or positively charged centers.
These species are essential in many organic reactions, as they attack sites that are electron-deficient. Ammonia (\(\text{NH}_3\)) is a typical example of a neutral nucleophile, making it quite stable and very effective in substitution reactions.

• Nucleophiles typically have a full negative charge or a lone pair of electrons.
• Examples include hydroxide ions (\(\text{OH}^-\)), and halide ions (\(\text{Cl}^-\), \(\text{Br}^-\)).