Problem 52 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Among the following compounds, which will react with acetone to give a product containing \(>\mathrm{C}=\mathrm{N}\)-bond ?(a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHC}_{6} \mathrm{H}_{5}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHNH}_{2}\).

Step-by-Step Solution

Answer

Options (a) \(\text{C}_6\text{H}_5\text{NH}_2\) and (d) \(\text{C}_6\text{H}_5\text{NHNH}_2\) will react with acetone.

Step 1: Identify the Reactants

Firstly, recognize what acetone is and the functional group involved. Acetone is a simple ketone with the formula \(\text{C}_3\text{H}_6\text{O}\). It contains a carbonyl group \((\text{C}=\text{O})\) that can undergo reactions with nucleophiles.

Step 2: Understand the Reaction Requirements

Realize that to form a C=N bond, acetone must react with a nucleophile that possesses a primary amine \((\text{RNH}_2)\). This is because the nucleophile needs a hydrogen that can be lost to form the double bond.

Step 3: Analyze Each Option

- For option (a) \( \text{C}_6\text{H}_5\text{NH}_2 \) - this is an aniline, which has a primary amine group. - For option (b) \( (\text{CH}_3)_3\text{N} \) - this is a tertiary amine and lacks hydrogen on nitrogen.- For option (c) \( \text{C}_6\text{H}_5 \text{NHC}_6\text{H}_5 \) - this is a secondary amine and lacks the necessary hydrogen.- For option (d) \( \text{C}_6\text{H}_5\text{NHNH}_2 \) - this is phenylhydrazine, which also contains a primary amine group.

Step 4: Determine Candidates for Reaction

Based on the analysis, compounds (a) and (d) can react with acetone because they contain a primary amine group, which is necessary to form the C=N bond.

Step 5: Final Selection

Considering all options, only (a) \( \text{C}_6\text{H}_5\text{NH}_2 \) and (d) \( \text{C}_6\text{H}_5\text{NHNH}_2 \) will react with acetone to give a product containing \(>\text{C}=\text{N}\)-bond.

Key Concepts

Carbonyl Group Reactions

Carbonyl group reactions are fascinating and involve the chemistry of compounds containing the carbonyl group (\(C=O\)). Acetone, a simple ketone, is a classic example.
This group is reactive due to the polar nature of the carbonyl bond. Oxygen is electronegative, pulling electron density away from carbon, making carbon electrophilic.

Because of this electrophilicity, carbonyl groups are prone to nucleophilic attacks. This is one of the key features in the reactivity of carbonyl compounds like acetone.

• In these reactions, a nucleophile donates electron pairs to the electrophilic carbon of the carbonyl group.
• This tendency allows various transformations, such as forming imines (\(C=N\) bonds).
• For instance, upon reacting with nucleophiles possessing amino groups, such as primary amines, carbonyls can form stable compounds through condensation reactions.

Understanding the behavior of the carbonyl group in these reactions is crucial, particularly in organic synthesis and JEE Advanced Chemistry topics.

Nucleophilic Reactions

Nucleophilic reactions involve species called nucleophiles, which are either negatively charged or neutral molecules with a lone pair of electrons. These electrons can be donated to an electrophile, forming a bond.
In the context of carbonyl chemistry, nucleophiles are often drawn to the partial positive charge on the carbon of the carbonyl group.

Such nucleophilic attacks can initiate a variety of reactions.

• Nucleophiles in the form of amines can react with carbonyl compounds resulting in the formation of amides, imines, or related products.
• The reaction follows a mechanism whereby the nucleophile attacks the carbonyl carbon, leading to the opening of the double bond.
• In the presence of a primary amine, it facilitates the formation of \(C=N\) bonds through subsequent steps of protonation and dehydration.

This concept of nucleophilicity is central to reactions involving acetone and other carbonyl chemicals, especially important for students preparing for competitive exams like JEE Advanced.

Primary Amines

Primary amines are molecules that contain the \(-NH_2\) group linked to a carbon atom. These compounds are notable for their ability to form a variety of important chemical bonds.

When primary amines react with carbonyl compounds, a type of nucleophilic reaction can occur leading to the formation of an imine product.

• Aniline (\(C_6H_5NH_2\)) is an example of a primary amine that can react with carbonyl groups in aldehydes or ketones such as acetone to form \(C=N\) bonds.
• This occurs because primary amines have hydrogens attached to the nitrogen, which are necessary for dehydration after the initial nucleophilic attack.
• In these reactions, the nitrogen of the amine actively binds with the electrophilic carbon of the carbonyl, leading to dehydration and formation of a double bond.

Understanding the role that primary amines play in organic reactions, like those involving nucleophilic acyl substitution, is significant for students studying advanced chemistry concepts.