Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following compounds, which will react with acetone to give a product containing \(>\mathrm{C}=\mathrm{N}-?\) 1\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) 2\. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) 3\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHC}_{6} \mathrm{H}_{5}\) 4\. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHNH}_{2}\) (a) 3,4 (b) \(1,3,4\) (c) 1,3 (d) 1,4

Step-by-Step Solution

Answer

Option (d) 1,4

Step 1: Understand the Type of Reaction

The question asks which compound will react with acetone to form a product that contains the group \( > \mathrm{C}=\mathrm{N}- \). This is indicative of the formation of an imine, which occurs when a carbonyl group (from acetone) reacts with a primary amine (\( \mathrm{RNH}_2 \)).

Step 2: Evaluate Each Option for Presence of Primary Amines

To form an imine, the compound must contain a primary amine group. We need to check each given compound for a primary amine group \( \mathrm{NH}_2 \).

Step 3: Option 1 Analysis

\( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} \) contains a primary amine group and can potentially form an imine with acetone.

Step 4: Option 2 Analysis

\( (\mathrm{CH}_3)_3 \mathrm{~N} \) is a tertiary amine and does not have a primary amine group, hence it cannot form an imine.

Step 5: Option 3 Analysis

\( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHC}_{6} \mathrm{H}_{5} \) is a secondary amine (no free \( \mathrm{NH}_2 \) group) and cannot form an imine through the reaction with acetone.

Step 6: Option 4 Analysis

\( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHNH}_2 \) contains a \( \mathrm{NHNH}_2 \) group. The \( \mathrm{NH}_2 \) part is primary and can react with acetone to form an imine.

Step 7: Conclusion

From the analysis, both \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} \) and \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHNH}_2 \) have primary amine groups that can react with acetone. They correspond to options 1 and 4.

Key Concepts

Primary Amine

A primary amine is an organic compound that contains a basic nitrogen atom with a lone pair of electrons, bound to a single alkyl or aryl group. The general formula for a primary amine is \( \mathrm{RNH}_2 \), where \( \mathrm{R} \) represents an alkyl or aryl group, and \( \mathrm{NH}_2 \) is the amine functional group.

Primary amines are well-known for reactions involving the formation of imines. They are typically more reactive compared to secondary and tertiary amines.

• Primary amines are identified by the presence of one hydrogen atom bonded to a nitrogen atom.
• The lone pair of electrons on the nitrogen allows primary amines to act as nucleophiles.
• They easily participate in reactions with electrophiles, such as carbonyl groups, to form new compounds.

A practical example of this type of reaction involves the formation of an imine, which is an important intermediate in organic synthesis.

Carbonyl Group

The carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom (\(\mathrm{C=O}\)). This group is a common feature in many organic compounds, including ketones, aldehydes, and carboxylic acids.

The carbonyl group's significance lies in its electrophilic nature. This means the carbon atom in the group is positively charged due to its attachment to the more electronegative oxygen atom. This characteristic allows it to react readily with nucleophiles.

• The carbonyl carbon is a pivotal center in imine formation, reacting with primary amines.
• In this reaction, the oxygen atom of the carbonyl is replaced by the nitrogen of the amine, resulting in the \(\mathrm{C=N}\) double bond in imines.
• This process highlights the versatility and reactivity of the carbonyl group in organic reactions.

Ketones, such as acetone, provide an excellent example of a compound that contains a carbonyl group and reacts readily in these types of reactions.

Acetone Reaction

Acetone, also known scientifically as propanone, is one of the simplest and most common ketones. It contains a carbonyl group, making it reactive in a variety of organic chemistry reactions.

When acetone reacts with primary amines, such as aniline (\( \mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2 \)), an imine is formed:

• The reaction involves the nucleophilic attack of the nitrogen atom in the amine on the carbon atom of the carbonyl group.
• This results in the displacement of the oxygen atom, forming water and an imine product.
• This formation of an imine with acetone showcases the reactivity of carbonyl groups in ketones with primary amines.

Such reactions are critical in synthesizing varied organic compounds, showcasing both application and importance in organic chemistry.

Organic Chemistry Reactions

Organic chemistry reactions encompass a wide range of transformations that involve the making and breaking of bonds in organic compounds. Understanding these reactions requires familiarity with functional groups, such as amines and carbonyls, and their behavior.

Imine formation is one such reaction involving a nucleophilic primary amine attacking an electrophilic carbonyl group.

• Reactions like these are driven by the movement of electrons from areas of higher to lower electron density.
• This principle helps in forming new bonds and chemical structures.
• The knowledge of such reactions is important for developing new synthetic pathways that produce desired products efficiently.

By exploring these concepts, students deepen their understanding of molecular interactions and how they direct chemical transformations.