Problem 20 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following gives primary amine on reduction? (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NO}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{O}-\mathrm{N}=\mathrm{O}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{~N}=\mathrm{NC}_{6} \mathrm{H}_{5}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NC}\).

Step-by-Step Solution

Answer

Option (a) gives a primary amine on reduction.

Step 1: Understand Primary Amines

Primary amines have the general formula RNH2, where R is an alkyl or aryl group.

Step 2: Analyze Option (a)

The compound \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NO}_{2} \) is a nitro compound. Nitro compounds reduce to form amines, specifically primary amines, by replacing –NO2 with –NH2. Thus, this option can form a primary amine.

Step 3: Analyze Option (b)

The compound \( \mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{O}-\mathrm{N}=\mathrm{O} \) is a nitroso compound. Nitroso compounds typically do not reduce directly to primary amines under common conditions.

Step 4: Analyze Option (c)

The compound \( \mathrm{C}_{6} \mathrm{H}_{3} \mathrm{~N}=\mathrm{NC}_{6} \mathrm{H}_{5} \) is an azide. Azides can be reduced to form amines, but due to its complex aromatic structure, it may not easily or directly form a primary amine.

Step 5: Analyze Option (d)

The compound \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NC} \) is an isocyanide. Upon reduction, isocyanides can form secondary amines rather than primary amines by converting to R-NH-CH3 or others depending on conditions.

Step 6: Determine the Correct Option

Based on the analysis, option (a), \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NO}_{2} \), is the only compound that reduces to form a primary amine directly. It converts to \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \).

Key Concepts

Understanding Nitro Compounds

Nitro compounds are organic molecules characterized by the presence of one or more nitro functional groups \(-\mathrm{NO}_{2}\). Typically, nitro groups are attached to carbon atoms in the molecule’s backbone. Nitro compounds are prevalent in both industrial applications and everyday products, like explosives and solvents.

• The nitro group is a crucial moiety due to its impact on the molecular structure and reactivity.
• Nitro groups exhibit a unique ability to stabilize a variety of chemical reactions through electron withdrawal.

In essence, a nitro compound will have its properties determined by the characteristics of the -NO2 group, importantly influencing how these compounds behave during chemical transformations.

The Reduction Process Explained

The reduction process in chemistry typically involves the gain of electrons by a molecule, often transforming it into a more desirable product. In the context of nitro compounds, reduction is a method used to convert these compounds into amines. This transformation can be achieved using several reducing agents, such as hydrogen in the presence of a catalyst.

• Hydrogenation: A process using molecular hydrogen and catalysts like palladium or platinum.
• Metal-acid combinations: Utilizes metals such as iron or zinc in acidic conditions.

During reduction, the \(-\mathrm{NO}_{2}\) group is effectively "stripped down," leading to the formation of a \(-\mathrm{NH}_{2}\) group, which results in the creation of primary amines.

Exploring Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Understanding functional groups is essential for predicting and explaining various chemical behaviors.

• Nitro Group (\(-\mathrm{NO}_{2}\)): Related to nitro compounds, known for being electronegative and providing stability to compounds.
• Amino Group (\(-\mathrm{NH}_{2}\)): Found in amines, capable of participating in hydrogen bonding and making molecules basic.

Each functional group can be thought of as a 'signature' that greatly influences the molecule's properties and its interactions with other chemicals.

Amine Formation from Nitro Compounds

Amine formation from nitro compounds is a classic example of a reduction reaction in organic chemistry. Primary amines can be synthesized by reducing nitro groups, which involves the replacement of the \(-\mathrm{NO}_{2}\) functional group with an \(-\mathrm{NH}_{2}\) group.

• Primary amines are characterized by only one alkyl or aryl group attached to the amino nitrogen.
• The simplest example of this transformation is the reduction of nitroethane \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NO}_{2} \) to ethylamine \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \).

In this context, option (a) from the original exercise directly illustrates the ease of forming a primary amine through nitro compound reduction, demonstrating a key technique in producing vital organic compounds.