Problem 32 - A Complete Resource Book in Chemistry for JEE Main

Question

Mark the correct statement: (a) methylamine is slightly acidic (b) methylamine is less basic than ammonia (c) methylamine is a stronger base than ammonia (d) methylamine forms salts with alkalies

Step-by-Step Solution

Answer

The correct statement is (c) methylamine is a stronger base than ammonia.

Step 1: Understand the Properties of Methylamine

Methylamine, CH₃NH₂, is an organic compound that contains an amino group where a methyl group replaces one hydrogen atom in ammonia (NH₃). This substitution modifies its properties compared to ammonia.

Step 2: Evaluate the Acidity of Methylamine

Assess the acidity of methylamine. Methylamine, like all amines, is classified as a base rather than an acid. Therefore, it is incorrect to state that it is slightly acidic, eliminating option (a).

Step 3: Compare Basicity of Methylamine and Ammonia

Consider basicity: Methylamine is a stronger base than ammonia because the methyl group is electron-releasing, which enhances the basicity of the nitrogen atom. This eliminates option (b) and supports option (c) as correct.

Step 4: Determine Salt Formation with Alkalies

Investigate salt formation: Methylamine, being basic, would not form salts with alkalies, which are also bases. Salts typically form when an acid reacts with a base. Thus, option (d) is incorrect.

Key Concepts

The Structure and Role of the Amino Group

Methylamine, known chemically as CH₃NH₂, includes a characteristic functional unit known as an amino group. An amino group typically comprises a nitrogen atom bonded to hydrogen atoms. In the case of methylamine, one of these hydrogens is replaced by a methyl group (CH₃).
This transformation uniquely distinguishes methylamine from ammonia, as it features:

• A bond between a nitrogen atom and a carbon atom from the methyl group
• A significantly different electronic and steric environment compared to ammonia

These characteristics significantly affect methylamine's chemical behavior and basicity, making it central to understanding its properties as an organic amine.

Understanding Basicity in Methylamine

Basicity refers to the ability of a molecule to accept a proton (H⁺) from an acid. In methylamine, this property is influenced by the methyl group connected to the nitrogen.
The methyl group is electron-releasing, enhancing the electron density on the nitrogen atom. This increased electron density makes the nitrogen more eager to accept a proton, boosting the basicity of methylamine.

• Higher electron density leads to increased readiness to gain protons
• Nitrogen's lone pair becomes more available for bonding with acids

Overall, the presence of the methyl group makes methylamine a stronger base compared to simple ammonia.

Methylamine as an Organic Compound

In chemistry, organic compounds are mainly characterized by the presence of carbon atoms. Methylamine fits this definition as it contains a carbon atom in its methyl group.
It displays the properties typical of amines, which are a subgroup of organic compounds featuring amino groups. This makes methylamine valuable in various industrial applications.

• Methylamine acts as a building block in organic synthesis
• It is used in producing pharmaceuticals and agricultural chemicals

Due to its reactive nature and ability to form bonds, methylamine is a versatile organic molecule with wide utility.

Comparing Methylamine and Ammonia

Ammonia (NH₃) and methylamine (CH₃NH₂) both contain nitrogen and hydrogen bonds, but the replacement of a hydrogen with a methyl group substantially changes their characteristics.
Although both are basic, methylamine is a stronger base than ammonia. This is due to the electron-releasing effect of the methyl group, which enhances the nitrogen's ability to capture protons.

• Both ammonia and methylamine can act as bases by donating a lone electron pair
• The methyl group increases electron cloud size around nitrogen

Thus, methylamine is more effective in protonation reactions, showing how slight structural differences can impact chemical behavior.