CBSE Class 12 Chemistry Chapter 13: Amines - Intext Questions Solutions

To classify amines as primary, secondary, or tertiary, we examine the number of alkyl or aryl groups directly attached to the nitrogen atom.

1. The structure is essentially NH₂, which implies it's part of a larger molecule where the nitrogen is attached to one carbon atom (e.g., CH₃NH₂). The nitrogen atom is bonded to only one carbon atom. Therefore, this represents a primary amine.

2. The structure is $N(CH\_3)\_2$. This indicates that the nitrogen atom is bonded to two methyl groups. Assuming it's part of a molecule like (CH₃)₂NH, the nitrogen is bonded to two carbon atoms. Therefore, this represents a secondary amine.

3. The structure is (C₂H₅)₂CHNH₂. Here, the amino group (-NH₂) is attached to a carbon atom which is itself attached to two ethyl groups and one hydrogen. The nitrogen atom is bonded to only one carbon atom (the one in the CH group). Therefore, this represents a primary amine.

4. The structure is $(C\_2H\_5)\_2NH$. The nitrogen atom is bonded to two ethyl groups and one hydrogen atom. Since the nitrogen atom is directly bonded to two carbon atoms (from the two ethyl groups), this represents a secondary amine.

Summary of Classification:

• Primary amines: (i) and (iii)
• Secondary amines: (iv)
• Tertiary amines: (ii)

The molecular formula $C\_4H\_\{11\}N$ corresponds to amines with four carbon atoms and eleven hydrogen atoms, plus one nitrogen atom. We need to find all possible structural arrangements (isomers) and their IUPAC names, and then identify the types of isomerism present between different pairs.

1. Structures and 2. IUPAC Names of Isomeric Amines (C₄H₁₁N):

We can systematically draw the isomers by considering the arrangement of the carbon chain and the position of the amino group.

1. Straight chain amines:

   • Structure: $CH\_3-CH\_2-CH\_2-CH\_2-NH\_2$
   • IUPAC Name: Butanamine (Primary amine)

2. Structure: $CH\_3-CH\_2-CH(NH\_2)-CH\_3$

   IUPAC Name: Butan-2-amine (Primary amine)

3. Structure: $CH\_3-CH(CH\_3)-CH\_2-NH\_2$

   IUPAC Name: 2-Methylpropan-1-amine (Primary amine)

4. Structure: $CH\_3-C(CH\_3)(NH\_2)-CH\_3$

   IUPAC Name: 2-Methylpropan-2-amine (Primary amine)

Secondary amines:

1. Structure: $CH\_3-CH\_2-CH\_2-NH-CH\_3$

   IUPAC Name: N-Methylpropan-1-amine (Secondary amine)

2. Structure: $CH\_3-CH\_2-NH-CH\_2-CH\_3$

   IUPAC Name: N-Ethylethanamine (Secondary amine)

3. Structure: $CH\_3-CH(CH\_3)-NH-CH\_3$

   IUPAC Name: N-Methylpropan-2-amine (Secondary amine)

Tertiary amines:

1. Structure: $CH\_3-CH\_2-N(CH\_3)\_2$

   IUPAC Name: N,N-Dimethylethanamine (Tertiary amine)

3. Types of Isomerism Exhibited:

We examine pairs of isomers to identify the type of isomerism.

• Chain Isomerism: Isomers with different carbon skeletons. For example, Butanamine (straight chain) and 2-Methylpropan-1-amine (branched chain) are chain isomers. Similarly, Butan-2-amine is also a chain isomer of these.
• Position Isomerism: Isomers with the same carbon skeleton but different positions of the functional group. For example, Butanamine (amino group at C1) and Butan-2-amine (amino group at C2) are position isomers. Also, N-Methylpropan-1-amine and N-Methylpropan-2-amine exhibit position isomerism with respect to the position of the methyl group on the nitrogen relative to the propyl chain.
• Functional Isomerism: Amines can be functional isomers with other classes of compounds like alcohols or ethers having the same molecular formula. For example, Butanamine (amine) is a functional isomer of Butanol (alcohol).
• Metamerism: This type of isomerism arises due to different alkyl chains attached to the same functional group. For secondary and tertiary amines, metamerism can be observed. For example, N-Methylpropan-1-amine ($CH\_3-CH\_2-CH\_2-NH-CH\_3$) and N-Ethylethanamine ($CH\_3-CH\_2-NH-CH\_2-CH\_3$) are metamers because the distribution of carbon atoms around the nitrogen atom is different (3+1 vs 2+2). N,N-Dimethylethanamine ($CH\_3-CH\_2-N(CH\_3)\_2$) is also a metamer with N-Methylpropan-1-amine and N-Ethylethanamine.

Specific examples from the question:

• Pairs exhibiting position isomerism: (a) Butanamine and (b) Butan-2-amine. Also, (e) N-Methylpropan-1-amine and (g) N-Methylpropan-2-amine.
• Pairs exhibiting chain isomerism: (a) Butanamine and (c) 2-Methylpropan-1-amine; (a) Butanamine and (d) 2-Methylpropan-2-amine; (b) Butan-2-amine and (c) 2-Methylpropan-1-amine; (b) Butan-2-amine and (d) 2-Methylpropan-2-amine.
• Pairs exhibiting metamerism: (e) N-Methylpropan-1-amine and (f) N-Ethylethanamine; (e) N-Methylpropan-1-amine and (h) N,N-Dimethylethanamine.
• All primary amines (a, b, c, d) exhibit functional isomerism with secondary amines (e, f, g) and tertiary amines (h).