Which one gives carbylamine reaction? (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NO}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) (d) \(\mathrm{CH}_{3} \mathrm{CONH}_{2}\)

In organic chemistry, primary amines are a class of nitrogen-containing compounds characterized by the presence of a nitrogen atom connected to one alkyl or aryl group and two hydrogen atoms. The general formula for a primary amine can be written as RNH2, where R represents an alkyl or aryl group.

Primary amines are versatile building blocks in organic synthesis and are involved in various chemical reactions. One such reaction is the carbylamine reaction, which is used to test for the presence of primary amines. In this reaction, a primary amine will react with chloroform (CHCl3) and an alkali base like potassium hydroxide, to produce a foul-smelling substance known as an isocyanide. This distinct odor provides a qualitative way to confirm the presence of a primary amine.

Importance of Primary Amines:

• They serve as intermediates in the synthesis of pharmaceuticals, dyes, and polymers.
• Primary amines play a critical role in biological systems, being part of the structure of amino acids and neurotransmitters.

The formation of isocyanides is a critical step in the carbylamine reaction. Isocyanides, also known as isonitriles, are organic compounds containing the functional group -N≡C:. This group defines their chemical behavior and reactivity.

During the carbylamine reaction, the primary amine reacts with chloroform in the presence of an alkali base to form the corresponding isocyanide. The general reaction mechanism involves the deprotonation of the primary amine to form an amide ion, which then attacks the chloroform. Subsequent steps lead to the elimination of three moles of hydrogen chloride and the formation of the isocyanide.

Here's a simplified version of the reaction mechanism:
1. RNH2 + KOH -> RNH- + H2O
2. RNH- + CHCl3 -> RNC + 3 HCl

The isocyanide's strong, unpleasant smell makes it easy to detect, providing a clear indication that a primary amine was present in the original compound.

A functional group in organic chemistry is a specific group of atoms within a molecule that determines the molecule's characteristic chemical reactions. Different functional groups confer different properties to molecules and define the types of chemical reactions they can undergo.

In the context of the carbylamine reaction, identifying the correct functional group is crucial. This reaction is specific to primary amines, which contain the functional group -NH2. However, similar-sounding functional groups like amides (-CONH2) do not undergo the carbylamine reaction. This is an important distinction for students to remember when analyzing organic compounds.

Key Points on Functional Groups:

• Functional groups are the reactive part of molecules and predict the pathway of chemical reactions.
• Understanding them helps in predicting physical properties and solubility patterns of organic compounds.
• Functional groups allow chemists to classify and organize organic compounds into families, making it easier to study their behavior.