Problem 17 - A Complete Resource Book in Chemistry for JEE Main

Question

An organic compound 'A' having molecular formula \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~N}\), on reduction gave another compound 'B'. Upon treatment with nitrous acid, 'B' gave ethyl alcohol. On warming with chloroform and alcoholic KOH, it formed an effensive smelling compound ' \(\mathrm{C}\) '. The compound ' \(\mathrm{C}^{\prime}\) is (a) \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{N}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~N} \equiv \mathrm{C}\)

Step-by-Step Solution

Answer

The compound 'C' is \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{~N} \equiv \mathrm{C} \) (option d).

Step 1: Determine Compound A

Compound 'A' has the molecular formula \( \mathrm{C}_2 \mathrm{H}_3 \mathrm{N} \). The most likely structure for this formula is \( \mathrm{CH}_3 \mathrm{C} \equiv \mathrm{N} \), which is acetonitrile.

Step 2: Reduction of Compound A

When acetonitrile (\( \mathrm{CH}_3 \mathrm{C} \equiv \mathrm{N} \)) is reduced, it forms \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2 \), which is ethylamine, labeled as compound 'B'.

Step 3: Reaction of Compound B with Nitrous Acid

When ethylamine \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2 \) reacts with nitrous acid, it forms ethyl alcohol \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH} \), confirming that 'B' was correctly identified.

Step 4: Reaction of Compound B with Chloroform and KOH

When ethylamine \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2 \) is treated with chloroform and alcoholic KOH, it forms an offensive-smelling compound known as isocyanide or carbylamine, \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NC} \), labeled as compound 'C'.

Step 5: Identify Compound C

The compound formed in Step 4 is an isocyanide, specifically ethyl isocyanide \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{~N} \equiv \mathrm{C} \). Therefore, option (d) is the compound 'C'.

Key Concepts

Organic Compounds

Organic compounds are the building blocks of life and chemistry. They primarily consist of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. This carbon-based framework allows for a vast array of molecular structures and functions.
One interesting aspect of organic compounds is their ability to form isomers. Isomers are molecules that share the same molecular formula but differ in structure. This can lead to different chemical and physical properties.
For instance, in the exercise, we have acetonitrile with the molecular formula \( \mathrm{C}_2 \mathrm{H}_3 \mathrm{N} \). Although other structures could exist with the same formula, acetonitrile is the simplest linear structure.
Organic compounds also exhibit various functional groups, which are specific groups of atoms within molecules that are responsible for characteristic chemical reactions. Acetonitrile contains a nitrile group (\(-\mathrm{C} \equiv \mathrm{N}\)), bringing a unique reactivity to the compound.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. They are central to organic chemistry and dictate how molecules change upon reacting with other substances.
In our exercise, acetonitrile undergoes several reactions. One of the key transformations is its reduction to ethylamine.

• Reduction reactions typically involve the gain of electrons or removal of oxygen.
• In this case, it involves the addition of hydrogen to acetonitrile, converting the nitrile group into an amine group.

Another important reaction in the exercise is the reaction of ethylamine with nitrous acid, which produces ethyl alcohol and nitrogen gas. This transformation highlights the functional group interconversion that occurs in organic chemistry.
Lastly, the reaction with chloroform and alcoholic KOH is specific to amines, showing the creation of the pungent-smelling isocyanide, demonstrating the practicality of these reactions in identifying functional groups.

Molecular Formula

The molecular formula is a concise way to represent the number and types of atoms in a molecule. For example, \( \mathrm{C}_2 \mathrm{H}_3 \mathrm{N} \) tells us that the molecule consists of 2 carbon atoms, 3 hydrogen atoms, and one nitrogen atom.
Understanding molecular formulas is crucial in identifying organic compounds, as they provide insight into the possible structures and functionalities of the compound. Molecular formulas can sometimes be deceptive without structural information; isomers might share the same formula but have vastly different structures.
In the exercise, the molecular formula helps narrow down potential structures for compound 'A'. It aids chemists in deducing that the linear structure of acetonitrile is most likely given the simplicity and likelihood compared to its isomers.
Interpreting molecular formulas also assists in predicting the type of chemical reactions a compound may undergo, as seen with the transformations from acetonitrile to ethylamine, and finally to ethyl alcohol and ethyl isocyanide.

Reduction Reactions

Reduction reactions are a fundamental type of chemical reaction where substances gain electrons, often accompanied by the addition of hydrogen or the removal of oxygen. In organic chemistry, reduction reactions can transform functional groups, significantly altering a compound's chemical properties.
A classic example is the reduction of the nitrile group \(-\mathrm{C} \equiv \mathrm{N}\) in acetonitrile to a primary amine group \(-\mathrm{NH}_2\) in ethylamine. This transformation involves the addition of hydrogen to break a triple bond and form new single bonds.
Reduction reactions are not only pivotal for creating amines from nitriles but also play a crucial role in various organic synthesis processes. They provide pathways to convert more complex molecules into simpler, more reactive ones.

• Such reactions often require catalysts like metal hydrides or hydrogen gas in the presence of specific conditions.
• These reactions are essential in industries like pharmaceuticals, where they've been utilized to synthesize active pharmaceutical ingredients.

The ability to manipulate reduction reactions allows chemists to create a wide range of compounds from basic organic structures, showcasing the versatility and importance of this chemical process.