Problem 48 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The reagent with which both acetaldehyde and acetone react easily is [1981 - 1 Mark] (a) Fehling's reagent (b) Grignard reagent (c) Schiff's reagent (d) Tollen's reagent

Step-by-Step Solution

Answer

Grignard reagent (b) reacts with both acetaldehyde and acetone.

Step 1: Identify Relevant Information

Acetaldehyde is an aldehyde while acetone is a ketone. We need to determine which reagent reacts with both.

Step 2: Understanding Reagent Properties

Consider the properties of the given reagents: - **Fehling's reagent** is used to test for the presence of reducing sugars (i.e., aldehydes, but not ketones). - **Grignard reagents** generally react with aldehydes and ketones, forming alcohols. - **Schiff's reagent** is used as a test for aldehydes only. - **Tollen's reagent** is used to test for the presence of aldehydes only, not ketones.

Step 3: Analyze Compatibility with Both Compounds

Determine if each reagent reacts with both acetaldehyde (aldehyde) and acetone (ketone): - **Fehling's reagent** reacts with aldehydes but not ketones. - **Grignard reagents** react with both aldehydes and ketones, forming different types of alcohols. - **Schiff's reagent** reacts only with aldehydes. - **Tollen's reagent** also reacts only with aldehydes.

Step 4: Determine the Correct Reagent

Since the Grignard reagent reacts with both aldehydes and ketones, it is the correct answer.

Key Concepts

Acetaldehyde

Acetaldehyde, known as ethanal, belongs to a class of organic compounds known as aldehydes. It is a simple, yet crucial building block in organic chemistry. This compound is characterized by the presence of a carbonyl group (C=O) bonded to at least one hydrogen atom. Acetaldehyde is commonly found as a byproduct in plants, ripe fruits, cigarette smoke, and even gasoline exhaust. Its simple structure allows it to participate in a variety of chemical reactions.

Some interesting properties of acetaldehyde include:

• It is a clear, colorless liquid that is highly flammable.
• It has a distinctive, sharp, fruity smell.
• It serves as an intermediate in the synthesis of various chemicals and perfumes.
• It readily undergoes oxidation to form acetic acid.

Acetaldehyde plays a crucial role in organic reactions, where it can be used to form polymers and various alcohols, particularly when reacting with reagents like the Grignard reagent. This makes it a valuable compound in both industrial applications and laboratory research.

Acetone

Acetone, scientifically known as propanone, is the simplest and most widely used ketone. Unlike aldehydes, acetone contains a carbonyl group (C=O) bonded to two carbon atoms. This structural difference gives acetone its distinct properties.

Some key characteristics of acetone include:

• It is a colorless, volatile, and flammable liquid.
• It has a sweet, pungent smell often associated with nail polish remover.
• It is extensively used as a solvent in the production of plastics and other industrial products.
• It can dissolve both polar and non-polar substances, making it a versatile cleaning agent.

In organic chemistry, acetone is a fundamental component due to its ability to engage in various reactions. When acetone reacts with Grignard reagents, it forms tertiary alcohols, further highlighting acetone's importance in synthetic chemistry.

Reagent Properties

Reagents in chemistry are substances or compounds added to a system to cause a chemical reaction, or to test if a reaction occurs. Each reagent has its unique properties that dictate its reactivity with different classes of chemicals.

Understanding the properties of these reagents can simplify many reaction processes. Key properties and uses include:

• **Fehling's reagent** is specifically used to detect aldehydes. It gives a positive test for reducing sugars but does not react with ketones like acetone.
• **Grignard reagents** are organomagnesium compounds that react with both aldehydes and ketones to form alcohols, making them highly versatile in synthesis.
• **Schiff's reagent** reacts with aldehydes to form a colored complex, primarily used for aldehyde detection.
• **Tollen's reagent** is another tool for confirming the presence of aldehydes, forming a silver mirror upon reaction.

These properties make the Grignard reagent particularly special, as it can react with both acetaldehydes and ketones like acetone. This dual reactivity pattern is essential for many industrial processes and academic studies, as it allows for the formation of various alcohol compounds from simple carbonyl sources.