Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Victor Meyer test is not given by (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\)

Step-by-Step Solution

Answer

Option (b) \((\mathrm{CH}_{3})_{3} \mathrm{COH}\) does not give the Victor Meyer test.

Step 1: Understand the Victor Meyer Test

The Victor Meyer test is used to distinguish between primary, secondary, and tertiary alcohols. A primary alcohol gives a blue solution, a secondary alcohol gives a red solution, while a tertiary alcohol does not react and remains colorless.

Step 2: Identify the Type of Alcohol for Each Option

Determine whether each option is a primary, secondary, or tertiary alcohol:- (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) is a primary alcohol.- (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\) is a tertiary alcohol.- (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) is a primary alcohol.- (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\) is a secondary alcohol.

Step 3: Determine Which Alcohol Does Not React in the Test

Since the tertiary alcohol does not react in the Victor Meyer test, identify the option that is a tertiary alcohol and does not give the test outcome (color change).

Step 4: Conclusion

Option (b), \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\), is a tertiary alcohol and does not give the Victor Meyer test. Therefore, it is the correct answer.

Key Concepts

Primary Alcohol

A primary alcohol is characterized by its structure, where the hydroxyl group is attached to a carbon atom that is also only bonded to one other carbon atom. This means the structure is such that the alcohol group (OH) is on a carbon at the end of a chain.

• For example, ethanol and propanol are primary alcohols.

In the Victor Meyer test, primary alcohols produce a blue solution. This test involves the derivation of the alcohol into its corresponding iodide, followed by Hoffman's reaction, and finally the Meyer reaction which is a color development phase. This color change helps in identifying the alcohol as primary.

Secondary Alcohol

Secondary alcohols have their hydroxyl group bonded to a carbon that is itself attached to two other carbon atoms. This usually places the alcohol group in the middle of a carbon chain.

• An example of a secondary alcohol is isopropanol .

When these types of alcohol are subjected to the Victor Meyer test, they yield a red color. The test identifies secondary alcohols through similar steps as with primary, but the red color formation distinguishes them clearly from the blue of primary and the lack of color with tertiary.

Tertiary Alcohol

A tertiary alcohol has its hydroxyl group attached to a carbon that connects with three other carbons. This structural difference results in distinct chemical behavior.

• An instance is tert-butanol .

In the Victor Meyer test, tertiary alcohols do not yield any color change, indicating their unique reaction pathway compared to primary and secondary alcohols. This lack of color change arises because tertiary alcohols do not form intermediate iodides easily due to steric hindrance, hence they remain unreacted.

Alcohol Classification

Alcohols are classified based on which type of carbon atom the hydroxyl group is attached to. Understanding this classification allows chemists to predict and identify the reactivity and behavior of alcohols in chemical reactions.

• Primary Alcohols: The hydroxyl group is connected to a carbon bonded to only one other carbon atom.
• Secondary Alcohols: The hydroxyl group is attached to a carbon bonded to two other carbon atoms.
• Tertiary Alcohols: Here, the hydroxyl group is on a carbon attached to three other carbons.

This classification is essential in the Victor Meyer test as it determines the kind of color change observed, helping in differentiating between these classes. Primary turns blue, secondary turns red, and tertiary remains colorless in the test.