JEE Chemistry 2023 Question with Solution

Given: A list of six compounds is provided, and we need to count how many give a positive iodoform reaction.

Find: The number of compounds that contain the structural requirement for the iodoform test.

The iodoform test is positive for:

• methyl ketones having the group $\text{R-CO-CH}_3$
• secondary alcohols having the group $\text{R-CH(OH)-CH}_3$

A positive test gives yellow precipitate of $\text{CHI}_3$.

Now examine each compound one by one:

1. 1-Phenylbutan-2-one: This is a methyl ketone, represented as $\text{Ph-CH}_2\text{-CO-CH}_3$. Hence, it gives a positive test.

2. 2-Methylbutan-2-ol: This is a tertiary alcohol. It does not have the required $\text{CH}_3\text{CH(OH)-}$ arrangement. Hence, it does not give a positive test.

3. 3-Methylbutan-2-ol: This is a secondary alcohol containing the required methyl carbinol group. Hence, it gives a positive test.

4. 1-Phenylethanol: This is a secondary alcohol with structure $\text{Ph-CH(OH)-CH}_3$. Hence, it gives a positive test.

5. 3,3-dimethylbutan-2-one: This is a methyl ketone with structure $\text{CH}_3\text{-CO-C(CH}_3\text{)}_3$. Hence, it gives a positive test.

6. 1-Phenylpropan-2-ol: This is a secondary alcohol with structure $\text{Ph-CH}_2\text{-CH(OH)-CH}_3$. Hence, it gives a positive test.

Therefore, the compounds giving positive iodoform reaction are 1, 3, 4, 5, and 6.

So, the total number is $5$.

Given: The compounds must be tested for the functional group required in the iodoform test.

Find: Count of compounds containing either $\text{-COCH}_3$ or $\text{-CH(OH)CH}_3$.

Use the structural criterion:

Checking each entry:

Thus, the total number of compounds giving a positive iodoform test is $5$.