Question

Among the following, the number of compounds which will give positive iodoform reaction is ____ .
(a) 1-Phenylbutan-2-one 
(b) 2-Methylbutan-2-ol 
(c) 3-Methylbutan-2-ol 
(d) 1-Phenylethanol 
(e) 3,3-dimethylbutan-2-one 
(f) 1-Phenylpropan-2-ol

Answer 1

Correct Answer: 4

Iodoform Test Analysis 

The iodoform test is a qualitative test for the presence of methyl ketones (R-CO-CH3) and certain secondary alcohols (R-CH(OH)-CH3). A positive iodoform test results in the formation of a yellow precipitate of iodoform (CHI3).

The necessary structural feature for a positive iodoform test is the presence of a methyl ketone group (CH3C=O) or a methyl carbinol group (CH3CH(OH)-).

Let’s examine each compound:

• (a) 1-Phenylbutan-2-one: This is a methyl ketone (Ph-CH2-CO-CH3) and will give a positive iodoform test.
• (b) 2-Methylbutan-2-ol: This is a tertiary alcohol and will not give a positive iodoform test.
• (c) 3-Methylbutan-2-ol: This is a secondary alcohol with the required CH3CH(OH)- group, so it will give a positive iodoform test.
• (d) 1-Phenylethanol: This is a secondary alcohol with the required CH3CH(OH)- group (Ph-CH(OH)-CH3), so it will give a positive iodoform test.
• (e) 3,3-dimethylbutan-2-one: This is a methyl ketone (CH3-CO-C(CH3)3), so it will give a positive iodoform test.
• (f) 1-Phenylpropan-2-ol: This is a secondary alcohol with the required CH3CH(OH)- group (Ph-CH2-CH(OH)-CH3) and will give a positive iodoform test.

Conclusion:

Therefore, four compounds (a, c, d, and f) will give a positive iodoform reaction.