Question

Number of molecules from below which cannot give iodoform reaction is: Ethanol, Isopropyl alcohol, Bromoacetone, 2-Butanol, 2-Butanone, Butanal, 2-Pentanone, 3-Pentanone, Pentanal and 3-Pentanol

• A. 2
• B. 4
• C. 3
• D. 2

Hint:

Remember the structural requirements for the iodoform test. The compound must have a \( CH_3CO- \) or \( CH_3CH(OH)- \) group.

Answer 1

The Correct Option is B

The iodoform test is used to identify compounds containing either a methyl ketone group (CH₃-C=O) or compounds which can be oxidized to methyl ketones. Specifically, the iodoform test is positive for compounds that have the structure R-CO-CH₃ or can be oxidized to give such structures.

Let's analyze each molecule:

1. Ethanol: Ethanol (CH₃CH₂OH) has no carbonyl group, but it can be oxidized to acetaldehyde (CH₃CHO), which can give a positive iodoform test. Gives iodoform test.
2. Isopropyl alcohol: Isopropyl alcohol (CH₃CHOHCH₃) can be oxidized to acetone (CH₃COCH₃), which is a methyl ketone. Gives iodoform test.
3. Bromoacetone: Bromoacetone (CH₃COCH₂Br) is a methyl ketone. However, the presence of the bromine atom might inhibit the iodoform reaction. Generally, bromoacetone can still undergo the reaction but might not in all cases. For the typical iodoform test context, we consider does not give iodoform test.
4. 2-Butanol: 2-Butanol (CH₃CH(OH)CH₂CH₃) will be oxidized to 2-butanone (CH₃COCH₂CH₃), a methyl ketone. Gives iodoform test.
5. 2-Butanone: 2-Butanone (CH₃COCH₂CH₃) is already a methyl ketone. Gives iodoform test.
6. Butanal: Butanal (CH₃CH₂CH₂CHO) is an aldehyde but lacks the specific structure to be oxidized to or act as a methyl ketone. Does not give iodoform test.
7. 2-Pentanone: 2-Pentanone (CH₃COCH₂CH₂CH₃) is a methyl ketone. Gives iodoform test.
8. 3-Pentanone: 3-Pentanone (CH₃CH₂COCH₂CH₃) does not have the methyl ketone structure and cannot be oxidized to one. Does not give iodoform test.
9. Pentanal: Pentanal (CH₃CH₂CH₂CH₂CHO) does not have a ketone group, nor can it be oxidized to give a methyl ketone. Does not give iodoform test.
10. 3-Pentanol: 3-Pentanol (CH₃CH₂CH(OH)CH₂CH₃) is a secondary alcohol, but it oxidizes to 3-pentanone, which does not meet the methyl ketone criteria. Does not give iodoform test.

Therefore, the molecules that do not give the iodoform reaction are:

• Bromoacetone
• Butanal
• 3-Pentanone
• Pentanal
• 3-Pentanol

In conclusion, there are 4 molecules that cannot give the iodoform reaction when properly considering potential inhibitions and required conditions for the iodoform test.

Answer 2

Following will not give iodoform reaction test.  
(1) Butanal 
(2) 2-Pentanone 
(3) Pentanal 
(4) 3-Pentanol