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 detects compounds possessing a methyl ketone group (CH₃-C=O) or those oxidizable to methyl ketones. Specifically, a positive test results for structures R-CO-CH₃ or precursors to such structures.

Analysis of each molecule:

1. Ethanol: Ethanol (CH₃CH₂OH) oxidizes to acetaldehyde (CH₃CHO), yielding a positive iodoform test. Yields iodoform test.
2. Isopropyl alcohol: Isopropyl alcohol (CH₃CHOHCH₃) oxidizes to acetone (CH₃COCH₃), a methyl ketone. Yields iodoform test.
3. Bromoacetone: Bromoacetone (CH₃COCH₂Br), a methyl ketone, may exhibit inhibited reactivity due to the bromine atom. Typically considered to not yield iodoform test in standard contexts.
4. 2-Butanol: 2-Butanol (CH₃CH(OH)CH₂CH₃) oxidizes to 2-butanone (CH₃COCH₂CH₃), a methyl ketone. Yields iodoform test.
5. 2-Butanone: 2-Butanone (CH₃COCH₂CH₃) is a methyl ketone. Yields iodoform test.
6. Butanal: Butanal (CH₃CH₂CH₂CHO), an aldehyde, lacks the necessary structure for oxidation to or interaction as a methyl ketone. Does not yield iodoform test.
7. 2-Pentanone: 2-Pentanone (CH₃COCH₂CH₂CH₃) is a methyl ketone. Yields iodoform test.
8. 3-Pentanone: 3-Pentanone (CH₃CH₂COCH₂CH₃) lacks the methyl ketone structure and cannot be oxidized to one. Does not yield iodoform test.
9. Pentanal: Pentanal (CH₃CH₂CH₂CH₂CHO) has no ketone group and cannot be oxidized to a methyl ketone. Does not yield iodoform test.
10. 3-Pentanol: 3-Pentanol (CH₃CH₂CH(OH)CH₂CH₃), a secondary alcohol, oxidizes to 3-pentanone, which does not meet methyl ketone criteria. Does not yield iodoform test.

The molecules that do not yield the iodoform reaction are:

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

Consequently, 4 molecules are identified as not yielding the iodoform reaction when considering potential inhibitions and requisite conditions.