Q6 / 180 · COMEDK 2023 (Evening Shift) · Chemistry

Which one of the following compounds would not undergo Aldol condensation?

  • Correct answer
    A
    2,2-Dimethyl butanal
  • B
    2- Methyl pentanal
  • C
    1- Phenyl propanone.
  • D
    Phenyl ethanal

Solution

Aldol condensation requires the presence of at least one $\alpha$-hydrogen atom in the carbonyl compound. An $\alpha$-hydrogen is a hydrogen atom attached to the carbon atom adjacent to the carbonyl group.

Analyzing the structures:

1. 2,2-Dimethylbutanal: The structure is $CH_3-CH_2-C(CH_3)_2-CHO$. The $\alpha$-carbon is the carbon atom attached to the aldehyde group. In this molecule, the $\alpha$-carbon is bonded to two methyl groups and the aldehyde group, meaning it has no hydrogen atoms attached to it. Thus, it lacks $\alpha$-hydrogens.

2. 2-Methylpentanal: The structure is $CH_3-CH_2-CH_2-CH(CH_3)-CHO$. The $\alpha$-carbon has one hydrogen atom attached.

3. 1-Phenylpropanone: The structure is $C_6H_5-CO-CH_2-CH_3$. The $\alpha$-carbon (the carbon of the ethyl group attached to the carbonyl) has two hydrogen atoms.

4. Phenyl ethanal: The structure is $C_6H_5-CH_2-CHO$. The $\alpha$-carbon has two hydrogen atoms.

Since 2,2-Dimethylbutanal has no $\alpha$-hydrogen, it cannot undergo Aldol condensation.

Answer: 2,2-Dimethyl butanal

Hence, the correct answer is option: 'A'.

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