Question

Which among the following does not undergo Cannizzaro reaction?

• A. trimethylacetaldehye
• B. acetaldehyde
• C. benzaldehyde
• D. formaldehyde

Answer 1

The correct option is B

acetaldehyde

Explanation for correct option

(B)Acetaldehyde

Cannizzaro reaction

• Aldehydes that do not have an α-hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction on heating with concentrated alkali.
• In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidized to carboxylic acid salt.

Acetaldehyde

• The formula of acetaldehyde is ${\mathrm{CH}}_3\mathrm{CHO}$.
• The three hydrogens attached to carbon in acetaldehyde are alpha hydrogen.
• In acetaldehyde, alpha hydrogens are present. So, acetaldehyde does not undergo the Cannizzaro reaction.

Explanation for incorrect option

• The formula of trimethyl acetaldehyde is ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCHO}$. In this case, alpha hydrogen is not present.
• The formula of benzaldehyde is ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CHO}$. In this case, alpha hydrogen is not present.
• The formula of formaldehyde is $\mathrm{HCHO}$. In this case, alpha hydrogen is not present.
• Hence, trimethyl acetaldehyde, benzaldehyde, and formaldehyde undergo the Cannizzaro reaction due to the absence of alpha hydrogen.
• Hence, options (A), (C), and (D) are incorrect.

Option(B) is the correct answer. Acetaldehyde does not undergo a Cannizaro reaction.