Question

Which among the following does not undergo Cannizaro reaction?
(A)Trimethylacetaldehyde
(B)Acetaldehyde
(C)Benzaldehyde
(D)Formaldehyde

Answer 1

Hint :To answer this question we should have the proper knowledge of Cannizaro reaction. There are two molecules of aldehyde in Cannizaro reaction which undergo a redox reaction and form a primary alcohol and a carboxylic acid by the use of a hydroxide base. The detailed solution is given below.

Complete Step By Step Answer:
Acetaldehyde does not give Cannizaro reaction. The reason for this is that acetaldehyde contains three alpha hydrogen. The Cannizaro reaction takes place when there is no alpha hydrogen present in the molecule. Alpha hydrogen is always bonded with alpha carbon which is the first carbon bonded with a functional group. The structure of acetaldehyde is $ C{H_3} - CHO $ . So you can clearly see that it contains 3 alpha hydrogens. Now, we are going to see that how the reaction takes place: $ 2C{H_3} - CHO + NaOH \to C{H_3}OH + C{H_3}COOH $
Here, we can clearly see that one aldehyde changes into alcohol means reduction takes place and other one changes to acetic acid means oxidation takes place whereas trimethylacetaldehyde $ \left( {{{\left( {C{H_3}} \right)}_3}CCHO} \right) $ , benzaldehyde $ \left( {{C_6}{H_5}CHO} \right) $ , and formaldehyde $ \left( {HCHO} \right) $ does not contain any alpha hydrogen so they does not undergo Cannizaro reaction.
Therefore, option (B) is the correct option.

Note :
There is another name of this reaction and that name is a disproportionate reaction. As we see above in the Cannizaro reaction the product forms is acetic acid, it can also undergo Cannizaro reaction as it also contains three alpha hydrogens and when there is no alpha hydrogen present then these types of compounds undergo aldol condensation.