Cannizaro reaction is not given by:

Question

Accepted Answer

Cannizaro reaction is a chemical reaction that involves the base-induced disproportionation of non-enolizable aldehydes to yield an alcohol and a carboxylic acid. This reaction typically occurs with aldehydes that do not have alpha-hydrogen atoms.

1. **Explanation for Option 4 (Ethanal):**
   - Ethanal (acetaldehyde) contains alpha-hydrogen atoms. This presence of alpha-hydrogens allows it to undergo aldol condensation rather than the Cannizaro reaction. In the presence of a base, ethanal can form an enolate ion, which is a key intermediate in the aldol condensation process. Therefore, ethanal does not participate in the Cannizaro reaction, making Option 4 the correct answer.

2. **Explanation for why other options are incorrect:**

- **Option 1 (1-Methyl cyclohexane carbaldehyde):**
     - This compound lacks alpha-hydrogen atoms due to the presence of a methyl group on the cyclohexane ring. Without alpha-hydrogens, it cannot form an enolate ion and is thus a suitable candidate for the Cannizaro reaction.

- **Option 2 (Benzaldehyde):**
     - Benzaldehyde does not have any alpha-hydrogen atoms because the aldehyde group is directly attached to the benzene ring. This absence of alpha-hydrogens makes benzaldehyde a classic example of a compound that undergoes the Cannizaro reaction.

- **Option 3 (Methanal):**
     - Methanal (formaldehyde) also lacks alpha-hydrogen atoms, as it is the simplest aldehyde with only hydrogen atoms attached to the carbonyl carbon. This makes it capable of undergoing the Cannizaro reaction.

In summary, ethanal is the only compound among the options that contains alpha-hydrogen atoms, allowing it to undergo aldol condensation instead of the Cannizaro reaction. This justifies why Option 4 is the correct answer.