Cannizaro's reaction is not given by ________

Options

A.
B.
C. `HCHO`
D. `CH_3CHO`

Explanation

To determine which compound does not undergo Cannizzaro's reaction, we need to analyze the options based on the presence of alpha hydrogen atoms. Cannizzaro's reaction occurs with aldehydes that lack alpha hydrogens. Here’s a step-by-step solution:

### Step 1: Understand Cannizzaro's Reaction
Cannizzaro's reaction is a redox reaction that occurs in aldehydes that do not have alpha hydrogen atoms. In this reaction, one molecule of the aldehyde is oxidized to a carboxylic acid, while another molecule is reduced to an alcohol.

### Step 2: Analyze Each Option
We will analyze each option to check for the presence of alpha hydrogen atoms.

#### Option A: Aldehyde with a six-membered ring (e.g., cyclohexanecarbaldehyde)
- Structure: CHO (aldehyde) attached to a six-membered ring.
- Alpha Carbon: The carbon next to the aldehyde carbon is part of the ring and has no hydrogen atoms.
- Conclusion: No alpha hydrogen present; this compound can undergo Cannizzaro's reaction.

#### Option B: Aldehyde with a carbon chain (e.g., 2-methylbutanal)
- Structure: CH3-CHO (aldehyde) with a carbon chain.
- Alpha Carbon: The carbon next to the aldehyde carbon has three hydrogen atoms.
- Conclusion: Alpha hydrogen present; this compound cannot undergo Cannizzaro's reaction.

#### Option C: Aldehyde with no alpha carbon (e.g., formaldehyde)
- Structure: HCHO (formaldehyde).
- Alpha Carbon: There is no carbon adjacent to the aldehyde carbon.
- Conclusion: No alpha hydrogen present; this compound can undergo Cannizzaro's reaction.

#### Option D: Acetaldehyde (ethanal)
- Structure: CH3CHO.
- Alpha Carbon: The carbon next to the aldehyde has three hydrogen atoms.
- Conclusion: Alpha hydrogen present; this compound cannot undergo Cannizzaro's reaction.

### Step 3: Identify the Correct Answer
Based on the analysis:
- The compound that does not undergo Cannizzaro's reaction is **Option B** (the aldehyde with a carbon chain that has alpha hydrogen).

### Final Answer
**Cannizzaro's reaction is not given by Option B.**