In Cannizzaro's reaction, which intermediate ion is best hydride `(H^(-))` ion donor ?

Options

A.
B.
C.
D.

Explanation

To solve the question regarding Cannizzaro's reaction and identify which intermediate ion is the best hydride ion donor, we can follow these steps:

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

### Step 2: Identify the Role of the Intermediate
In Cannizzaro's reaction, the intermediate that forms is a hydride ion donor. The hydride ion (H^(-)) is crucial because it is responsible for the reduction of one of the aldehyde molecules.

### Step 3: Consider the Effect of Electron-Withdrawing Groups
The presence of electron-withdrawing groups, such as the nitro group (NO2), enhances the ability of the molecule to donate a hydride ion. This is because electron-withdrawing groups stabilize the negative charge that develops when the hydride ion is released.

### Step 4: Analyze the Structure
In the context of the question, the structure of the intermediate that forms in the presence of a nitro group can be represented as follows:
- The aldehyde has a nitro group attached, which facilitates the release of the hydride ion.
- The structure can be visualized with the nitro group pulling electron density away, making it easier for the hydride ion to be released.

### Step 5: Identify the Best Hydride Ion Donor
Based on the analysis, the intermediate that has a nitro group (NO2) attached to it is the best hydride ion donor. The electron-withdrawing nature of the nitro group stabilizes the intermediate, allowing it to effectively donate the hydride ion.

### Conclusion
Thus, the correct answer is that the intermediate with the nitro group (NO2) is the best hydride ion donor in Cannizzaro's reaction.

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