The key step in cannizzaro's reaction is the intermolecular shift of

Options

A. Proton
B. Hydride ion
C. Hydronium ion
D. Methyl group

Answer

**Step-by-Step Solution:**

1. **Understanding Cannizzaro's Reaction**: Cannizzaro's reaction is a redox reaction that occurs in aldehydes lacking alpha-hydrogens. The reaction involves the disproportionation of aldehydes in the presence of a strong base.

2. **Identifying the Reactant**: The key requirement for Cannizzaro's reaction is that the aldehyde must have no alpha-hydrogens. For example, benzaldehyde (C6H5CHO) is a suitable reactant because it has no alpha-hydrogens.

3. **Formation of Alkoxide Ion**: When benzaldehyde reacts with a strong base (like sodium hydroxide), the hydroxide ion (OH-) acts as a nucleophile and attacks the carbonyl carbon of the aldehyde. This leads to the formation of an alkoxide ion (C6H5CH(OH)O-).

4. **Hydride Transfer**: The key step in Cannizzaro's reaction is the intermolecular shift of a hydride ion (H-). The alkoxide ion formed can transfer a hydride ion to another molecule of aldehyde. This process leads to the formation of an alcohol and a carboxylic acid.

5. **Formation of Products**: After the hydride transfer, one molecule of the aldehyde is reduced to an alcohol (C6H5CH2OH - benzyl alcohol), while the other molecule is oxidized to a carboxylic acid (C6H5COOH - benzoic acid).

6. **Final Reaction**: The overall reaction can be summarized as:
\[ 2 \text{C}_6\text{H}_5\text{CHO} + \text{OH}^- \rightarrow \text{C}_6\text{H}_5\text{CH}_2\text{OH} + \text{C}_6\text{H}_5\text{COO}^- \]