Benzaldehyde reacts with alcoholic KCN to give :

Options

A. `C_(6)H_(5)CHOHCN`
B. `C_(6)H_(5)CHOHCOC_(6)H_(5)`
C. `C_(6)H_(5)CHOHCOOH`
D. `C_(6)H_(5)CHOHCHOCH_(6)H_(5)`

Explanation

To solve the question regarding the reaction of benzaldehyde with alcoholic KCN, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant is benzaldehyde (C6H5CHO), which contains a carbonyl group (C=O) and does not have an alpha hydrogen.

2. **Understand the Role of KCN**:
- KCN in alcoholic solution acts as a nucleophile. The cyanide ion (CN-) can attack the carbonyl carbon of benzaldehyde.

3. **Mechanism of Reaction**:
- When benzaldehyde reacts with KCN, the nucleophilic cyanide ion attacks the electrophilic carbon of the carbonyl group, leading to the formation of a cyanohydrin intermediate.

4. **Formation of Benzoin**:
- In the presence of another molecule of benzaldehyde, the cyanohydrin can undergo a condensation reaction. The hydroxyl group from the cyanohydrin can attack another benzaldehyde molecule, leading to the formation of benzoin (C6H5-CHOH-C(=O)-C6H5).

5. **Final Product**:
- The final product of this reaction is benzoin, which is a hydroxy ketone. Its structure can be represented as:
- C6H5-CHOH-C(=O)-C6H5.

6. **Chirality of Benzoin**:
- Benzoin is chiral and exists as a pair of enantiomers (R and S forms).

7. **Condensed Formula**:
- The condensed formula of benzoin is C6H5(OH)C(=O)C6H5, which matches with the options provided in the question.

8. **Conclusion**:
- The correct answer is benzoin, which corresponds to option B.