Which of the following statements are correct about the bisulphite addition product of a carbonyl compound ?

Options

A. The nucleophile is `HSO_(3)^(Θ)`.
B. The nucleophile is `SO_(3)^(2-)`.
C. The `(C-S)` bond is formed rather than `(C-O)` bond because O is more nucleophilic than S.
D. The bisulphite adduct can be regenerated to carbonyl compound by both acid base.

Answer

To determine which statements are correct about the bisulfite addition product of a carbonyl compound, we need to analyze the reaction mechanism and the properties of the involved species. Here’s a step-by-step solution:

### Step 1: Understand the Reactants
The bisulfite addition product involves sodium bisulfite (NaHSO3), which contains the bisulfite ion (HSO3^-). The bisulfite ion acts as a nucleophile and can react with carbonyl compounds (aldehydes and ketones).

**Hint:** Identify the nucleophile in the reaction and its structure.

### Step 2: Identify the Nucleophile
In the bisulfite addition reaction, the nucleophile is the sulfur atom in the bisulfite ion (HSO3^-). Although oxygen atoms are present, they are involved in resonance and do not act as nucleophiles in this reaction. The sulfur atom has a lone pair of electrons that can attack the electrophilic carbon of the carbonyl group.

**Hint:** Focus on the role of sulfur as a nucleophile compared to oxygen.

### Step 3: Mechanism of the Reaction
When the bisulfite ion attacks the carbonyl carbon, a new bond is formed between the sulfur atom and the carbon atom. The oxygen of the carbonyl group becomes negatively charged. The resulting product is a sulfonic acid derivative, which can be represented as R2C(OH)(SO3H).

**Hint:** Visualize the reaction mechanism to understand how the nucleophile interacts with the carbonyl compound.

### Step 4: Analyze the Statements
Now, let’s evaluate the given statements:

- **Statement A:** The nucleophile is HSO3^-.
- **Evaluation:** This statement is incorrect because the nucleophile is the sulfur atom in the bisulfite ion, not the entire ion itself.

- **Statement B:** The nucleophile is sulfite ion.
- **Evaluation:** This statement is correct. The sulfite ion (SO3^2-) can act as a nucleophile, but in the context of bisulfite addition, it is the bisulfite ion (HSO3^-) that is primarily involved.

- **Statement C:** A carbon-sulfur bond is formed rather than a carbon-oxygen bond because O is more nucleophilic than S.
- **Evaluation:** This statement is incorrect. A carbon-sulfur bond is indeed formed, but the reason given is wrong. Sulfur is a better nucleophile than oxygen due to its larger size and availability of lone pair electrons.

- **Statement D:** The bisulfite adduct can be regenerated to the carbonyl compound by both acid and base.
- **Evaluation:** This statement is correct. The bisulfite adduct can be hydrolyzed back to the carbonyl compound in both acidic and basic conditions.

### Conclusion
The correct statements about the bisulfite addition product of a carbonyl compound are **B and D**.

**Final Answer:** The correct statements are B and D.

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