Which of the following statements are correct ?

Options

A. The nucleophilic addition of `HCN` to (I) results in major addition to `(C = O)`.
B. The nucleophilic addition of `HCN` to `(I)` results in major addition `(C = C)`
C. The nucleophilic addition of `PhMgCl` to (II) results of 1,4-addition.
D. The nucleophilic addition of `PhMgCl` to (III) results in addition to `(C = C)`.

Explanation

To determine which statements regarding the nucleophilic addition to alpha-beta unsaturated carbonyl compounds are correct, we need to analyze the mechanisms involved in these reactions. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understanding the Structure
- **Identify the compound**: An alpha-beta unsaturated carbonyl compound has a carbonyl group (C=O) and a double bond (C=C) between the alpha and beta carbons.
- **Recognize the sites of nucleophilic attack**: The nucleophile can attack either the beta carbon (C=C) or the carbonyl carbon (C=O).

### Step 2: Analyzing Nucleophilic Attack
- **Case 1 - Attack on Carbonyl Carbon**: If the nucleophile attacks the carbonyl carbon, it leads to the formation of an intermediate that can undergo tautomerism, resulting in a product that is typically less stable.
- **Case 2 - Attack on Beta Carbon**: If the nucleophile attacks the beta carbon, it leads to a 1,4 addition product, which is generally more stable due to the formation of a new C-C bond.

### Step 3: Evaluating Bond Strength
- **Bond Strength Considerations**: The carbon-carbon double bond (C=C) is weaker than the carbon-oxygen double bond (C=O). Therefore, it is easier for the nucleophile to attack the beta carbon than the carbonyl carbon.
- **Conclusion on Major Product**: The 1,4 addition (attack on the beta carbon) is favored due to the weaker bond and the stability of the resulting product.

### Step 4: Analyzing the Statements
- **Statement A**: "In the nucleophilic addition of HCN to this compound, the major addition is to the CO bond."
- **Evaluation**: This is false. The major addition occurs at the C=C bond.

- **Statement B**: "The nucleophilic addition of HCN to the first compound results in the major addition to the C-C double bond."
- **Evaluation**: This is correct. The major product is formed from the attack on the beta carbon.

- **Statement C**: "The nucleophilic addition of phenyl magnesium chloride (PhMgCl) results in the 1,4 addition."
- **Evaluation**: This is correct. PhMgCl acts as a nucleophile and will favor 1,4 addition due to the reasons discussed.

- **Statement D**: "The nucleophilic addition of PhMgCl results in the addition to the C-C bond."
- **Evaluation**: This is also correct. Due to steric hindrance and bond strength, PhMgCl will predominantly add to the beta carbon.

### Final Conclusion
- **Correct Statements**: B, C, and D are correct.
- **Incorrect Statement**: A is incorrect.