Which of the following statements are correct about the addition of `HBr` to buta-1,3-diene ?

Options

A. 1,2-Addition product , 3-bromobut-1-ene) is the major product at lower temperature `(-80^@C)` and is a kinetic control or rate-controlled product.
B. 1,4-Addition product , 1-bromobut-2-ene) is the major product at high temperature `(40^@ C)` and is a thermodynamic or equilibrium-controlled product.
C. In a non-polar solvent (e.g., hexane), 1,2-addition product is predominantly favoured.
D. In a polar solvent (e.g., acetic acid) 1,4-addition product is predominatly favoured.

Answer

To analyze the addition of HBr to buta-1,3-diene, we will break down the process into several steps and evaluate the statements provided.

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant is buta-1,3-diene, which has the structure CH2=CH-CH=CH2.

2. **Addition of HBr**:
- When HBr is added to buta-1,3-diene, the reaction proceeds through the formation of a carbocation intermediate. The H from HBr adds to one of the double-bonded carbons, leading to the formation of a carbocation.

3. **Formation of Carbocation**:
- The addition of H to the first carbon (C1) results in a secondary carbocation at C2 (CH2=CH-CH^+-CH2), which is more stable than a primary carbocation that could form if H added to C2.

4. **Resonance Stabilization**:
- The carbocation can undergo resonance. The positive charge can be delocalized, increasing the stability of the intermediate. This resonance allows the carbocation to stabilize further, favoring the formation of the 1,2 addition product.

5. **Kinetic vs. Thermodynamic Control**:
- At low temperatures, the more stable (kinetically favored) product is formed, which is the 1,2 addition product (where H adds to C1 and Br adds to C2).
- At high temperatures, the less stable (thermodynamically favored) product is formed, which is the 1,4 addition product (where H adds to C1 and Br adds to C4).

6. **Effect of Solvent**:
- In a nonpolar solvent (like hexane), the addition of HBr is not hindered, allowing the more stable 1,2 addition product to be favored.
- In a polar solvent, HBr is less free to react due to hydrogen bonding, leading to the formation of the less stable 1,4 addition product.

### Evaluation of Statements:
- **Statement A**: "1,2 addition product is the major product at low temperature and it is kinetically controlled or rate controlled product."
- **Correct**: This aligns with our understanding of kinetic control.

- **Statement B**: "1,4 addition product is the major product at high temperature and thermodynamically or equilibrium control product."
- **Correct**: This is consistent with thermodynamic control.

- **Statement C**: "In a nonpolar solvent (for example, hexane), 1,2 addition product is predominantly favored."
- **Correct**: Nonpolar solvents favor the formation of the more stable product.

- **Statement D**: "In a polar solvent, 1,4 addition product is predominantly favored."
- **Correct**: Polar solvents hinder the reaction, leading to the formation of the less stable product.

### Conclusion:
All statements (A, B, C, D) are correct regarding the addition of HBr to buta-1,3-diene.