Which of the following statements is/are correct for alkyl halide ?

Options

A. In most unimolecular reactions of alkyl halide `S_N1` reactions is favoured over E1 reaction
B. E1 mechanism is favoured as compared to `S_N1` mechanism by branching at `beta` carbon.
C. In unimolecular reaction, increasing the temperature favours E1 mechanism
D. E1 reactions are favoured by the use of weak bases and by the use of polar solvents.

Explanation

To determine which statements are correct regarding alkyl halides, let's analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement 1**: In most unimolecular reactions of alkyl halides, SN1 reaction is favored over E1 reaction.

**Explanation**: This statement is true. In unimolecular reactions, particularly at low temperatures, the SN1 mechanism is favored because it involves the formation of a carbocation intermediate. At lower temperatures, the entropy change is less favorable for elimination reactions (E1), making SN1 more favorable.

### Step 2: Analyze the second statement
**Statement 2**: E1 mechanism is favored as compared to SN1 mechanism by branching due to more steric hindrance.

**Explanation**: This statement is false. Increased branching in alkyl halides leads to more steric hindrance, which actually favors the SN1 mechanism over the E1 mechanism. In sterically hindered substrates, the formation of a carbocation is favored, while elimination (E1) becomes less favorable due to the difficulty in accessing the β-hydrogens.

### Step 3: Analyze the third statement
**Statement 3**: In unimolecular reactions, increasing the temperature favors the E1 mechanism.

**Explanation**: This statement is true. As temperature increases, the entropy change (ΔS) becomes more favorable for elimination reactions (E1). Higher temperatures provide the energy needed for the elimination process to occur, making E1 more favorable compared to SN1.

### Step 4: Analyze the fourth statement
**Statement 4**: E1 mechanism is favored by the use of weak bases and polar solvents.

**Explanation**: This statement is true. The E1 mechanism involves the formation of a carbocation, which can be stabilized by polar solvents. Weak bases are also effective in facilitating the elimination process by easily removing a proton from the carbocation, leading to the formation of an alkene.

### Conclusion
After analyzing all the statements:
- **Statement 1**: True
- **Statement 2**: False
- **Statement 3**: True
- **Statement 4**: True

Thus, the correct statements regarding alkyl halides are Statements 1, 3, and 4.