2-Chlorobutane on treatment with alcoholic KOH/`Delta` gives major product :

Options

A. 2-Butene
B. 1-Butene
C. 2-Butanol
D. 1-Butyne

Answer

To solve the problem of what major product is formed when 2-chlorobutane is treated with alcoholic KOH and heated, we can follow these steps:

### Step 1: Identify the Reactant
The reactant is 2-chlorobutane, which has the following structure:

```
CH3
|
CH3-CH-CH2-Cl
|
CH3
```

### Step 2: Understand the Reaction Conditions
The reaction is conducted in the presence of alcoholic KOH and heat. Alcoholic KOH is a strong base and promotes elimination reactions (E2 mechanism) rather than substitution reactions.

### Step 3: Mechanism of the Reaction
In the E2 elimination mechanism:
- The base (OH-) abstracts a proton (H) from a carbon adjacent to the carbon bearing the chlorine atom (the leaving group).
- The electrons from the C-H bond then form a double bond between the two carbons.
- The leaving group (Cl-) is expelled.

### Step 4: Identify the β-Hydrogens
For 2-chlorobutane, the β-hydrogens are on the carbons adjacent to the carbon that is bonded to chlorine. In this case, the β-hydrogens are on the CH2 and CH3 groups.

### Step 5: Choose the Most Accessible β-Hydrogen
The most accessible β-hydrogen for abstraction is the one on the CH2 group adjacent to the carbon with the Cl. The reaction will proceed as follows:

1. The base (OH-) abstracts a hydrogen from the CH2 group.
2. The electrons from the C-H bond form a double bond between the carbon bearing the Cl and the carbon that had the hydrogen removed.
3. The Cl leaves, resulting in the formation of a double bond.

### Step 6: Draw the Product
The product formed after the elimination will be:

```
CH3
|
CH3-C=CH2
```

This structure corresponds to but-2-ene.

### Step 7: Determine the Major Product
Since but-2-ene can exist in two isomeric forms (cis and trans), the trans isomer (trans-but-2-ene) is typically favored due to lower steric hindrance. However, both forms may be present, but the major product is generally considered to be the more stable one.

### Final Answer
The major product formed from the reaction of 2-chlorobutane with alcoholic KOH and heat is **but-2-ene**.

---