Which of the following reactions will give the major and minor products?
`CH_3-CH_2underset(Br)underset(|)(CH)-CH_3underset("heat")overset(alc. KOH)toCH_3-underset((A))(CH=CH)+underset((B))(CH_3-CH_2-CH=CH_2)`

Options

A. (A) is major product and (B) is minor product.
B. (A) is minor product and (B) is major product.
C. Both (A) and (B) are major products.
D. Only (B) is formed and (A) is not formed.

Explanation

To determine the major and minor products of the reaction of 2-bromobutane with alcoholic KOH, we can follow these steps:

### Step 1: Identify the Reactant
The reactant is 2-bromobutane, which has the following structure:
\[ CH_3-CH_2-CH(Br)-CH_3 \]

### Step 2: Understand the Reaction Conditions
The reaction is carried out in the presence of alcoholic KOH. Alcoholic KOH acts as a strong base and promotes elimination reactions (dehydrohalogenation) rather than substitution reactions.

### Step 3: Determine the Mechanism
In this reaction, the base (KOH) will abstract a beta-hydrogen (a hydrogen atom from the carbon adjacent to the carbon bearing the bromine atom). This results in the elimination of HBr and the formation of a double bond.

### Step 4: Identify Beta-Hydrogens
For 2-bromobutane:
- The beta-carbons are the ones adjacent to the carbon with the bromine.
- The beta-hydrogens that can be removed are located on the carbons adjacent to the carbon with the Br.

### Step 5: Possible Products
1. **Elimination of a beta-hydrogen from the carbon with two methyl groups (C1)** leads to:
- **But-2-ene** (more substituted alkene)
- Structure: \( CH_3-CH=CH-CH_3 \)

2. **Elimination of a beta-hydrogen from the carbon with one methyl group (C2)** leads to:
- **But-1-ene** (less substituted alkene)
- Structure: \( CH_3-CH_2-CH=CH_2 \)

### Step 6: Determine Major and Minor Products
According to Zaitsev's rule (or Saytzeff's rule), the more substituted alkene is favored as the major product. In this case:
- **But-2-ene** (product A) is more substituted (it has two alkyl groups attached to the double bond).
- **But-1-ene** (product B) is less substituted (it has only one alkyl group attached to the double bond).

### Conclusion
- **Major Product (A)**: But-2-ene
- **Minor Product (B)**: But-1-ene

### Final Answer
The major product is but-2-ene (A) and the minor product is but-1-ene (B).

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