The correct increasing order of reactivity for following alkyl halides towards elimination reaction with alcoholic KOH is :
(I)`CH_3-undersetunderset(Cl)(|)CH-CH_3 " " (II)CH_3-undersetunderset(Br)(|)oversetoverset(CH_3)(|)C-CH_2CH_3 " " (III)CH_3-undersetunderset(Cl)(|)oversetoverset(CH_3)(|)C-CH_2CH_3`

Options

A. II gt I gt III
B. I gt II gt III
C. II gt III gt I
D. III gt II gt I

Answer

To determine the correct increasing order of reactivity for the given alkyl halides towards elimination reactions with alcoholic KOH, we need to analyze the structures and the factors affecting their reactivity.

### Step 1: Identify the Structures
We have three alkyl halides:
1. (I) CH₃-CH(Cl)-CH₃
2. (II) CH₃-C(CH₃)(Br)-CH₂-CH₃
3. (III) CH₃-C(Cl)-CH₂-CH₃

### Step 2: Determine the Type of Alkyl Halides
- **(I)** is a secondary alkyl halide (1 Cl on a secondary carbon).
- **(II)** is a tertiary alkyl halide (1 Br on a tertiary carbon).
- **(III)** is also a secondary alkyl halide (1 Cl on a secondary carbon).

### Step 3: Analyze the Elimination Reaction
In elimination reactions, the stability of the resulting alkene is crucial. The more substituted the alkene, the more stable it is, which typically leads to a higher reactivity of the alkyl halide.

### Step 4: Count the Beta Carbons
- **(I)** has 2 beta carbons.
- **(II)** has 3 beta carbons.
- **(III)** has 3 beta carbons.

### Step 5: Consider the Leaving Group Ability
The ability of the leaving group also plays a significant role in the reactivity of alkyl halides:
- The order of leaving group ability is: I > Br > Cl.
Thus, Br (in II) is a better leaving group than Cl (in I and III).

### Step 6: Compare Reactivities
- **(I)**: Secondary alkyl halide with Cl (2 beta carbons).
- **(II)**: Tertiary alkyl halide with Br (3 beta carbons, better leaving group).
- **(III)**: Secondary alkyl halide with Cl (3 beta carbons).

### Conclusion
Given that (II) has a better leaving group (Br) and more beta carbons, it will be the most reactive. (III) and (I) both have Cl as the leaving group, but (III) has more beta carbons than (I), making it more reactive than (I).

### Final Order of Reactivity
The increasing order of reactivity towards elimination with alcoholic KOH is:
**(I) < (III) < (II)**