Arrange the following compounds in order of their reactivity towards `S_N2` reaction
`(i) CH_3(CH_2)_(2)CH_2Cl`
(ii) `(CH_3)_(2)CHCH_2CH_2Cl`
(iii) `CH_3CH_2-overset(CH_3)overset(CH_3)overset(|)(CH)-CH_2Cl`
(iv) `CH_3-underset(CH_3)underset(|)overset(CH_3)overset(|)(C )-CH_2Cl`

Options

A. (iv) gt (ii) gt (i) gt (iii)
B. (ii) gt (iii)gt (iv) gt (i)
C. (iii) gt (i) gt (ii) gt (iv)
D. (i) gt (ii) gt (iii) gt (iv)

Answer

To determine the order of reactivity of the given compounds towards the \( S_N2 \) reaction, we need to analyze the structure of each compound and assess their steric hindrance. The \( S_N2 \) mechanism favors primary alkyl halides over secondary and tertiary due to less steric hindrance.

### Step-by-Step Solution:

1. **Identify the Structures of the Compounds**:
- (i) \( CH_3(CH_2)_2CH_2Cl \) - This is a primary alkyl halide.
- (ii) \( (CH_3)_2CHCH_2CH_2Cl \) - This is a secondary alkyl halide.
- (iii) \( CH_3CH_2C(CH_3)(CH_2)Cl \) - This is also a secondary alkyl halide.
- (iv) \( CH_3C(CH_3)(CH_3)CH_2Cl \) - This is a tertiary alkyl halide.

2. **Determine the Type of Each Alkyl Halide**:
- (i) Primary: \( CH_3(CH_2)_2CH_2Cl \)
- (ii) Secondary: \( (CH_3)_2CHCH_2CH_2Cl \)
- (iii) Secondary: \( CH_3CH_2C(CH_3)(CH_2)Cl \)
- (iv) Tertiary: \( CH_3C(CH_3)(CH_3)CH_2Cl \)

3. **Assess Reactivity Based on Steric Hindrance**:
- \( S_N2 \) reactions are favored by less steric hindrance. Therefore, the order of reactivity will be:
- Primary alkyl halides react the fastest.
- Secondary alkyl halides react slower than primary but faster than tertiary.
- Tertiary alkyl halides react the slowest due to steric hindrance.

4. **Rank the Compounds**:
- (i) \( CH_3(CH_2)_2CH_2Cl \) - Most reactive (Primary)
- (ii) \( (CH_3)_2CHCH_2CH_2Cl \) - Second most reactive (Secondary)
- (iii) \( CH_3CH_2C(CH_3)(CH_2)Cl \) - Third most reactive (Secondary)
- (iv) \( CH_3C(CH_3)(CH_3)CH_2Cl \) - Least reactive (Tertiary)

5. **Final Order of Reactivity**:
- The order of reactivity towards \( S_N2 \) is:
- (i) > (ii) > (iii) > (iv)

### Final Answer:
The order of reactivity towards \( S_N2 \) is:
1. \( CH_3(CH_2)_2CH_2Cl \) (i)
2. \( (CH_3)_2CHCH_2CH_2Cl \) (ii)
3. \( CH_3CH_2C(CH_3)(CH_2)Cl \) (iii)
4. \( CH_3C(CH_3)(CH_3)CH_2Cl \) (iv)