Arrange decreasing order of reactivity of these compounds for nucleophilic substitution reaction.
(1) `CH_3-CH_2-O-underset(O)underset(||)overset(O)overset(||)S-CF_3`
(2) `CH_3-CH_2-O -TsCl`
(3) `CH_3-CH_2-Cl`
(4) `CH_3-CH_2-Br`
Select the correct answer from the codes given below

Options

A. 3,4,1,2
B. 3,4,2,1
C. 1,2,3,4
D. 1,2,4,3

Answer

To determine the decreasing order of reactivity of the given compounds for nucleophilic substitution reactions, we need to evaluate the effectiveness of their leaving groups. The better the leaving group, the more reactive the compound will be towards nucleophilic substitution.

### Step-by-Step Solution:

1. **Identify the Leaving Groups**:
- For compound (1) `CH_3-CH_2-O-underset(O)underset(||)overset(O)overset(||)S-CF_3`, the leaving group is `OSO2CF3`.
- For compound (2) `CH_3-CH_2-O -TsCl`, the leaving group is `OTs` (tosylate).
- For compound (3) `CH_3-CH_2-Cl`, the leaving group is `Cl` (chloride).
- For compound (4) `CH_3-CH_2-Br`, the leaving group is `Br` (bromide).

2. **Rank the Leaving Groups**:
- The order of leaving group ability is as follows:
- `OSO2CF3` (best leaving group)
- `OTs` (tosylate)
- `Br` (bromide)
- `Cl` (chloride)
- This means that `OSO2CF3` will leave the fastest, followed by `OTs`, then `Br`, and finally `Cl`.

3. **Determine the Reactivity Order**:
- Based on the leaving group ability, we can arrange the compounds in decreasing order of reactivity towards nucleophilic substitution:
- (1) `CH_3-CH_2-O-underset(O)underset(||)overset(O)overset(||)S-CF_3` (most reactive)
- (2) `CH_3-CH_2-O -TsCl`
- (4) `CH_3-CH_2-Br`
- (3) `CH_3-CH_2-Cl` (least reactive)

### Final Answer:
The decreasing order of reactivity of the compounds for nucleophilic substitution reactions is:
1. `CH_3-CH_2-O-underset(O)underset(||)overset(O)overset(||)S-CF_3`
2. `CH_3-CH_2-O -TsCl`
3. `CH_3-CH_2-Br`
4. `CH_3-CH_2-Cl`