The order of leaving group ability is
`.^(-)underset((I))(OAc).^(-) underset((II))(OMe).^(-)underset((III))(SO_3Me).^(-)underset((IV))(SO_3CF_3)` The order of leaving group ability is

Options

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

Answer

To determine the order of leaving group ability among the given groups, we need to analyze the stability of the leaving groups after they depart. The more stable the leaving group is after it leaves, the better it is as a leaving group.

### Step-by-Step Solution:

1. **Identify the Leaving Groups**:
The groups we are comparing are:
- (I) OAc⁻ (Acetate)
- (II) OMe⁻ (Methoxide)
- (III) SO₃Me⁻ (Methanesulfonate)
- (IV) SO₃CF₃⁻ (Trifluoromethanesulfonate)

2. **Analyze the Stability of Each Leaving Group**:
- **(IV) SO₃CF₃⁻**: The trifluoromethyl group (CF₃) is highly electronegative and can stabilize the negative charge through inductive effects. Thus, this group is very stable after leaving.
- **(III) SO₃Me⁻**: The methyl group (Me) is less electronegative than CF₃, but the sulfonate group (SO₃) still provides good stabilization of the negative charge. Therefore, it is a good leaving group, but not as good as SO₃CF₃.
- **(I) OAc⁻**: The acetate ion can stabilize the negative charge through resonance, but it is less stable than the sulfonate groups due to the lack of strong electron-withdrawing groups.
- **(II) OMe⁻**: The methoxide ion is the least stable of the four because the negative charge is localized on the oxygen without significant resonance or inductive stabilization from electronegative groups.

3. **Rank the Leaving Groups**:
Based on the stability of the leaving groups after they leave, we can rank them:
- (IV) SO₃CF₃⁻ > (III) SO₃Me⁻ > (I) OAc⁻ > (II) OMe⁻

4. **Final Order of Leaving Group Ability**:
The order of leaving group ability is:
- SO₃CF₃⁻ > SO₃Me⁻ > OAc⁻ > OMe⁻

### Conclusion:
The correct order of leaving group ability is:
**(IV) > (III) > (I) > (II)**