In the following groups:
1. –OAc         2. –OMe          3. –OSO₂Me          4. –OSO₂CF₃
the order of leaving group ability is

4 > 3 > 1 > 2

The correct answer is option 2. 4 > 3 > 1 > 2.

Let us delve into the explanation of why the leaving group ability varies among the groups provided: \(–OAc, –OMe, –OSO_2Me\), and \(–OSOCF_3\).

4. \(–OSOCF_3\) (Trifluoromethanesulfonoxy Group)

The trifluoromethanesulfonoxy group has a sulfonyl group \((–SO_\) bonded to a trifluoromethyl group \((–CF_3)\).  The trifluoromethyl group is highly electron-withdrawing due to the strong inductive effect of the fluorine atoms. This substantial electron-withdrawing effect pulls electron density away from the sulfonyl group, which enhances the stabilization of the negative charge on the leaving oxygen atom. The strong electron-withdrawing nature of \(–CF_3\) makes this an excellent leaving group because it stabilizes the negative charge effectively after the group departs.

3. \(OSO_2Me\) (Methanesulfonoxy Group

The methanesulfonoxy group consists of a sulfonyl group \((–SO_2)\) bonded to a methoxy group \((–OCH_3)\). The sulfonyl group \((–SO_2)\) is an electron-withdrawing group, which helps stabilize the negative charge on the oxygen. However, the methoxy group (–OCH₃) is less electron-withdrawing compared to the trifluoromethyl group. The methoxy group has a slight electron-donating effect due to its oxygen atom, but the sulfonyl group still provides substantial stabilization. Although it is a good leaving group due to the sulfonyl group’s stabilization, it is not as effective as the trifluoromethanesulfonoxy group because the methoxy group does not contribute as strongly to electron-withdrawing effects.

1. \(–OAc\) (Acetoxy Group)

The acetoxy group has an ester structure \(–OCOCH_3\). The acetoxy group can stabilize the negative charge through resonance. The resonance between the carbonyl group and the oxygen helps distribute the negative charge, but this stabilization is not as strong as that provided by sulfonyl groups. The acetoxy group is a reasonable leaving group due to resonance stabilization but is less effective compared to sulfonyl groups which have stronger electron-withdrawing effects.

2.. \(–OMe\) (Methoxy Group)

The methoxy group is \(–OCH_3\). The methoxy group is relatively poor at stabilizing the negative charge because it is a weak electron donor rather than a strong electron-withdrawing group. Its inductive effects are minimal, and it does not effectively stabilize the negative charge left behind after departure: This group is the weakest leaving group among those listed due to its inability to stabilize the negative charge effectively.

Summary

The effectiveness of a leaving group is determined by how well it can stabilize the negative charge once it has left the molecule. Strong electron-withdrawing groups enhance this stabilization, making the leaving group better. The trifluoromethanesulfonoxy group \((–OSO_2CF_3)\) is the most effective due to the strong electron-withdrawing effect of the trifluoromethyl group. The methanesulfonoxy group \((–OSO_2Me)\) is also effective but not as much as the trifluoromethanesulfonoxy group. The acetoxy group \((–OAc)\) is less effective, and the methoxy group \((–OMe)\) is the least effective due to its weak electron-withdrawing properties.

Thus, the correct order of leaving group ability is: 4 > 3 > 1 > 2