The leaving group is that functional group which is ejected with `overline e^, s` of the `sigma` -bond in a reaction. Better the leaving group, faster is the reaction. The relative leaving ability of the leaving group `X` in `(R - X)` is increased by :
(i) The polarisability of `(R - X)` bond.
(ii) The stability of `X^(Ө)`.
(iii) The degree of stabilisation through solvation of `X`.
(iv) The strength of `(R - X)` bond.
The leaving group tendency is also called fugacity.
Which one of the followingd has the highest fugacity ?

Options

A. Tosylate `(overset (Ө) O Ts)`
B. Mesylate
C. Triflate `(F_3 C - SO_3^(Ө))`
D. All are equal

Explanation

To determine which leaving group has the highest fugacity, we need to analyze the leaving groups provided: tosylate, mesylate, and triflate. The fugacity of a leaving group is related to its ability to stabilize the negative charge after it leaves, which is influenced by the acidity of the corresponding acid.

### Step-by-Step Solution:

1. **Identify the Leaving Groups**:
- We have three leaving groups: tosylate (OTs), mesylate (OMs), and triflate (OTf).

2. **Write the Corresponding Acids**:
- Tosylate: The corresponding acid is p-toluenesulfonic acid (HOTS).
- Mesylate: The corresponding acid is methanesulfonic acid (HCH3SO3).
- Triflate: The corresponding acid is trifluoromethanesulfonic acid (HCF3SO3).

3. **Determine the Acidity of Each Acid**:
- The strength of an acid is inversely related to the strength of its conjugate base. A stronger acid has a weaker conjugate base.
- The order of acidity is as follows:
- Trifluoromethanesulfonic acid (HCF3SO3) > Methanesulfonic acid (HCH3SO3) > p-Toluenesulfonic acid (HOTS).

4. **Determine the Basicity of the Conjugate Bases**:
- The conjugate bases of these acids are:
- Triflate: CF3SO3^-
- Mesylate: CH3SO3^-
- Tosylate: C6H5SO3^- (p-toluenesulfonate)
- The basicity order (and thus the leaving group ability) is the reverse of the acidity order:
- CF3SO3^- (triflate) < CH3SO3^- (mesylate) < C6H5SO3^- (tosylate).

5. **Conclusion**:
- Since triflate has the weakest conjugate base (CF3SO3^-), it is the most stable and thus has the highest fugacity among the three leaving groups.

### Final Answer:
The leaving group with the highest fugacity is **triflate (OTf)**.

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