Question

In the following groups,
$-OAc$, $-OMe$, $-OS{O}_2$$Me$, $-OS{O}_{2}C{F}_3$
I II III IV
The order of the leaving ability is:

• A. I > II > III > IV
• B. IV > III > I > II
• C. III > II > I > IV
• D. II > III > IV > I

Answer 1

Answer: (B)

IV > III > I > II

The weakest base is the best leaving group.

Basicity or nucleophilicity is inversely proportional to leaving a group.

i) $C{H}_{3}COOH\to C{H}_{3}CO{O}^{-}+H^{+}$
Weak acid strong base

ii) $MeOH\to Me{O}^{-}+H^{+}$

weakest acid strongest base

iii) $MeS{O}_{3}H\to MeS{O}_2{O}^{-}+H^{+}$
strong weak

iv) $C{F}_{3}S{O}_{3}H\to C{F}_{3}S{O}_3^{-}+H^{+}$
Acid Base
strongest weakest

Option B is correct.