Question

Rank the following in decreasing order of leaving group ability. 

Answer 1

The answer will be B (I > III > II > IV)

this is due to that the leaving group ability of any group depends on the stability of that anion. so by this we can infer that stronger the acid corresponding to the anion the better is the leaving group.

In structure I , the anion is stablest one due to delocalisation of the negative charge and also the corresponding acid is strong.

In structure II, HCl is a much strong acid but due to no extra stabilisation of the negative charge it comes second.

In structure III, the corresponding acid CH3COOH is weak but stronger than H2O

In structure IV, corresponding acid H2O is a very weak so OH- is not stable so it is a bad leaving group.