Mark the correct increasing order of reactivity of the following compounds with .
(i) a < b < c
(ii) b < a < c
(iii) b < c < a
(iv) c < b < a
The answer is the option (iii). The type of reaction taking place in this process is the nucleophilic substitution reaction. The mechanism followed is , so the first slow step of the mechanism involves the formation of carbocation that determines the rate of reaction and then the addition of a nucleophile. The carbocation formed also controls the reactivity of this product formed. But in case of the presence of a highly electron-withdrawing group , the carbocation will be destabilised, and the reaction will not be favoured.
Whereas the high electron-withdrawing nature of the group due to lone pair presence, its tendency of electron-withdrawing is slightly low than , it will also manage to destabilise the carbocation and do not favour the reaction.
In the case of the first compound, , the absence of any destabilising factors makes the reaction occurrence favourable. Thus, the concluded increasing order of reactivity will be Option (iii) b < c < a