Question

The correct order of the following compounds showing increasing tendency towards nucleophilic substitution reaction is:

• A. (iv) < (i) < (iii) < (ii)
• B. (iv) < (i) < (ii) < (iii)
• C. (i) < (ii) < (iii) < (iv)
• D. (iv) < (iii) < (ii) < (i)

Answer 1

The correct option is C

(i) < (ii) < (iii) < (iv)

The correct option is (C):

Explanation for the correct answer:

Nucleophilic substitution reaction:-

1. It is basically a chemical reaction and in this reaction, an electron rich nucleophile will attack the positively charged electrophile and will replace with a leaving group.
2. For the nucleophilic substitution reaction to take place, there must be a low temperature and a dilute aqueous solution of the strong base.
3. Mesomeric effect or the M effect is basically defined as the polarity produced in a molecule or in a conjugated system by basically the movement of the $\mathrm{\pi }$ electrons towards or away from the substituent group.
4. This Mesomeric effect is negative when the substituent is an electron withdrawing group whereas the Mesomeric effect is positive when the substituent group is an electron releasing group.
5. Similarly the Inductive or I effect is basically the polarization of the sigma bond when an electronegative atom or the group withdraws the electron pair of the sigma bond towards itself.
6. Basically the electron withdrawing nature of the group or atoms is called the negative inductive effect that is -I , whereas the groups that are attached to a molecule and increases the overall electron density on the molecule and so the molecule is also able to donate the electrons which will further make it basic refers to as the +I effect
7. So basically, $\mathrm{Rate}\mathrm{of}\mathrm{substitution}\mathrm{reaction}\propto \mathrm{stability}\mathrm{of}\mathrm{carbocation}$
8. Also the $\mathrm{Reactivity}\propto –\mathrm{M}\mathrm{group}\mathrm{present}\mathrm{at}\mathrm{o}/\mathrm{p}\mathrm{position}.$

Therefore, the correct option is (C):- (i) < (ii) < (iii) < (iv).