- Which of the following compounds is most reactive under $\mathrm{S_N1}$ conditions?
- Arrange the following compounds in order of decreasing rate of $\mathrm{S_N1}$ hydrolysis:
A. II > III > IV > I
B. IV > III > II > I
C. III > IV > II > I
D. I > II > III > IV
Both these questions are based upon the rate of reactivity of $\mathrm{S_N1}$ reaction.
1) In this I thought the answer should be B because the rate of $\mathrm{S_N1}$ reaction depends on the ease of formation of carbocation. Being more electronegative, the electron density between carbon and chlorine bond is quite shifted towards chlorine, so it should be easier for chlorine to leave, hence forming the carbocation. Options A, B, and C allow the carbocation to be resonance stabilized so D cannot be the answer.
But the answer given is A.
Where am I wrong with this logic? I guess it might be because of more polarizing power of iodine, if it is this, then how are we supposed to figure out which one will be the dominating factor?
2) I think we check this on the basis of carbocation stability as well. Carbocation will be formed as $\ce{Br}$ leaves. Alkyl chain is electron releasing, so it must increase the electron density on the benzene ring which should be better for the stability of carbocation (as there is more electron density on the benzene ring to stabilize the positive charge). Hence the answer should be I > II > III > IV
But the answer is A.
Where am I wrong with my logic in both?