Strength of nucleophiles among SN1 and SN2 reactions As per the theory of chemistry, we say that unstable carbocations undergo SN2 reactions as it involves strong nucleophile. As a consequence, it does not lead to the formation of reaction intermediate, i.e. a carbocation.
Similarly, in stable carbocations undergo SN1 reaction by substitution of a weak nucleophile.
Why necessarily weak nucleophiles are involved? In case of SN2, since the carbocation is unstable, a strong nucleophile which prevents the formation of carbocation. But in SN1, since stable carbocation is involved, why shouldn't both strong and weak nucleophiles be involved?
This seems to be true only because SN1 reactions prefer polar protic solvents which stabilize both the leaving group and the carbocation. But such solvents also surround strong nucleophile and hinder it from the carbocation.
Weak nucleophiles on the other hand don't interact with protic solvents as much and thus stand a better chance of getting close to carbocation.