Question

most of the Sn1 reactions don't proceed with complete racemisation. explain

Answer 1

Although it’s often said that the SN1 proceeds with “racemization” of stereocenters, in practice a 50/50 split of stereocenters may not be obtained due to “ion pairing” effects. In other words, the leaving group could leave, but not fully dissociate from the vicinity of the carbocation, which could block a nucleophile from attacking the nucleophile from that face. For that reason it’s a little bit more correct to say that it proceeds with a “mixture of retention and inversion” rather than “racemization”.