Final answer:
Non-polar solvents favor unimolecular mechanisms such as SN1 and E1 due to less solvation of ions which stabilizes carbocation intermediates, unlike polar aprotic solvents which favor bimolecular mechanisms like SN2.
Step-by-step explanation:
Non-polar solvents typically favor unimolecular mechanisms in substitution and elimination reactions, such as the SN1 and E1 mechanisms respectively. Both SN1 and E1 mechanisms have a rate-determining step that involves the dissociation of the leaving group from a substrate to form a carbocation, which is a unimolecular process.
In an SN1 reaction, this leads to the substitution nucleophilic unimolecular mechanism, where the rate of the reaction is proportional to the substrate concentration.
Similarly, in an E1 reaction, the formation of the carbocation is followed by the elimination of a proton to form a double bond. Non-polar solvents do not adequately solvate ions, which helps to stabilize the carbocation intermediate, favoring these unimolecular processes over bimolecular processes such as SN2, which is favored by polar aprotic solvents.