How does protic and aprotic solvents influence reaction mechanism considering SN1 vs SN2?
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1$\begingroup$ You will find your answer here and here $\endgroup$– William R. EbenezerCommented Apr 6, 2019 at 7:43
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As you know, $\mathrm{S_N1}$ and $\mathrm{S_N2}$ reactions have different mechanisms. $\mathrm{S_N1}$ occurs in 2 steps: formation of a carbocation and addition of the nucleophile. However, $\mathrm{S_N2}$ has a one-step mechanism where the addition of the nucleophile and the elimination of the leaving group happen simultaneously.
A protic solvent would participate in hydrogen bonding with the nucleophile since it can easily share one proton. A solvent shell is thus formed around the nucleophile, making him less able to undergo a $\mathrm{S_N2}$ reaction.
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$\begingroup$ I believe that a protic solvent also helps stabilise the carbocation in a Sn1 mechanism due to the dipole interactions. $\endgroup$ Commented Apr 6, 2019 at 13:40