Substrate structure controls substitution mechanism S_N1 or S_N2

Load the structures and click either S_N1 or S_N2 to find out the correct answer

The most important factor in determining which mechanism (S_N1 or S_N2) applies to an organic compound is the structure of the carbon skeleton. Most compounds that can form relatively stable cations generally do so and react via the S_N1 mechanism, while the others have to react via the S_N2 mechanism.

Cations are more stable if they are heavily substituted, but this is bad for an S_N2 reaction because the nucleophile would have to thread its way into the carbon atom through the alkyl groups.

Which mechanism (S_N1 or S_N2) will the following compounds favour?

Think about the stabilizing effect alkyl groups can have, and also their role in terms of steric hindrance.

D. H. Aue, Wiley Interdiscip. Rev. Comput. Mol. Sci., 2011, 1, 487–508.