How can I determine SN2 or SN1?

1 Answer
Shulgin · Stefan V.
Apr 18, 2018

There are many things you can look at to determine if a reaction is #S_N1# or #S_N2#.

Explanation:

The first thing you can look after is how large the substrate is. If we have a leaving group on a tertiary carbon atom the reaction would most likely be an #S_N1# reaction because of steric hindrance. If the leaving group sits on a methyl group it would most likely be an #S_N2# reaction.

Examples of these would be:

#S_N1# reaction:

https://www.masterorganicchemistry.com
Here you can see that the leaving group #(Br)# is sitting on a tertiary carbon.

#S_N2# reaction:

https://www.masterorganicchemistry.com
Here you can see that the leaving group #(Br)# is sitting on a methyl group.

Of course, this is not always the case (depending on solvent and nucleophile). The biggest indicator might be the nucleophile and the solvent.

In an #S_N1# reaction, the nucleophile is a neutral (#H_2O# or #R"−"OH#) with a polar protic solvent (e.g. alcohols). In an #S_N2# reaction, the nucleophile is negatively charged (#O^−#, #CN^−# ...) with a polar aprotic solvent (e.g. DMSO, acetone).

Related questions
See all questions in Choosing between SN1 and SN2
Impact of this question
5265 views around the world
You can reuse this answer
Creative Commons License