SN1 and SN2 Reactions Part 2

The SN1 and SN2 examples I have place in substitution reactions should be given further scrutiny. As a practicing synthetic organic chemist, SN1 and SN2 reaction mechanism were not of great concern. Depending on the requirements, reactions would be optimal SN1 or SN2 reactions. Thus, if one needed to form a new bond and if stereochemistry of the product was to be controlled, then an SN2 reaction would be called for. In attempting to accomplish an SN2 reaction, one would use optimal SN2 reaction conditions; good nucleophile, polar-aprotic solvents, and high concentrations.

I note instances in which students are given problems in which they are asked to predict the product(s) of a reaction in which neither of those circumstances are provided. Perhaps these make good questions for some classes, but these only remind me to avoid examples in which this ambiguity might exist. My preference is to provide clear examples of either SN1 or SN2 reactions. I believe students should be able to predict some reactions without any doubt as to what must occur.

As a consequence (even though this is not part of what many students are being asked), students might be able to judge that success and outcome of some reactions might be in doubt. Solvolysis of a secondary chloride in ethanol probably will be a poor reaction (without predicting the product of the reaction). Similarly, addition of sodium bromide to that reaction mixture will not be an effective route for formation of the bromide in an SN2 reaction.

Thursday, December 28, 2006