[aram2189]

I have a question regarding the reaction below:

2-bromopropane is reacted with sodium ethoxide in ethanol to give 2-ethoxypropane and 1-propene.

The answer states that the reaction would be Sn2/E2 and this is where I have a problem, discerning whether the reaction is Sn2/E2 or Sn1/E1.  The substrate would be a 2° halide, so that does not give us any insight. Sodium ethoxide is a strong small nucelophile which would indicate an Sn2/E2, but the solvent used is ethanol, a polar protic solvent, which should favor Sn1/E1. So why is it Sn2/E2 and not Sn1/E1? Does the nucleophilicity of the nucelophile take precedence over the solvent used? My professor once told me that even though Sn2/E2 reactions prefer a polar aprotic solvent, the reaction can still occur in a polar protic solvent and vice versa (except it would be much slower). How should I be examining this reaction?

[Nescafe]

From my understanding it is true that a polar solvent stabilizes the carbocation specie favouring a SN1  type of mechanism or E1 in presence of a strong base. But I think the reason it is only SN2/E2 in this case it is because the solvent is ethanol which is in an equilibrium with your base/nucleophile (I.e. ethoxide). So although it is polar protic, since its ethanol/ethoxide, it only proceeds via E2/SN2.

And just to add another point, for a SN1/E1 to be favoured for a secondary carbocation which is not as stable as a tertiary carbocation or one where the charge is delocalized (e.g. Trityl chloride gives a resonance stabilized carbocation) you usually require a weak nucleophile/or base (e.g. H2O). In this scenario, the carbocation has enough time to form before the nucleophile comes in. Ethoxide is a strong nucleophile and a strong base, therefore SN2/E2 is favoured.

If your solvent was butanol I would say it does not make sense.

That's my understanding anyways,

Nescafe.