Why Is This Considered an SN2 Reaction?

[phEight]

Homework Statement

CH3CH2-Br + (CH3)3C-O¯+K ----> (CH3)3C-O-CH2CH3
ethylbromide + potassium t-butoxide ---> ethyl t-butyl either

can someone please tell me why this is a Sn2 reaction?

Homework Equations

The Attempt at a Solution

I figured it should be Sn1 because the nucleophile is tertiary, but that is not the case. Is it because O is primary? Even then the nucleophile seems very crowded for an Sn2 reaction. Thanks in advanced.

 

[Kalirren]

The whole reason why tertiary/secondary/primary substitution level matters is that it stabilizes the intermediate carbocation, i.e., substitution level matters on the electrophile, not the nucleophile. It doesn't matter whether the nucleophile is tertiary or primary.

CH3CH2-Br is synthetically equivalent to CH3CH2(+) - hence, it is the electrophile. Since the electrophile is primary, and there is no resonance stabilization of the carbocation, the reaction is likely to proceed by an SN2 mechanism.