[limonade]

Why is this reaction preferred SN2 and not SN1?

[Dan]

What is "OH"? Do you really mean an OH radical?

[orgopete]

I presume hydroxide anion is "OH". This is one of those semi-ambiguous areas. A secondary halide with a strong base will give elimination. However, if we were bang asked to describe how a substitution product might form, then we can ask whether it should be SN1 or SN2? My rule of thumb is that just as the kinetics are controlled by concentrations, then by virtue of listing [OH(-)] as a reagent implies that it should have a kinetically important role in the reaction. That, by definition, leads to it being SN2. That is, its concentration can be increased to greater and greater levels to increase the reaction rate. If no such effect were present, then it would react as though hydroxide were not even present, hence SN1-like.

[limonade]

Thank you

[Mr. Inquisitive]

It's SN2 because the OH ion acts as the nucleophile who will donate its electron pair to the oxygen in DME (dimethyl ether).

[Babcock_Hall]

DME is the solvent, not a reactant, unless I am missing something.