questions about nucleophile vs base

[jinzabread]

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when ethoxide (EtO-) or methoxide(MeO-) attack 1st or 2nd alkyhalide, ethoxide acts as base(E2) or nucleophile(Sn2) based on condition. right?
what conditions make it E2 or Sn2?
I only know polar aprotic favors Sn2 and heat favor E2.
and would it make difference if ethanol or methanol or hydroxide were used?
its really confusing.
and what do I have to choose if the problem doesn't specify? and there is no option for both like?
my exam is getting closer and i am getting nervous....
please help me~

 

[docelh]

Should be SN2 favored, with some E2 minor product.

E2 vs. SN2 depends on the substrate and the relative nucleophilicity/basicity of the reagent.

You ask whether you'd get different results if you used methanol, ethanol, and hydroxide; well yes, it's a different reagent. Hydroxide is probably a better nucleophile than alkoxide since it's less sterically hindered.

There are MANY reasons that factor into SN2/E2/SN1/E1. You should review them before your test.