[rjt027]

Question is: Which of the following undergoes substitution by the Sn2 mechanism at the fastest rate?

1) 2-bromobutane
2) 2-bromo-1-butene
3) 1-bromo-2-methylpropane
4) 1-bromo-2-methyl-1-propene
5) 1-bromobutane

My first thought is that #5 will react the fastest due to it being a primary alkyl halide & the least amount of steric hindrance.

First: Find Primary/Secondary/Tertiary/etc
Second: Look at steric hindrance...
Third: ?

Am I missing anything of relevence in determining which one will react the fastest in Sn2?

[TwistedConf]

My first thought is that #5 will react the fastest due to it being a primary alkyl halide & the least amount of steric hindrance.

First: Find Primary/Secondary/Tertiary/etc
Second: Look at steric hindrance...
Third: ?

Am I missing anything of relevence in determining which one will react the fastest in Sn2?

2 and 5 won't react at all in an SN2 reaction.  After that, your sterics argument is good and your choice seems correct.

[Babcock_Hall]

@OP, What do you know about vinyl bromides and S_N2 reactions?