[georgetian3]

The reaction between which pair of reactants occurs the fastest for [OH-] = 0.010 M?

(A) CH₃CH₂CH₂CH₂Cl + OH-
(B) (CH₃)₃CCl + OH-
(C) CH₃CH₂CH₂CH₂Br + OH-
(D) (CH₃)₃CBr + OH

First looking at the leaving group, Br- is a better leaving group than Cl-, hence options A) and B) were removed.

I then thought that, as OH- is a strong base and a strong nucleophile, the reaction should occur through SN2 pathway, which is fastest in primary alkyl halides, hence C)

However, the answers state D). Why would this be faster?

[AWK]

Some compounds react through E1 pathway.

[Babcock_Hall]

It may be that the problem is getting at the rate laws for S_N1 vs. S_N2.  The same logic holds for E1 vs. E2.