7. Substitution Reactions

Which of the following alkyl halides is most likely to undergo an $S_{N2}$ reaction rapidly?

Given the following alkyl halides: 1. $\mathrm{CH}{3}_{\mathrm{Br}}$ (methyl bromide), 2. $\mathrm{CH}{3}_{\mathrm{CH}}{2}_{\mathrm{Br}}$ (ethyl bromide), 3. $\left(\mathrm{CH}{3}_2\right)\mathrm{CHBr}$ (isopropyl bromide), 4. $\left(\mathrm{CH}{3}_3\right)\mathrm{CBr}$ (tert-butyl bromide), rank them from most to least reactive in an $S{N}_2$ reaction.

Which of the following is the major organic product formed when ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{Br}}_1$ reacts with ${\mathrm{OH}}_1-$ in an $S{N}_2$ reaction?

Examine the two $S{N}_2$ reactions below: (A) ${\mathrm{CH}}_3\mathrm{Br}$ with $\mathrm{OH}-$ and (B) ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}$ with $\mathrm{OH}-$. Which reaction will proceed at a faster rate?