The reaction of 2-bromopropane and of its hexadeuterated analogue $(\mathrm{CD}{}_3){}_2\mathrm{CHBr}$ with $\mathrm{NaOEt}$ in ethanol gives $k_{\mathrm{H}}/k_{\mathrm{D}}\approx 6.7$. This large primary kinetic isotope effect shows that:

1. Aa carbocation is formed in the rate-determining step, as in E1
2. Bthe rate-determining step is SN2 attack of ethoxide on carbon
3. Cthe C-Br bond breaks first in a slow step and the C-H bond breaks in a later fast step
4. Dthe C-H (C-D) bond is broken in the rate-determining step, as expected for an E2 mechanism