Alkoxides are important nucleophiles, and the SN2 reaction of an alkoxide with an alkyl halide is the basis of the Williamson ether synthesis. As an electron donor, sodium ethoxide is most attracted to the electrophilic carbon that bears bromine. The ethoxide anion does indeed collide with that carbon. The activation barrier for a SN2 reaction with a tertiary halide is too high due to steric hindrance in the transition state. Cyclic halides with a secondary or tertiary center undergo E2 reactions when treated with base. There is greater conformational flexibility in cyclohexane derivatives and both cis- and trans-derivatives react. Once the carbocation intermediate is formed, both the nucleophilic hydroxide ion and water can collide with the positive carbon of the carbocation.