The latter attack can lead to an elimination reaction. We will look at elimination reactions in more detail in a week or so, but we can usefully examine them as competitors for S N 1 and S N 2 reactions just now. When we first learned about the Williamson ether synthesis, we learned that it works best when the alkyl halide is primary. However, a patient person might suggest that even a slow S N 2 reaction might succeed if we were willing to wait a while. What defeats this strategy is that the alkoxide ion can also react as a base.
Elimination reactions are always potential competitors for substitution reactions.
The presence of a strong base like an alkoxide or hydroxide ion. Solvolysis of a tertiary alkyl halide using an alcohol as both nucleophile and solvent can make an ether very effectively. Of course, this is only possible when the desired nucleophile can be used as a solvent as is the case for alcohols and water. To finish up today, let's revisit some reactions of alcohols and see if we can use the S N 1 or S N 2 pattern to understand them a little better. This looks like a nucleophilic substitution and since the alkyl group is tertiary, the S N 1 pathway through a carbocation intermediate looks like a good guess.