The second part has two steps that accomplish the elimination of water. Normally, alcohols do not undergo dehydration in the presence of a strong base, but here, the presence of the carbonyl group enables the dehydration reaction to occur. The a position is first deprotonated to form an enolate ion, followed by expulsion of a hydroxide ion to produce a,b unsaturation. This two-step process, which is different from the elimination reactions we saw in Chapter 8, is called an E1cb mechanism. In an E1cb mechanism, the leaving group only leaves after deprotonation occurs.