Reactions of enolates with aldehydes and ketones the aldol reaction

Reactions of enolates with aldehydes and ketones the aldol reaction 

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The simplest enolizable aldehyde is acetaldehyde (ethanal, CH3CHO). What happens if we add a small amount of base, say NaOH, to this aldehyde Some of it will form the enolate ion. 

Only a small amount of the nucleophilic enolate ion is formed hydroxide is not basic enough to enolize an aldehyde completely. Each molecule of enolate is surrounded by molecules of the aldehyde that are not enolized and so still have the electrophilic carbonyl group intact Each enolate ion will attack one of these aldehydes to form an alkoxide ion, which will be protonated by the water molecule formed in the first step. 

The product is an aldehyde with a hydroxy (ol) group whose trivial name is aldol. The name aldol is given to the whole class of reactions between enolates (or enols) and carbonyl compounds even if in most cases the product is not a hydroxy-aldehyde at all. Notice that the base catalyst (hydroxide ion) is regenerated in the last step, so it is truly a catalyst. 

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