What Is the Aldol Reaction

Treatment of an aldehyde or a ketone containing an acidic a-hydrogen with a strong base, such as sodium hydroxide or sodium ethoxide, gives an enolate anion as a hybrid of two major contributing structures  

Given the relative acidities of the two acids in this equilibrium, the position of equilibrium lies considerably to the left. However, the existence of just a small amount of enolate anion is enough to allow the aldol reaction to proceed. 

Addition of the enolate anion derived from an aldehyde or a ketone to the carbonyl group of another aldehyde or ketone is illustrated by these examples  

The common name of the product derived from the reaction of acetaldehyde in base is aldol, so named because it is both an aldehyde and an alcohol. Aldol is also the generic name given to any product formed in this type of reaction. The functional group of the product of an aldol reaction is a /3-hydroxyaldehyde or a /3-hydroxyketone. 

The key step in a base atalyzed aldol reaction is nucleophilic addition of the enolate anion from one carbonyl-containing molecule to the carbonyl group of another carbonyl-containing molecule to form a tetrahedral carbonyl addition intermediate. This mechanism is illustrated by the aldol reaction between two molecules of acetaldehyde. Notice that OH is a true catalyst An OH is used in Step 1, but another OH is generated in Step 3. Notice also the parallel between Step 2 of the aldol reaction and the reaction of Grignard reagents with aldehydes and ketones (Section 12.5) and the first step of their reaction with esters (Section 14.7). Each type of reaction involves the addition of a carbon nucleophile to the carbonyl carbon of another molecule. 

---

They Formed What Is the Aldol Reaction 15.3 Used in a Ciaisen Condensation How to Determine the Starting Compounds... 

---