Aldol (ald from aldehyde and ol from alcholol) condensation is all about alpha-hydrogen activity and the susceptibility of carbonyl carbons to a nucleophile. This reaction is catalyzed by an acid or a base and it occurs when one aldehyde reacts with another, when keton reacts with another, or when an aldehyde reacts with a ketone. I'll break down the reaction step by step:
1. (Base catalyzed reaction) alpha-hydrogen is abstracted by the base resulting in an enolate ion.
2. The enolate ion acts as a nucleophile and attacks the carbony carbon to form an alkoxide ion.
3. Alkoxide ion removes a proton from water to complete the aldol.
(f.y.i. Alkoxide ion is a stronger base than a hydroxide ion becuase it has an electron donating alkyl group attached to the oxygen, thus increasing it s negative charge.)
The resulting aldol molecule is unstable and is easily dehydrated by heat or a base to become an enal. The enal is stabilized by its conjugated double bonds.
Although this reaction is not as simple as it looks, it is easy to memorize if you keep in mind the acidity of the alpha-hydrogen and the planar configuration of the carbonyl, which makes it susceptible to nucleophilic attack.
This is a must know reaction for the MCAT!!
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