Question
Base-Catalyzed Aldol Condensation:
Aldol Addition
Step #1: The base removes an α-hydrogen,
leaving an enolate ion.
Step #2: ____.
Step #3: Alkoxide ion removes
a proton from water, completing the aldol and leaving behind the weaker hydroxide ion conjugate base.
Aldol Condensation
Step #4: Treat Aldol with strong base and high temperatures to lose a water molecule (H+ and OH-), to form the final product, a α,β-unsaturated aldehyde.
Answer
Base-Catalyzed Aldol Condensation:
Aldol Addition
Step #1: The base removes an α-hydrogen,
leaving an enolate ion.
Step #2: The enolate ion then acts as a nucleophile, att~cking the
carbonyl carbon of the other aldehyde or ketone and creating an alkoxide ion.
Step #3: Alkoxide ion removes
a proton from water, completing the aldol and leaving behind the weaker hydroxide ion conjugate base.
Aldol Condensation
Step #4: Treat Aldol with strong base and high temperatures to lose a water molecule (H+ and OH-), to form the final product, a α,β-unsaturated aldehyde.
Tip: When you see a carbonyl reaction,
ask yourself if the carbonyl was
attacked (more common) or if the
carbonyl was the attacker. If you
see a change in what was attached
to the carbonyl carbon, the
carbonyl carbon was attacked by a
nucleophile and either an addition (aldehyde or ketone becomes an
alcohol) or a substitution reaction
(carbonyl with a new leaving group)
took place. If the original carbonyl
is intact with a new bond to the
alpha carbon, the alpha carbon of
the carbonyl actd as a nucleophile
(carboxylate or enolate).
Note: In biochemistry, enzymes act as catalysts for any chemical reaction; and the class of enzyme that catalyzes aldol reactions is called, quite intuitively, 'aldolase'. Let’s now discuss the first step of Kreb’s cycle: acetyl coenzyme A (acetyl CoA) condenses with oxaloacetate to produce (S)-Citryl CoA through an aldol mechanism. Here, instead of an aldehyde or a ketone, a thioester acts as the nucleophilic partner
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