Chapter 18: Enols and Enolates 
Ch 18 contents
The Aldol Condensation of Aldehydes
Aldol condensation of an aldehdye
Reaction type : Nucleophilic addition

Summary

Aldol condensation of ethanal
Try to identify the enolate portion and the carbonyl portion in the different representations
Highlight enolate component Nu
Highlight carbonyl component E
Question
Why isn't the simplest example of an aldol the condensation of methanal ? methanal, CH2O has no alpha H so it can't form an enolate
loss of water gives a C=C in a conjugated aldehyde
STUDY TIPS:
taking an Aldol reaction apart to find the pieces
Related Reactions
MECHANISM OF THE ALDOL CONDENSATION

Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic a-hydrogen giving the reactive enolate.
mechanism of the Aldol condensation
Step 2:
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
Step 3:
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the b-hydroxyaldehydes or aldol product.

 
 
MECHANISM OF THE DEHYDRATION OF THE ALDOL PRODUCT

 

Step 1:
First, an acid-base reaction. Hydroxide functions as a base and removes an acidic a-hydrogen giving the reactive enolate.

mechanism of the dehydration of an Aldol product
Step 2:
The electrons associated with the negative charge of the enolate are used to form the C=C and displace the leaving group, regenerating hydroxide giving the conjugated aldehyde.


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