destroyer 2011 org #157

[Hope30]

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Hello guys, i do not understand the second part of #157 when alcohol and water reacted with aldehyde to form an aldol product. How come? The first thing it comes to my mind is that the product is a carboxylic acid. Aldol is unexpected. Thanks for the help.

 

[Demps]

Hello guys, i do not understand the second part of #157 when alcohol and water reacted with aldehyde to form an aldol product. How come? The first thing it comes to my mind is that the product is a carboxylic acid. Aldol is unexpected. Thanks for the help.

Simply think of what is a better leaving group. This might help you clarify. After aldehyde forms with PCC. OH- will rip off an alpha hydrogen and hence aldol reaction takes places.

Say OH- did attack the carbonyl and and give you diolate (I'm not sure what you call this - two alcohol group to the same carbon, but one of the oxygen being ionized) and you would see that OH- (or water) will be a better leaving group than hydrogen. hydrogen wouldnt leave. COOH does not result.

Hope this helped.

 

[rah08e]

if your answer is a beta hydroxy ketone, then this is just a simple aldol condensation reaction. Whenever you see something like an aldehyde reacted with -OH and H2O, you assume 2 mols of the aldehyde.