Aldol Condensation

[wooj0313]

I am now studying for aldol condensation and come up with some questions

1. how do we know if my aldol condensation has the correct stereo-chemistry?

2. how do we tell if aldol product reacts with one equivalent of aldehyde instead of two equivalents of aldehyde ( reaction between ketone and aldehyde)?

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[SKaminski]

Maybe I'm understanding Aldol Condensations poorly, or i'm understanding your questions poorly but:

1)An Aldol Condensation is a reaction in which the carbonyl carbon of one carbonyl group attacks the alpha carbon of a second carbonyl group. This can occur over 2 molecules, or just one. This initially creates an alcohol, which (through condensation) is reduced to a double bond.

So, for stereo-chemistry: Carbonyl groups have planar stereo chemistry. You're fine there. As for the 'stereo-chemistry of the double bond, I believe you will get a mixture of both Z and E.

2) I believe you would get a mixture of both, when one solution predominating. Remember: an alpha-beta unsaturated carbonyl will react very readily at the alpha carbon because it is resonance stabilized. I think I could use more information here as well. Hope this helps!

 

[Laureatebarrel]

Unsaturated beta-alpha carbonyl get 1-4 addition which means nucleophile will attack the beta carbon not the alpha carbon (draw resonance will show you that the beta carbon has a partial positive charge)