Aldol Condensation

[utdent20]

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Can someone explain aldol condensation in layman terms to me.. 104 on o chem destroyer is a good problem.. but i don't understand it.. Please Help!!

 

[Commitment]

aldol condensation means you have 2 x aldehydes plus a base (most cases OH-). the base will rip off an H on the C right next to the C=O aka alpha hydrogen. this one aldehyde now has a negative charge making it an "enol". now it acts like a nucliophile (with the - charge on the alpha carbon) and attacks the other aldehyde from before.

Main pt: the alpha carbon from one aldehyde connects to the 2nd aldehyde on the C=O via nucleophilic addition making a molecule that has an aldehyde and an alcohol one C away from each other...

(NOT nucleophilic sub, which would bounce off a leaving group. since there arent any LG's, substitution wont happen here...)

What heat does, and remember, heat needs to be added to make this this problem in particular to work, does dehydration (loss of H2O and form a DB. the DB forms from the C where the -OH was with the carbon next to it that has the LEAST number of H's)...

 

[wbloo]

good explanation!

 

[MoooShuuu]

If no heat is added but there is H3O+ present, does it do the same thing as heat and takes off the -OH and forms the C=C?

 

[yankees27th]

Can someone explain aldol condensation in layman terms to me.. 104 on o chem destroyer is a good problem.. but i don't understand it.. Please Help!!

Hey, I've been lurking this forum for a while now and have finally decided to contribute haha.
For ochem destroyer 104, first the PCC gives you a 2-carbon aldehyde (ethanal, aka acetaldehyde, which happens to be choice A). The OH pulls a hydrogen off of the carbon NEXT TO the carbon that is double bonded to the oxygen. This carbon then attacks the carbonyl carbon (the one with the double bond to oxygen) of a different molecule. The oxygen belonging to the carbonyl carbon that is attacked ends up being protonated to form an alcohol. That is the end of the aldol part of the reaction and you have choice C. However, heat causes dehydration and you get a double bond, which is choice E.
Keep in mind that an aldol reaction with a 2 carbon starting material will get you a 4 carbon product so you can immediately eliminate choices A and D.
If this doesn't make sense let me know and I can try to insert a picture.

 

[supraman]

Know Aldol for DAT, it was on mine.

 

[Dencology]

good pic. i wanted to know how did you cut and paste this. i tried to do this and i can't. let me know. thx
by the way. LET"S GO LAKERS. I SEE YOU IN FINAL. LAKERS in 6.

 

[supraman]

good pic. i wanted to know how did you cut and paste this. i tried to do this and i can't. let me know. thx
by the way. LET"S GO LAKERS. I SEE YOU IN FINAL. LAKERS in 6.

Although Lakers are undefeated right now, C's are right behind them with 7-1 record. I feel another finals Lakers-Celtics series, but I don't think David Stern will want that lol.

1. Click on this:

2. paste the link in the prompt window
3. thats it