April 19, 2019, 04:41:27 AM
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Topic: Acidity rankings and aldol condensation practice: Have I done this right?  (Read 815 times)

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Offline DiethylEtherIsCute

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My professor gave us this sheet (https://i.imgur.com/SAbPCX5.jpg) to work on yesterday. 

I'm pretty confident about my ranking of the acidity of the compounds, and I think I'm right about the aldol condensation mechanism -- please correct me if there are mistakes! 

On the other hand, I'm not sure where to start with #2.  It looks like an aldol cyclization, since the product has the alkene and the C=O in conjugation, but I am not 100% sure about what the starting material or the mechanism would be.  I at least know that the starting material is going to be a chain containing two enolizable carbonyl groups, but I need to know the correct answer because my prof. is definitely going to quiz us on this next class.
« Last Edit: April 17, 2018, 12:53:16 PM by DiethylEtherIsCute »

Offline pgk

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1). If you have acidic conditions, you don’t need the base B:, erase it immediately, because it is a serious mistake. Just continue by drawing an acidic dehydration and that’s all.
2). Try a retro-synthesis and go back:
2-Cyclohexenone ←  3-hydroxy-cyclohexanone ← ? (= a six member aliphatic aldehyde containing a ketone group at the end.)
3). Ignore the methoxide catalysis for the moment. But for your own and further information, this reaction involves a cyclization step that has a higher activation energy and therefore, strong catalysis is needed. On the other hand, strong basic conditions avoid the simultaneous double aldolization of a ketone by an aldehyde, contrary to strong acidic conditions that favor it.
« Last Edit: April 17, 2018, 02:10:24 PM by pgk »

Offline crawlingmcedge

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I'll assume that you know what an elimination reaction is. What functional groups can be eliminated to turn to alkenes? Where would that functional group be placed in on that ring?

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