topscore mistakes?

[rav4182]

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i just took topscore exam 1 and am confused about some potential errors on the exam.

Aldol Condensation- there was a question on it. Someone please correct, dehydration ONLY occurs if heat is present right? in the question there were no other reagents after H3O+ so wouldnt the final product be a hydroxy ketone or something???? top score said the answer was the dehydration product.

r/s configuration- there was a simple question about assigning absolute r/s. but there were no perspective lines on any of the molecules. all the lines were solid. is this an error or something? dont you need to know which bonds are dashed and wedged to assign configurations?


edit: i found the reason why the r/s was confusing. They were actually fischer projections which explains why you dont need wedged/dashed line. normally i dont problems with fischer projections, but i guess this question was weird because they still drew in the C in the center.

 

[rav4182]

no one knows about the aldol condensation????

 

[voager]

Aldol products can often undergo dehyderation (loss of water) to give conjugated systems (an elimination reaction). Try to identify the enolate portion and the carbonyl portion in the different representations. also I can help more if I can see the question..... as of right now I am thinking adol condensation of aldehydes and ketones ..so reagents are necessary to know and only H3O+ is not helping.

see the attachemnts for aldehyde and ketone aldol condensation reactions. (open attachments in new window or tab if you see blank image)


Regarding your fisher projections:
In a Fischer projection, all horizontal bonds project toward the viewer, while vertical bonds project away from the viewer. hope you know how to work out the fisher Projection for R/S compounds if not let me know and I can post explanation here.

 

[rav4182]

ok i understand a lot better now. the question had a benzene ring in it and the answer was conjugated. i hadnt seen that before but i know now, thanks.

SO, is it safe to say aldol condensation can have dehydration without heat if it yields a conjugaed system?

 

[voager]

yes