ochem question 76 on first topscore test?

[marmar]

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so how do we know that aldose condesation will end up with loosing a water molecule? I thought we know so if we see heat at the end. but this question just adds base and acid and no heat. any idea?

 

[drgreen]

I didn't look at the question, but if there's a benzene near the aldol, the loss of H2O occurs w/o heat.

 

[marmar]

oh ok I do not understand why but there was a benzene there and I assume that is why. do you know why that is the case?

 

[drgreen]

k, check it out...

The benzene stabilizes the carbocation formed (resonance via pi system) when OH leaves via Sn1. I just bade up this RXN, idk what the topscore version is. But try to understand the mechanism.

 

[marmar]

thanks, this is amazing.