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Which hydrogen is most acidic?

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Correct Answer: D. E
In order to answer such questions, the stability of each resulting conjugate base should be considered; the more stable this is, the stronger the parent acid.
For enolates, the greater the degree of delocalization of charge, (i.e., the more resonance structures that can be drawn), the stronger the acid. Therefore, proton C is more acidic than B. However, the carboxylate arising from loss of E is the most stable as the charge is shared between two electronegative oxygen atoms (of the CO2– group). Proton E is the strongest acid.

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