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phenitoin

Can you explain why phenitoin is weak acid even though nitrogen is base? Does carbonyl group always make structure acid? If this structure doesn't have carbonyl group, would it be base not acid?

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  • $\begingroup$ The NH between the carbonyls is in a similar position to succinimide. The negative charge on losing the proton can be delocalised across both carbonyls. $\endgroup$ – Waylander Apr 27 at 6:59
  • $\begingroup$ @Waylander So shouldn't it's acidity be more as the negative charge is in resonance with two carbonyls? It should be a good acid in my opinion, although that is a relative term. $\endgroup$ – Light Yagami Apr 27 at 10:31
  • $\begingroup$ Depends on your definition of a good acid. Succinimide has pKa 9.3, Phenytoin is 8.3. That makes it a stronger acid than phenol (pKa 10). It forms a stable sodium salt. $\endgroup$ – Waylander Apr 27 at 11:48
  • $\begingroup$ I see. Then why doesn't the lone pair on nitrogen move? Plus I could understand this structure can resonance so which can it be acid or base? $\endgroup$ – iwamoto 4477 Apr 29 at 0:34
  • $\begingroup$ When pheytoin lose proton as acid and the resonance structure is stable, isn't it strong acid? Because the strong acid is made when the resonance structure is stable(can resonance) Sorry, if I'm wrong though.. $\endgroup$ – iwamoto 4477 Apr 29 at 0:39

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