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Ochem question about basicity of amino group and carboxylate ion at pI?

Discussion in 'DAT Discussions' started by HannibalLecter, Jul 22, 2011.

  1. HannibalLecter

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    when the pH is equal to the pI of a certain amino acid, a zwitterion forms rather than an uncharged molecule. Which of the following must be true concerning the amine group compared to the carboxylate ion?

    the answer says the amino group would be more basic............. but at the isoelectric point wouldn't the amino group would be positively charged and becoming a ammonium ion while carboxylate would be an anion? so wouldnt the ammonium be less of a base because it doesnt have electrons to give up as a base while carboxylate being an ion has electrons and can act like a base?
     
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  3. HannibalLecter

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  4. mh0000

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    I think the question is just asking which terminus group is a better base and which one the better acid. You are right in your analysis of the ionization of each terminus at the pI point. The amino group is fully protonated because it is a better base, while the carboxylic acid will be deprotonated because it is a weaker base/stronger acid. So really they just give you a hint/the answer in the description of the question.
     

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