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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: tomallen123 on March 26, 2020, 01:30:01 PM

Title: What are the pKa values of the two amine groups in Carbidopa?
Post by: tomallen123 on March 26, 2020, 01:30:01 PM

What are the rough pKa values of the two amine groups in carbidopa?  Do these amines form a diamine or are they seperate aliphatic amines?  I presumed they would have average pKa values for primary (9.4) and secondary amines (10.7), however drugbank says the most basic group in carbidopa has a pKa of around 5.6.  I am not sure how either of the amines have a pKa value of around this unless both of them being bonded has an effect.

Any responses would be greatly appreciated as this is help for an assignment due very soon.  Many thanks,

Tom.

Title: Re: What are the pKa values of the two amine groups in Carbidopa?
Post by: phth on March 26, 2020, 02:58:18 PM

The mono protonated state would be siginificantly more stable than the diprotonated state. I would guess the 1st pKa is like hydriazine due to the α effect (8.1), and me guessing the 2nd is very low like below 0.  The stable state could be dictated by an intramolecular hydrogen bond, so it is not clear whether or not the primary or secondary nitrogen will be protonated.