Urocanic acid is an intermediate in the catabolism of histidine.


 
(a) Determine which nitrogen of urocanic acid is basic and which one is not.
(b) Using resonance forms, show how the protonated form of urocanic acid is a particularly stable cation.
(c) Draw the structures of urocanic acid showing protonation at the basic nitrogen and then deprotonation of the other nitrogen.

• A.
• B.
• C.
• D.

Answer: (A)