Acidity of Carboxylic Acids
For each of the following pair of molecules, choose which would be more acidic and explain why.
Remember that acidity is based on the stability of the conjugate base. Whichever molecule has a more stable conjugate base will be more stable.
The amino group is electron donating by resonance which would destabilize the carboxylate (conjugate base of the acid) making the para-aminobenzoic acid less acidic than benzoic acid.
The nitro group is electron withdrawing by resonance which would stabilize the carboxylate making the para-nitroobenzoic acid more acidic than benzoic acid.
The fluoro group is more electronegative than chloro, therefore will inductively stabilize the carboxylate better than the chloro group will.
The 1,1-dichloropropanoic acid has two groups that withdraw electron density inductively thereby stabilizing the carboxylate more than the mono chloro molecule.
For the following amino acid, draw the structure under acidic, neutral and basic conditions.
Under acidic conditions both the carboxylate and the amine are protonated and the molecule has an overall charge of +1.
Under neutral conditions, the amine is protonated while the carboxylate is deprotonated giving the overall charge neutral.
Under basic conditions, the amine is not protonated and neither is the carboxylate. The molecule will have an overall charge of -1.
What makes glycine different from all other amino acid residues that constitute proteins?
- Layne Morsch (University of Illinois Springfield)