The relative acidity between carboxylic acids has been used as ameans for determining the electron-withdrawing or electron-donatingabilities of substituents.
a) The pKa of phenyl acetic acid is 4.31, making it a strongeracid than acetic acid. Is the Ph group electron-donating orelectron-withdrawing in this case?
b) The Ph group is a mild o,p-director in EAS reactions. Is thePh group electron-donating or electron-withdrawing? If the answercontradicts your answer from part a, provide an explanation.
c) 4-Methoxybenzoic acid is a weaker acid than benzoic acid, yetmethoxyacetic acid is a stronger acid than acetic acid. Rationalizethese seemingly contradictory results.
d) Methyl groups are usually considered electron-donatinggroups. Propanoic acid is a weaker acid than acetic acid. Is thatresult in agreement?
