Answer to Question #305099 in Organic Chemistry for Karly

Question

Use electronic and stability factors to account for the acidity of each hydrogen in

the m-hydroxybenzoic acid. Identify the most acidic proton.

Answer 1

OH group has two effects, namely +R and -I effect i.e. Resonance and Inductive effect. When -OH group is attached to the para position, it has a tendency to delocalize it's electrons towards the aromatic ring (that is, benzene). Thus the electron density on oxygen atoms of carboxylic group increases and the polarity between O and H decreases leading to less acidity. Whereas when the -OH group is attached to the meta position, +R effect is not applicable and only -I effect is effective. Thus it withdraws the electrons from the ring, and increasing the polarity between O and H in carboxylic group, making it more acidic.