Acidic Strength - Ortho Effect (Aromatic Acids)

Structural Reactivity Framework:

Ortho-Substituted Benzoic Acid > Benzoic Acid (Valid for nearly all functional groups)

Concept: Outlines a unique structural anomaly where any substituent placed adjacent to the carboxyl group on a benzene ring drastically boosts proton release capacity. The bulky ortho-group forces the carboxylic acid moiety out of the aromatic plane, disrupting conjugation with the ring (Steric Inhibition of Resonance) and localizing the negative charge strictly over the two symmetric oxygens.

Notation:

• $$\text{SIR}$$ = Steric inhibition of resonance; Independent of electronic nature (holds true for both withdrawing and donating groups).