Chemistry - GOC Question with Solution | TestHub

All three are fluorobenzoic acids; fluorine stabilises the carboxylate by its -I effect, and the effect grows with proximity to COOH. In (a) the F is para, where its -I effect is weakest on the carboxylate ($\mathrm{p}{K}_{\mathrm{a}}$ 4.14). In (b) the ortho F withdraws strongly through the short path ($\mathrm{p}{K}_{\mathrm{a}}$ 3.27). In (c) both ortho positions carry fluorine, doubling the stabilisation ($\mathrm{p}{K}_{\mathrm{a}}$ ≈ 2.2). Hence (a) $<$ (b) $<$ (c).