Fluorine is more electronegative than Chlorine even then P-Fluorobenzoic acid is weaker acid than P-Chlorobenzoic acid. State the plausible reason for this.
Both fluorine and chlorine are implicated in the −I−I and +M+M effects with the benzene ring (owing to the presence of lone electron pairs). While the −I−I effect tends to increase acidic strength, the +M+M effect tends to decrease it. Because fluorine is more electronegative than chlorine, it has a higher −I−I effect. However, as compared to chlorine, it has a larger +M+M effect (opposing factor). This could be due to the fact that the 2p2p orbitals of carbon and fluorine are similar in size, whereas the carbon and chlorine atoms' orbitals are not. As a result, p−p− fluorobenzoic acid is less potent than p−p−chlorobenzoic acid.
