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Fluorine is more electronegative than chlorine even then p-fluorobenzoic acid is a weaker aci than p-chlorobenzoic acid. Explan. |
Answer» Solution :Since halogens are more ELECTRONEGATIVE than carbon and also POSSESS lone pairs of ELECTRONS, therefore, they exert both -I- and +R- EFFECTS. Now in F, the lone pairs of electrons are present in 2p-orbitals but in Cl, they are present in 3p-orbitals. since 2p-orbitals of F and C are of almost equal size, therefore, the effect is more pronoiunced in p-fluorobenzoic acid than in p-chlorobenzoic acid.  Thus, in p-fluorobenzoic acid, +R-effect outweighs the -I-effect but is p-chlorobenzoic acid, it is the -I- effect which outweighs the +R-effect. consequently, p-fluorobenzoic acid is a WEAKER acid than p-chlorobenzoic acid. |
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