Is fluoro benzoic acid more acidic than chloro benzoic acid?
Answers
Answer:
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Explanation:
Halogens show two types of effects when attached to a phenyl group:
1. —I effect (Inductive effect) which deactivates the rings by pulling electrons towards it and increases the acidity (reduces pH)
1. + M effect (Mesomeric effect) because of presence of lone pair of electrons which activates the ring and decreases acidity (increases pH).
Fluorine is more electronegative than chlorine, so logically, fluorobenzoic acid should be a stronger acid than chlorobenzoic acid. This is not the case. Why?
Inspite of being more electronegative than chlorine, fluorine has a stronger +M effect because of resonance between 2p orbital of fluorine and 2p orbital of the carbon attached to it. This +M effect is weaker than that of chlorine which is caused due to resonance between 3p orbital of chlorine and 2p orbital of carbon.
Hence, p-fluorobenzoic acid is a weaker acid than p-chlorobenzoic acid.
Explanation:
Inspite of being moreelectronegative than chlorine, fluorine has a stronger +M effect because of resonance between 2p orbital of fluorine and 2p orbital of the carbon attached to it.