Organic Acids

Which one is more acidic, p-fluorobenzoic acid or p-bromobenzoic acid and why?

5 Answers

106
Bitan Chakraborty ·

The p-orbital overlap is much more effective when the overlapping orbitals are of comparable size and so the +R effect of fluorine (which uses 2p orbital) is greater than the effect of bromine (which uses 4p orbital). Infact, the +R and +I effects of F are nearly counterbalanced, whereas the +R effect of Br is weaker than its +I effect. Therefore, although both halogen atoms tend to lower the electron density of the ring, the lowering is much effective in Br-acid than F-acid. Hence, p-fluorobenzoic acid is LESS acidic than p-bromobenzoic acid.

145
Ranadeep Roy ·

p-bromobenzoic acid I guess, as there will be H-bonding in case of p-fluorobenzoic acid

79
Tanumoy Bar ·

p-fluorobenzoic flourine increases electrinegativity.

996
Swarna Kamal Dhyawala ·

p bromobenzoic acid will be more acidic as it contains more acidic hydrogen..
In p-fluorobenzoic acid there is backbonding so the acidity decreases

79
Tanumoy Bar ·

Thank u Sir this ques came in WBJEE this year.

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