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Question

Chemistry Question on Aldehydes, Ketones and Carboxylic Acids

What will be the correct decreasing order of acid strength of the hydroxybenzoic acids? (Symbols and notations carry their usual meanings)

A

pp-Hydroxybenzoic acid >> benzoic acid >m> m-hydroxybenzoic acid >o> o-hydroxybenzoic acid

B

oo-Hydroxybenzoic acid >m> m-hydroxybenzoic acid >> benzoic acid >p> p-hydroxybenzoic acid

C

oo-Hydroxybenzoic acid >> benzoic acid >m> m-hydroxybenzoic acid >p> p-hydroxybenzoic acid

D

mm-Hydroxybenzoic acid >> benzoic acid >o> o-hydroxybenzoic acid >p> p -hydroxybenzoic acid

Answer

oo-Hydroxybenzoic acid >m> m-hydroxybenzoic acid >> benzoic acid >p> p-hydroxybenzoic acid

Explanation

Solution

In case of hydroxybenzoic acids, they display both kind of effect and there is a decrease in electron density at all positions due to inductive effect of OH-OH group, but increase in electron density at oo- and pp- positions due to resonance effect by OH-OH group . So, oo- p-hydroxybenzoic acids should be weaker than m-hydroxybenzoic acid, but oo-hydroxybenzoic acid is strongest due to stabilisation of anion by hydrogen bonding