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explain the order of acidity o-hydroxy benzoic acid >m hydroxy benzoic acid> benzoic acid>p-hydroxy benzoic acid

explain the order of acidity o-hydroxy benzoic acid >m hydroxy benzoic acid> benzoic acid>p-hydroxy benzoic acid


 

Grade:12

4 Answers

Palash Gupta
20 Points
12 years ago
o-hydroxy benzoic acid is most acidic because after loosing H+ the COO- is stablised by H-Bonding with OH group.

m hydroxy benzoic acid is next due to -I effect of OH group it's acidic character increases (due to -I effect e- density at O-H bond of COOH is reduced and loss of H+ becomes easy.) but there is no +M effect of OH at meta pos.(+M is exerted only at o,p pos.) so m-hydroxy benzoic acid is more acidic than benzoic acid.

p-hydroxy benzoic acid is least acidic because +M effect of OH group at p pos. decreses it's acidic character (due to increase in e- density at O-H bond). As +M effect of OH is stronger than it's -I effect increase in acidity due to -I effect cannot compensate for it.
Yash Sinha
32 Points
12 years ago
o-hydroxy benzoic acid on losing H+ forms conjugate base which is highly stable as it forms  H-bond
Dipanwita susie
11 Points
7 years ago
O-hydroxy benzoic acid is the most acidic as there is hydrogen bonding...now between Kara and meta in the meta position there is no effect of resonance, so only -I effect of oh- comes into play here...in para position, -I effect of oh- increases the electron density on coo- so it is less acidic. Hence the acid strength will be ortho>meta>para
Bhuvnesh
11 Points
7 years ago
The first answer is most appropriate,just remember afact: in most cases o- substituted benzoic acids are most acidic regardless of their nature(electron with drawing or donating)😊

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