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What is the acidic trend of benzoic acid and meta-, para-, ortho-nitrobenzoic acid?
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Katrina Johnston
What is the acidic trend of benzoic acid and meta-, para-, ortho-nitrobenzoic acid?
o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid. This is because of two reasons:
Ortho Effect
Inductive Effect
Talking about the first one, Due to presence of nitro group on ortho position, the -COOH group bends out of the plane of the ring due to steric hindrance. As a result, H+ ion can be easily removed because it has come out of the plane of ring.
The nitro group also withdraws electron density by inductive effect. When H+ ion is liberated, the negative charge on oxygen is reduced a little due to withdrawing effect of nitro group. The near the group, more is the inductive effect. Hence, nitro group on ortho position has higher inductive effect compared to the nitro group on para position. The stability of the anion formed after liberation of H+ is directly proportional to the acidity of a compound.
Hence, due to these 2 reasons, o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid.
o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid. This is because of two reasons:
Ortho Effect
Inductive Effect
Talking about the first one, Due to presence of nitro group on ortho position, the -COOH group bends out of the plane of the ring due to steric hindrance. As a result, H+ ion can be easily removed because it has come out of the plane of ring.
The nitro group also withdraws electron density by inductive effect. When H+ ion is liberated, the negative charge on oxygen is reduced a little due to withdrawing effect of nitro group. The near the group, more is the inductive effect. Hence, nitro group on ortho position has higher inductive effect compared to the nitro group on para position. The stability of the anion formed after liberation of H+ is directly proportional to the acidity of a compound.
Hence, due to these 2 reasons, o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid.
The nitro group (NO2) is always electron withdrawing either by resonance (ortho or para position) or induction (ortho or meta positions) and will stabilize formation of the carboxylate and H+. Both factors (resonance and induction) contribute in the ortho position while only resonance in the para position so the ortho derivative will be a stronger acid relative to the para. Also, since resonance effects are greater than inductive when comparing the meta and para positions, this consideration will put the order of acidity, from strongest to weakest, as
The nitro group (NO2) is always electron withdrawing either by resonance (ortho or para position) or induction (ortho or meta positions) and will stabilize formation of the carboxylate and H+. Both factors (resonance and induction) contribute in the ortho position while only resonance in the para position so the ortho derivative will be a stronger acid relative to the para. Also, since resonance effects are greater than inductive when comparing the meta and para positions, this consideration will put the order of acidity, from strongest to weakest, as
o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid. This is because of two reasons:
Talking about the first one, Due to presence of nitro group on ortho position, the -COOH group bends out of the plane of the ring due to steric hindrance. As a result, H+ ion can be easily removed because it has come out of the plane of ring.
The nitro group also withdraws electron density by inductive effect. When H+ ion is liberated, the negative charge on oxygen is reduced a little due to withdrawing effect of nitro group. The near the group, more is the inductive effect. Hence, nitro group on ortho position has higher inductive effect compared to the nitro group on para position. The stability of the anion formed after liberation of H+ is directly proportional to the acidity of a compound.
Hence, due to these 2 reasons, o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid.
o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid. This is because of two reasons:
Talking about the first one, Due to presence of nitro group on ortho position, the -COOH group bends out of the plane of the ring due to steric hindrance. As a result, H+ ion can be easily removed because it has come out of the plane of ring.
The nitro group also withdraws electron density by inductive effect. When H+ ion is liberated, the negative charge on oxygen is reduced a little due to withdrawing effect of nitro group. The near the group, more is the inductive effect. Hence, nitro group on ortho position has higher inductive effect compared to the nitro group on para position. The stability of the anion formed after liberation of H+ is directly proportional to the acidity of a compound.
Hence, due to these 2 reasons, o-nitrobenzoic acid is more acidic compared to p-nitrobenzoic acid.
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The nitro group (NO2) is always electron withdrawing either by resonance (ortho or para position) or induction (ortho or meta positions) and will stabilize formation of the carboxylate and H+. Both factors (resonance and induction) contribute in the ortho position while only resonance in the para position so the ortho derivative will be a stronger acid relative to the para. Also, since resonance effects are greater than inductive when comparing the meta and para positions, this consideration will put the order of acidity, from strongest to weakest, as
ortho > para > meta.
So, what are the numbers?
ortho-nitrobenzoic acid pKa = 2.16
para-nitrobenzoic acid pKa = 3.41
meta-nitrobenzoic acid pKa - 3.47
So, my prediction is correct though para/meta are pretty close.
The nitro group (NO2) is always electron withdrawing either by resonance (ortho or para position) or induction (ortho or meta positions) and will stabilize formation of the carboxylate and H+. Both factors (resonance and induction) contribute in the ortho position while only resonance in the para position so the ortho derivative will be a stronger acid relative to the para. Also, since resonance effects are greater than inductive when comparing the meta and para positions, this consideration will put the order of acidity, from strongest to weakest, as
ortho > para > meta.
So, what are the numbers?
ortho-nitrobenzoic acid pKa = 2.16
para-nitrobenzoic acid pKa = 3.41
meta-nitrobenzoic acid pKa - 3.47
So, my prediction is correct though para/meta are pretty close.
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