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Why is 2-hydroxybenzoic acid more acidic than 4-hydroxybenzoic acid?
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Leon Rogers
Why is 2-hydroxybenzoic acid more acidic than 4-hydroxybenzoic acid?
Two reasons; minor: OH has a negative inductive effect (electron withdrawing) which is in ortho-position is stronger as compared with that in para-position; major: the ortho-OH can stabilize the COO- via hydrogen bond (six-membered ring).
Two reasons; minor: OH has a negative inductive effect (electron withdrawing) which is in ortho-position is stronger as compared with that in para-position; major: the ortho-OH can stabilize the COO- via hydrogen bond (six-membered ring).
Anything that withdraws electrons from the -COOH group will tend to make a carboxylic acid more acid, because it makes it easier for the proton to leave as an H+ ion.
In this case, the fact that there is an oxygen atom (in the hydroxy group right next to the acid moiety) results in a greater pull on the electrons near the hydrogen than what we see when that oxygen is all the way on the other side of the benzene ring. This makes for easier deprotonation and greater acidity.
Anything that withdraws electrons from the -COOH group will tend to make a carboxylic acid more acid, because it makes it easier for the proton to leave as an H+ ion.
In this case, the fact that there is an oxygen atom (in the hydroxy group right next to the acid moiety) results in a greater pull on the electrons near the hydrogen than what we see when that oxygen is all the way on the other side of the benzene ring. This makes for easier deprotonation and greater acidity.
In salicyclic acid there is intramolecular attraction due less distance between the hydrogen of -OH group and the oxygen of -COOH group , while in para and meta benzoic acid there is compairtivly more intermolecular attraction then the intra molecular attraction . So salicyclic acid have a lower melting point .
In salicyclic acid there is intramolecular attraction due less distance between the hydrogen of -OH group and the oxygen of -COOH group , while in para and meta benzoic acid there is compairtivly more intermolecular attraction then the intra molecular attraction . So salicyclic acid have a lower melting point .
I got fancy and drew you a ball and stick 3D model. The OH in 2-hydroxybenzoate stabilizes the anion of the carboxylate by H bonding, thus increasing the acidity. 4-hydroxybenzoate has no such H bond stabilizing the carboxylate.
I got fancy and drew you a ball and stick 3D model. The OH in 2-hydroxybenzoate stabilizes the anion of the carboxylate by H bonding, thus increasing the acidity. 4-hydroxybenzoate has no such H bond stabilizing the carboxylate.
Ortho-hydroxybenzoic acid is more acidic than benzoic acid ....its not due to orthoeffect ,main reason behind it is extra stablisation of product due to intramolecular hydrogen bonding after losing proton
Ortho-hydroxybenzoic acid is more acidic than benzoic acid ....its not due to orthoeffect ,main reason behind it is extra stablisation of product due to intramolecular hydrogen bonding after losing proton
I’m going to disagree with Marcos Duran. I think ortho-hydroxybenzoic acid would be more stable, because of a hydrogen bond between the hydroxy H atom and one of the carboxyl O atoms.
I’m going to disagree with Marcos Duran. I think ortho-hydroxybenzoic acid would be more stable, because of a hydrogen bond between the hydroxy H atom and one of the carboxyl O atoms.
In case of 2-hydroxybenzoic acid, the OH group is on the ortho-position. In the case of 4-hydroxybenzoic acid, the OH group is on the para-position. Now, here the concept of electron withdrawing is not the only factor. Instead, the formation of internal hydrogen bonding is the reason.
In case of 2-hydroxybenzoic acid, the OH group is on the ortho-position. In the case of 4-hydroxybenzoic acid, the OH group is on the para-position. Now, here the concept of electron withdrawing is not the only factor. Instead, the formation of internal hydrogen bonding is the reason.
Two reasons; minor: OH has a negative inductive effect (electron withdrawing) which is in ortho-position is stronger as compared with that in para-position; major: the ortho-OH can stabilize the COO- via hydrogen bond (six-membered ring).
Two reasons; minor: OH has a negative inductive effect (electron withdrawing) which is in ortho-position is stronger as compared with that in para-position; major: the ortho-OH can stabilize the COO- via hydrogen bond (six-membered ring).
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Anything that withdraws electrons from the -COOH group will tend to make a carboxylic acid more acid, because it makes it easier for the proton to leave as an H+ ion.
In this case, the fact that there is an oxygen atom (in the hydroxy group right next to the acid moiety) results in a greater pull on the electrons near the hydrogen than what we see when that oxygen is all the way on the other side of the benzene ring. This makes for easier deprotonation and greater acidity.
Anything that withdraws electrons from the -COOH group will tend to make a carboxylic acid more acid, because it makes it easier for the proton to leave as an H+ ion.
In this case, the fact that there is an oxygen atom (in the hydroxy group right next to the acid moiety) results in a greater pull on the electrons near the hydrogen than what we see when that oxygen is all the way on the other side of the benzene ring. This makes for easier deprotonation and greater acidity.
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In salicyclic acid there is intramolecular attraction due less distance between the hydrogen of -OH group and the oxygen of -COOH group , while in para and meta benzoic acid there is compairtivly more intermolecular attraction then the intra molecular attraction . So salicyclic acid have a lower melting point .
In salicyclic acid there is intramolecular attraction due less distance between the hydrogen of -OH group and the oxygen of -COOH group , while in para and meta benzoic acid there is compairtivly more intermolecular attraction then the intra molecular attraction . So salicyclic acid have a lower melting point .
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I got fancy and drew you a ball and stick 3D model. The OH in 2-hydroxybenzoate stabilizes the anion of the carboxylate by H bonding, thus increasing the acidity. 4-hydroxybenzoate has no such H bond stabilizing the carboxylate.
I got fancy and drew you a ball and stick 3D model. The OH in 2-hydroxybenzoate stabilizes the anion of the carboxylate by H bonding, thus increasing the acidity. 4-hydroxybenzoate has no such H bond stabilizing the carboxylate.
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Ortho-hydroxybenzoic acid is more acidic than benzoic acid ....its not due to orthoeffect ,main reason behind it is extra stablisation of product due to intramolecular hydrogen bonding after losing proton
Ortho-hydroxybenzoic acid is more acidic than benzoic acid ....its not due to orthoeffect ,main reason behind it is extra stablisation of product due to intramolecular hydrogen bonding after losing proton
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It’s not and wouldn’t be expected to be more acidic.
The former is:
It’s not and wouldn’t be expected to be more acidic.
The former is:
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I’m going to disagree with Marcos Duran. I think ortho-hydroxybenzoic acid would be more stable, because of a hydrogen bond between the hydroxy H atom and one of the carboxyl O atoms.
But let’s see what NIST Webbook says:
o-hydroxybenzoic acid: ΔfH°(gas) = -495.8 ± 1.4 ← ~3 kJ/mol more stable
p-hydroxybenzoic acid: ΔfH°(gas) = -492.6 ± 2.2
I’m going to disagree with Marcos Duran. I think ortho-hydroxybenzoic acid would be more stable, because of a hydrogen bond between the hydroxy H atom and one of the carboxyl O atoms.
But let’s see what NIST Webbook says:
o-hydroxybenzoic acid: ΔfH°(gas) = -495.8 ± 1.4 ← ~3 kJ/mol more stable
p-hydroxybenzoic acid: ΔfH°(gas) = -492.6 ± 2.2
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In case of 2-hydroxybenzoic acid, the OH group is on the ortho-position. In the case of 4-hydroxybenzoic acid, the OH group is on the para-position. Now, here the concept of electron withdrawing is not the only factor. Instead, the formation of internal hydrogen bonding is the reason.
In case of 2-hydroxybenzoic acid, the OH group is on the ortho-position. In the case of 4-hydroxybenzoic acid, the OH group is on the para-position. Now, here the concept of electron withdrawing is not the only factor. Instead, the formation of internal hydrogen bonding is the reason.
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