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Activity of different positions in phenol with respect to electrophilic aromatic substitution
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Mary Helsaple
Activity of different positions in phenol with respect to electrophilic aromatic substitution
As the figure below illustrates, substituents on aromatic rings that are electron donating like the methyl and t-butyl groups (and also the hydroxy group [e.g. phenol]) increase the reaction rate at all positions (ortho, meta and para) relative to benzene.
On the other hand, electron withdrawing substituents (the chlorine and ester carbonyl examples) decrease the reaction rate at all positions relative to benzene.
So for phenol, or any other electron donating substituent, while the meta position does react more slowly than the ortho and para positions, it still reacts faster than benzene. Therefore, it would be incorrect to say that the meta position is deactivated. Only when the rate at a given position is less than the rate for a single position in benzene could one say that the position is deactivated.
For future reference a note on terminology. The above figure tells us that nitration of toluene proceeds 24.5 times faster than the nitration of benzene; that is to say that the relative rate for nitration of toluene is 24.5 times greater than benzene. The meta position in toluene reacts 3 times faster than a single position in benzene, this is referred to as the partial rate factor.
As the figure below illustrates, substituents on aromatic rings that are electron donating like the methyl and t-butyl groups (and also the hydroxy group [e.g. phenol]) increase the reaction rate at all positions (ortho, meta and para) relative to benzene.
On the other hand, electron withdrawing substituents (the chlorine and ester carbonyl examples) decrease the reaction rate at all positions relative to benzene.
So for phenol, or any other electron donating substituent, while the meta position does react more slowly than the ortho and para positions, it still reacts faster than benzene. Therefore, it would be incorrect to say that the meta position is deactivated. Only when the rate at a given position is less than the rate for a single position in benzene could one say that the position is deactivated.
For future reference a note on terminology. The above figure tells us that nitration of toluene proceeds 24.5 times faster than the nitration of benzene; that is to say that the relative rate for nitration of toluene is 24.5 times greater than benzene. The meta position in toluene reacts 3 times faster than a single position in benzene, this is referred to as the partial rate factor.
While the hydroxy group increases the electron density via mesomeric effects, wouldnt it decrease the electron density at meta position via inductive effects?More
That is a very good question, and also a very different question from your original question; you might want to ask it as a separate question. Basically, look at your resonance structures. Although the substituent does not interact with the meta position by resonance, it nonetheless stabilizes the overall meta intermediate because a substituent on a double bond stabilizes a double bond. Therefore, the meta intermediate is stabilized compared to the benzene intermediate and will react slightly faster than the benzene case.More
As the figure below illustrates, substituents on aromatic rings that are electron donating like the methyl and t-butyl groups (and also the hydroxy group [e.g. phenol]) increase the reaction rate at all positions (ortho, meta and para) relative to benzene.
On the other hand, electron withdrawing substituents (the chlorine and ester carbonyl examples) decrease the reaction rate at all positions relative to benzene.
So for phenol, or any other electron donating substituent, while the meta position does react more slowly than the ortho and para positions, it still reacts faster than benzene. Therefore, it would be incorrect to say that the meta position is deactivated. Only when the rate at a given position is less than the rate for a single position in benzene could one say that the position is deactivated.
Statement "a" in your question is correct.
(image source)
For future reference a note on terminology. The above figure tells us that nitration of toluene proceeds 24.5 times faster than the nitration of benzene; that is to say that the relative rate for nitration of toluene is 24.5 times greater than benzene. The meta position in toluene reacts 3 times faster than a single position in benzene, this is referred to as the partial rate factor.
As the figure below illustrates, substituents on aromatic rings that are electron donating like the methyl and t-butyl groups (and also the hydroxy group [e.g. phenol]) increase the reaction rate at all positions (ortho, meta and para) relative to benzene.
On the other hand, electron withdrawing substituents (the chlorine and ester carbonyl examples) decrease the reaction rate at all positions relative to benzene.
So for phenol, or any other electron donating substituent, while the meta position does react more slowly than the ortho and para positions, it still reacts faster than benzene. Therefore, it would be incorrect to say that the meta position is deactivated. Only when the rate at a given position is less than the rate for a single position in benzene could one say that the position is deactivated.
Statement "a" in your question is correct.
(image source)
For future reference a note on terminology. The above figure tells us that nitration of toluene proceeds 24.5 times faster than the nitration of benzene; that is to say that the relative rate for nitration of toluene is 24.5 times greater than benzene. The meta position in toluene reacts 3 times faster than a single position in benzene, this is referred to as the partial rate factor.
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