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Why is pyrrole more reactive than pyridine for an electrophilic substitution reaction?
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Kasturi Khatun
Why is pyrrole more reactive than pyridine for an electrophilic substitution reaction?
Pyrrolidine is more basic than pyridine. The pKa of pyrrolidinium cation is 11.3, and that of pyridinium cation is 5.3; i.e., the former cation (conjugate acid) is more acidic than the latter. This fact has something to do with the molecular electronic structures of both compounds. (Pyrrolidine is aliphatic, roughly sp3, while pyridine is aromatic, roughly sp2.)
Pyrrolidine is more basic than pyridine. The pKa of pyrrolidinium cation is 11.3, and that of pyridinium cation is 5.3; i.e., the former cation (conjugate acid) is more acidic than the latter. This fact has something to do with the molecular electronic structures of both compounds. (Pyrrolidine is aliphatic, roughly sp3, while pyridine is aromatic, roughly sp2.)
Acetanilide had an amide attached to the benzene ring, while aniline has a amine attached. Amines are more electron donating than amides. Hence Acetanilide is less active than aniline.
Acetanilide had an amide attached to the benzene ring, while aniline has a amine attached. Amines are more electron donating than amides. Hence Acetanilide is less active than aniline.
I think I now what your problem is.You probably think that Ethyl group has greater +I effect than Methyl group,therefore Ethyl Benzene is more electron rich and therefore more reactive than Methyl Benzene.But you must also take into account the hyper-conjugation effect of the alkyl substituents,and also take into account that Hyperconjugation effect dominates over Inductive effect. Ethyl group has 2 alpha hydrogens while Methyl group has 3 alpha hydrogens,therefore Hyperconjugation effect of Methyl group dominates over Ethyl group and overall Methyl Benzene is more reactive.
I think I now what your problem is.You probably think that Ethyl group has greater +I effect than Methyl group,therefore Ethyl Benzene is more electron rich and therefore more reactive than Methyl Benzene.But you must also take into account the hyper-conjugation effect of the alkyl substituents,and also take into account that Hyperconjugation effect dominates over Inductive effect. Ethyl group has 2 alpha hydrogens while Methyl group has 3 alpha hydrogens,therefore Hyperconjugation effect of Methyl group dominates over Ethyl group and overall Methyl Benzene is more reactive.
Pyridine is less reactive, than benzene toward electrophilic aromatic substitution, because nitrogen is moreelectronegative, than carbon and acts like an electron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is less reactive, than benzene toward electrophilic aromatic substitution, because nitrogen is moreelectronegative, than carbon and acts like an electron withdrawing group. As a result, the meta hydrogen is substituted.
The effect of a halogen on electrophilic aromatic substitution is somewhat complicated. The halogen is a slight pi electron donor but a significant sigma electron withdrawer. The result of the electron withdrawing action is that the halogenated arene reacts more slowly than unsubstituted benzene. On the other hand, the pi electron donation is what determines the preferred location of the electrophilic substitution. Because of this, the halogen is an ortho/para director.
The effect of a halogen on electrophilic aromatic substitution is somewhat complicated. The halogen is a slight pi electron donor but a significant sigma electron withdrawer. The result of the electron withdrawing action is that the halogenated arene reacts more slowly than unsubstituted benzene. On the other hand, the pi electron donation is what determines the preferred location of the electrophilic substitution. Because of this, the halogen is an ortho/para director.
Pyrrolidine is more basic than pyridine. The pKa of pyrrolidinium cation is 11.3, and that of pyridinium cation is 5.3; i.e., the former cation (conjugate acid) is more acidic than the latter. This fact has something to do with the molecular electronic structures of both compounds. (Pyrrolidine is aliphatic, roughly sp3, while pyridine is aromatic, roughly sp2.)
Pyrrolidine is more basic than pyridine. The pKa of pyrrolidinium cation is 11.3, and that of pyridinium cation is 5.3; i.e., the former cation (conjugate acid) is more acidic than the latter. This fact has something to do with the molecular electronic structures of both compounds. (Pyrrolidine is aliphatic, roughly sp3, while pyridine is aromatic, roughly sp2.)
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Acetanilide had an amide attached to the benzene ring, while aniline has a amine attached. Amines are more electron donating than amides. Hence Acetanilide is less active than aniline.
Acetanilide had an amide attached to the benzene ring, while aniline has a amine attached. Amines are more electron donating than amides. Hence Acetanilide is less active than aniline.
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I think I now what your problem is.You probably think that Ethyl group has greater +I effect than Methyl group,therefore Ethyl Benzene is more electron rich and therefore more reactive than Methyl Benzene.But you must also take into account the hyper-conjugation effect of the alkyl substituents,and also take into account that Hyperconjugation effect dominates over Inductive effect. Ethyl group has 2 alpha hydrogens while Methyl group has 3 alpha hydrogens,therefore Hyperconjugation effect of Methyl group dominates over Ethyl group and overall Methyl Benzene is more reactive.
I think I now what your problem is.You probably think that Ethyl group has greater +I effect than Methyl group,therefore Ethyl Benzene is more electron rich and therefore more reactive than Methyl Benzene.But you must also take into account the hyper-conjugation effect of the alkyl substituents,and also take into account that Hyperconjugation effect dominates over Inductive effect. Ethyl group has 2 alpha hydrogens while Methyl group has 3 alpha hydrogens,therefore Hyperconjugation effect of Methyl group dominates over Ethyl group and overall Methyl Benzene is more reactive.
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Pyridine is less reactive, than benzene toward electrophilic aromatic substitution, because nitrogen is moreelectronegative, than carbon and acts like an electron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is less reactive, than benzene toward electrophilic aromatic substitution, because nitrogen is moreelectronegative, than carbon and acts like an electron withdrawing group. As a result, the meta hydrogen is substituted.
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The effect of a halogen on electrophilic aromatic substitution is somewhat complicated. The halogen is a slight pi electron donor but a significant sigma electron withdrawer. The result of the electron withdrawing action is that the halogenated arene reacts more slowly than unsubstituted benzene. On the other hand, the pi electron donation is what determines the preferred location of the electrophilic substitution. Because of this, the halogen is an ortho/para director.
The effect of a halogen on electrophilic aromatic substitution is somewhat complicated. The halogen is a slight pi electron donor but a significant sigma electron withdrawer. The result of the electron withdrawing action is that the halogenated arene reacts more slowly than unsubstituted benzene. On the other hand, the pi electron donation is what determines the preferred location of the electrophilic substitution. Because of this, the halogen is an ortho/para director.
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