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The pyridine/benzene stability 'paradox'?
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+ Resonance
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Mark Roberts
The pyridine/benzene stability 'paradox'?
When you think about stability, think of it as a relative value, meaning in comparison to atoms of other elements. Therefore, pyridine is more stable than the benzene but less stable than other elements, in general.
You are correct when you say stability is inversely proportional to reactivity. But because stability is relative, it is very difficult to comment on the relative reactivity.
EDIT
Heat of hydrogenation of an alkene in which the double bonds are conjugated is not additive because such an alkene is resonance stabilized, and, therefore, its Lewis structure, which the calculation would be based on, is a poor representation of the molecule.
I have found 2 aspects :
Pyridine is less reactive, than benzene toward electrophilic aromatic
substitution, because nitrogen is more electronegative, than carbon and acts like an
electron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is more reactive than benzene because the presence of nitrogen
enables pyridine to react with nucleophiles. Nitrogen is an electron withdrawing
substituents enables the aromatic ring to participate in such reactions and the
substitution happens in the ortho and meta positions.
When you think about stability, think of it as a relative value, meaning in comparison to atoms of other elements. Therefore, pyridine is more stable than the benzene but less stable than other elements, in general.
You are correct when you say stability is inversely proportional to reactivity. But because stability is relative, it is very difficult to comment on the relative reactivity.
EDIT
Heat of hydrogenation of an alkene in which the double bonds are conjugated is not additive because such an alkene is resonance stabilized, and, therefore, its Lewis structure, which the calculation would be based on, is a poor representation of the molecule.
I have found 2 aspects :
Pyridine is less reactive, than benzene toward electrophilic aromaticsubstitution, because nitrogen is more electronegative, than carbon and acts like anelectron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is more reactive than benzene because the presence of nitrogenenables pyridine to react with nucleophiles. Nitrogen is an electron withdrawingsubstituents enables the aromatic ring to participate in such reactions and thesubstitution happens in the ortho and meta positions.
Fair, thats true in most cases maybe, but for C=C bonds you can measure the energy stored within them using heats of hydrogenation. Im really just focused on organic compounds (and in this case two resonant, aromatic compounds), and for them I thought stability could be objectively ranked based on the energy content of the bonds?More
Surely its reactivity thats relative rather than stability? Theres an objective measurement for stability (correct me if Im wrong) - heats of hydrogenation, right? Reactivity is relative seeing as one molecule may be more prone to react than another due to factors like lone pairs, etc.More
When you think about stability, think of it as a relative value, meaning in comparison to atoms of other elements. Therefore, pyridine is more stable than the benzene but less stable than other elements, in general.
You are correct when you say stability is inversely proportional to reactivity. But because stability is relative, it is very difficult to comment on the relative reactivity.
EDIT
Heat of hydrogenation of an alkene in which the double bonds are conjugated is not additive because such an alkene is resonance stabilized, and, therefore, its Lewis structure, which the calculation would be based on, is a poor representation of the molecule.
I have found 2 aspects :
Pyridine is less reactive, than benzene toward electrophilic aromatic substitution, because nitrogen is more electronegative, than carbon and acts like an electron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is more reactive than benzene because the presence of nitrogen enables pyridine to react with nucleophiles. Nitrogen is an electron withdrawing substituents enables the aromatic ring to participate in such reactions and the substitution happens in the ortho and meta positions.
When you think about stability, think of it as a relative value, meaning in comparison to atoms of other elements. Therefore, pyridine is more stable than the benzene but less stable than other elements, in general.
You are correct when you say stability is inversely proportional to reactivity. But because stability is relative, it is very difficult to comment on the relative reactivity.
EDIT
Heat of hydrogenation of an alkene in which the double bonds are conjugated is not additive because such an alkene is resonance stabilized, and, therefore, its Lewis structure, which the calculation would be based on, is a poor representation of the molecule.
I have found 2 aspects :
Pyridine is less reactive, than benzene toward electrophilic aromaticsubstitution, because nitrogen is more electronegative, than carbon and acts like anelectron withdrawing group. As a result, the meta hydrogen is substituted.
Pyridine is more reactive than benzene because the presence of nitrogenenables pyridine to react with nucleophiles. Nitrogen is an electron withdrawingsubstituents enables the aromatic ring to participate in such reactions and thesubstitution happens in the ortho and meta positions.
More
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