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Why is diene more reactive than alkene?
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+ Resonance
+ Reactivity
+ Stability
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Kevin McKenna
Why is diene more reactive than alkene?
There is a long and elaborate answer by Philipp which will tell you a lot about why — possibly more then you need to know. It boils down to reactiviy meaning easier accessable orbitals meaning a lower LUMO or a higher HOMO in energy terms. Well, going from ethene to butadiene, you go from two π to four and thus you can imagine two additional orbitals to be sandwiched in the middle between the (all)bonding and (all)antibonding ones. This is also shown including an energy scale in Philipp’s answer:
If you liked this answer, please also go and upvote Philipp’s.
There is a long and elaborate answer by Philipp which will tell you a lot about why — possibly more then you need to know. It boils down to reactiviy meaning easier accessable orbitals meaning a lower LUMO or a higher HOMO in energy terms. Well, going from ethene to butadiene, you go from two π to four and thus you can imagine two additional orbitals to be sandwiched in the middle between the (all)bonding and (all)antibonding ones. This is also shown including an energy scale in Philipp’s answer:
If you liked this answer, please also go and upvote Philipp’s.
It is not only the diene itself which is stabilised by resonance, but on electrophilic addition the carbocation formed is also stabilised by resonance if the diene is conjugated. Thus, forming the intermediate for a conjugated diene is easier than forming the intermediate for the alkene, even though the starting compound itself is more stable in case of conjugated dienes and therefore conjugated dienes react faster.
It is not only the diene itself which is stabilised by resonance, but on electrophilic addition the carbocation formed is also stabilised by resonance if the diene is conjugated. Thus, forming the intermediate for a conjugated diene is easier than forming the intermediate for the alkene, even though the starting compound itself is more stable in case of conjugated dienes and therefore conjugated dienes react faster.
The 1,4 addition product is the major product at high temperature, as the actual stability of the product comes into picture rather than the kinetics, which dominates at lower temperature.The 1,4 adduct is thermodynamically stabilised by hyperconjugation.More
Also can you tell how 1,4-addition product is the major product?More
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Conjugated dienes have enhanced stability due to resonance. So they are less reactive when compared to alkenes in general. But many reactions proceed through high-energy cation or free radical intermediates; in these cases the resonance stabilization of the intermediate allyl species makes conjugated dienes much more reactive than alkenes.
As to your other question, a Michael addition is a 1-4 addition, where a nucleophile attacks the β carbon, and produces the thermodynamically favored product, which happens at high temperatures. On the other hand, a 1-2 reaction (on the carbonyl) gives the kinetic product, and is obtained at low temperatures. At higher temperatures, it is not only important that the product forms, but it is also important as to whether the formed product will be stable under the conditions.
Conjugated dienes have enhanced stability due to resonance. So they are less reactive when compared to alkenes in general. But many reactions proceed through high-energy cation or free radical intermediates; in these cases the resonance stabilization of the intermediate allyl species makes conjugated dienes much more reactive than alkenes.
As to your other question, a Michael addition is a 1-4 addition, where a nucleophile attacks the β carbon, and produces the thermodynamically favored product, which happens at high temperatures. On the other hand, a 1-2 reaction (on the carbonyl) gives the kinetic product, and is obtained at low temperatures. At higher temperatures, it is not only important that the product forms, but it is also important as to whether the formed product will be stable under the conditions.
There is a long and elaborate answer by Philipp which will tell you a lot about why — possibly more then you need to know. It boils down to reactiviy meaning easier accessable orbitals meaning a lower LUMO or a higher HOMO in energy terms. Well, going from ethene to butadiene, you go from two π to four and thus you can imagine two additional orbitals to be sandwiched in the middle between the (all)bonding and (all)antibonding ones. This is also shown including an energy scale in Philipp’s answer:
If you liked this answer, please also go and upvote Philipp’s.
There is a long and elaborate answer by Philipp which will tell you a lot about why — possibly more then you need to know. It boils down to reactiviy meaning easier accessable orbitals meaning a lower LUMO or a higher HOMO in energy terms. Well, going from ethene to butadiene, you go from two π to four and thus you can imagine two additional orbitals to be sandwiched in the middle between the (all)bonding and (all)antibonding ones. This is also shown including an energy scale in Philipp’s answer:
If you liked this answer, please also go and upvote Philipp’s.
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It is not only the diene itself which is stabilised by resonance, but on electrophilic addition the carbocation formed is also stabilised by resonance if the diene is conjugated. Thus, forming the intermediate for a conjugated diene is easier than forming the intermediate for the alkene, even though the starting compound itself is more stable in case of conjugated dienes and therefore conjugated dienes react faster.
It is not only the diene itself which is stabilised by resonance, but on electrophilic addition the carbocation formed is also stabilised by resonance if the diene is conjugated. Thus, forming the intermediate for a conjugated diene is easier than forming the intermediate for the alkene, even though the starting compound itself is more stable in case of conjugated dienes and therefore conjugated dienes react faster.
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Conjugated dienes have enhanced stability due to resonance. So they are less reactive when compared to alkenes in general. But many reactions proceed through high-energy cation or free radical intermediates; in these cases the resonance stabilization of the intermediate allyl species makes conjugated dienes much more reactive than alkenes.
As to your other question, a Michael addition is a 1-4 addition, where a nucleophile attacks the β carbon, and produces the thermodynamically favored product, which happens at high temperatures. On the other hand, a 1-2 reaction (on the carbonyl) gives the kinetic product, and is obtained at low temperatures. At higher temperatures, it is not only important that the product forms, but it is also important as to whether the formed product will be stable under the conditions.
Conjugated dienes have enhanced stability due to resonance. So they are less reactive when compared to alkenes in general. But many reactions proceed through high-energy cation or free radical intermediates; in these cases the resonance stabilization of the intermediate allyl species makes conjugated dienes much more reactive than alkenes.
As to your other question, a Michael addition is a 1-4 addition, where a nucleophile attacks the β carbon, and produces the thermodynamically favored product, which happens at high temperatures. On the other hand, a 1-2 reaction (on the carbonyl) gives the kinetic product, and is obtained at low temperatures. At higher temperatures, it is not only important that the product forms, but it is also important as to whether the formed product will be stable under the conditions.
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