Quick Orgo-related question: WHY is it that 1,2-addition to a conjugated diene tends to take place in a lower temperature and under kinetic control while 1,4-addition takes place at higher temperatures under thermodynamic control? I was just curious. My guess is that 1,2-addition takes place at lower temperatures because it takes less energy to add across the 1st and 2nd atoms in a pi-bond network.
1,2 and 1,4 Addition to a Conjugated Diene
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Activation energy.
The thermodynamic form (1,2) is favored at lower temperatures because the activation energy for the kinetic form (1,4) is too high.
Likewise, at higher temperatures the kinetic form is favored because it happens considerably faster and there is enough energy to activate it.
The thermodynamic form (1,2) is favored at lower temperatures because the activation energy for the kinetic form (1,4) is too high.
Likewise, at higher temperatures the kinetic form is favored because it happens considerably faster and there is enough energy to activate it.
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Pretty sure.
1,2 addition is called 'thermodynamic' because it is the most stable form of the intermediate. Consequently, it also means less activation energy (read less temperature) is needed for the molecules to have the proper configuration in order for the reaction to occur. Which is why it is favored at lower temperatures.
By contrast, the 1,4 addition is called 'kinetic' because it is more kinetically favorable (read rxn occurs faster). However, the intermediate is less stable which means that more energy (a higher temperature) is required for the molecules to have the proper intermediate form. But if it can reach it the end product is more stable and the reaction occurs faster which makes it favorable.
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Just re-read that and realized I made a mistake.
It turns out that the kinetic (1,2) is favored at the low temperature because it has the lower activation energy while thermodynamic (1,4) is favored at higher temperatures because it has a higher activation energy but an ultimately more stable product.
Sorry 'bout that. ^^
It turns out that the kinetic (1,2) is favored at the low temperature because it has the lower activation energy while thermodynamic (1,4) is favored at higher temperatures because it has a higher activation energy but an ultimately more stable product.
Sorry 'bout that. ^^
Last edited:
Just re-read that and realized I made a mistake.
It turns out that the kinetic (1,2) is favored at the low temperature because it has the lower activation energy while thermodynamic (1,4) is favored at higher temperatures because it has a higher activation energy but an ultimately more stable product.
Sorry 'bout that. ^^
It's okay! That is a good diagram. Thank you for sharing that!
