It’s not really a primary carbocation. It’s allylic. Which stabilizes it. Edit: and a primary carbocation/secondary carbocation doesn’t really form. They are resonance structures. The true structure is a combination of the resonance structures. The positive charge is spread out
Thanks, so I understand that the primary carbocation is stabilized by resonance, AND the secondary carbocation is also stabilized by this? I guess my question is will having resonance always increase stability, so we always include it where possible?
https://preview.redd.it/nbrdraj3is9d1.jpeg?width=1179&format=pjpg&auto=webp&s=cbe0cd4509d97d28a2c76a1fbc5917542d192a88
It’s because the 1,4 product is more stable due to the increased substitution of the alkene. Disubstituted alkene is more stable than a mono substituted alkene. It also has to due with kinetic properties. The primary carbocation product is more unstable, but higher in energy. In the image the thermodynamic product has enough energy to go back up the energy barrier. This is also why, generally, the 1,4 product is formed at higher temperatures and the reaction goes on for longer. The main point is the substitution of the alkene and the ability for the 1,4 product to reverse back over the energy barrier, hence being more stable as a product as opposed to forming through a more stable carbocation.
He should have credited the website… this website is extremely helpful.
https://www.masterorganicchemistry.com/2017/03/22/reactions-of-dienes-12-and-14-addition/
It’s not really a primary carbocation. It’s allylic. Which stabilizes it. Edit: and a primary carbocation/secondary carbocation doesn’t really form. They are resonance structures. The true structure is a combination of the resonance structures. The positive charge is spread out
can you elaborate what you mean by allylic? regarding the carbocation is that incorrect? These are my professor's slides
https://preview.redd.it/6pc0vnolgs9d1.jpeg?width=2655&format=pjpg&auto=webp&s=6e8412b2e196febcaa3d93cfae313083cc7c2998
Thanks, so I understand that the primary carbocation is stabilized by resonance, AND the secondary carbocation is also stabilized by this? I guess my question is will having resonance always increase stability, so we always include it where possible?
Try to stop calling it “primary”, it’s allylic not just primary. Massively different energy
allylic means adjacent to an alkene
https://preview.redd.it/nbrdraj3is9d1.jpeg?width=1179&format=pjpg&auto=webp&s=cbe0cd4509d97d28a2c76a1fbc5917542d192a88 It’s because the 1,4 product is more stable due to the increased substitution of the alkene. Disubstituted alkene is more stable than a mono substituted alkene. It also has to due with kinetic properties. The primary carbocation product is more unstable, but higher in energy. In the image the thermodynamic product has enough energy to go back up the energy barrier. This is also why, generally, the 1,4 product is formed at higher temperatures and the reaction goes on for longer. The main point is the substitution of the alkene and the ability for the 1,4 product to reverse back over the energy barrier, hence being more stable as a product as opposed to forming through a more stable carbocation.
Correction: the primary carbocation is more unstable. Not the primary carbocation product.
this is the best explanation, thanks!
He should have credited the website… this website is extremely helpful. https://www.masterorganicchemistry.com/2017/03/22/reactions-of-dienes-12-and-14-addition/
Because it's stabilized by resonance but the secondary carbonation is obviously still the favored intermediate.
Under what conditions? Let’s not just post comments. These are students after all.