Destroyer - Organic # 16

[busupshot83]

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I understand that stability of radicals is as follows:

primary < secondary < tertiary < allylic

What I don't understand in this problem is how answer (E) is more stable than answer (B). The way I see it...

(E) is tertiary allyl
(B) is tertiary allyl

However, the solutions say that (B) is tertiary vinylic. What is the difference between allylic and vinylic?

 

[jfitzpat]

I understand that stability of radicals is as follows:

primary < secondary < tertiary < allylic

What I don't understand in this problem is how answer (E) is more stable than answer (B). The way I see it...

(E) is tertiary allyl
(B) is tertiary allyl

However, the solutions say that (B) is tertiary vinylic. What is the difference between allylic and vinylic?

I am pretty sure it is because choice E is resonance stabilized by the pi bond (allylic). Since there is no way to configure a resonance stabilization of B, it would be less stable than answer E.

 

[BodybldgDoc]

a vinyl group is R-CH=CH2 whereas an allyl group is CH2=CH-CH2-R and as you can see an allyl group can delocalize its Pi electrons which makes it more stable as opposed to a vinyl group which is why the answer would be E

 

[DentalKitty]

I understand that stability of radicals is as follows:

primary < secondary < tertiary < allylic

What I don't understand in this problem is how answer (E) is more stable than answer (B). The way I see it...

(E) is tertiary allyl
(B) is tertiary allyl

However, the solutions say that (B) is tertiary vinylic. What is the difference between allylic and vinylic?

Vinylic is when the + charge is on a C that has the double bond. Allylic is when the + charge is on a C next to a C with a double bond. Like mentioned above, when you have allylic it is similar to conjugated double bonds where the pi electrons can delocalize and form resonance structures which stabilizes the cation. With vinylic, the charge cannot be delocalized so it is less stable. Not having the ability to delocalize has to do with the orientation of the orbitals and them not being in the same plane. Hope this helps!