Creating conjugated system with E2

[September24]

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Quick question:

I know with benzylic electrophiles, sometimes E2 creates a hoffman product over even a tertiary subtituted zaitsev product because it creates a conjugated system.

Is this the same for a simple allylic electrophile as well? It creates a conjugated system but not to the extent of a benzylic electrophile.

Simplified question:

Benzylic hydrogen>tertiary hydrogen for E2

However, does Allylic hydrogen>tertiary hydrogen for E2?

Will an allylic hydrogen also favor a hoffman product?

 

[DrknoSDN]

Will an allylic hydrogen also favor a hoffman product?

With benzene your not just talking about adding conjugation but preventing disruption of the benzene conjugation.
A lot of molecules have elimination scenarios where they will eliminate from an unusual position to avoid disrupting the ring. Allylic hydrogens are less likely to be so heavily favored.
I recall that it does occur but the reason it's so common with benzene has more to do with preserving the benzene conjugation vs enhancing it.

Sorry if that response is not helpful. I suppose it's situational.

 

[September24]

It's cool. I think we're on the right track. I guess to simplify the question:

If there was an E2 reaction going on. One created a tertiary (most substituted) alkene. The other product was an "allylic alkene" which would be like c=c-c=c-c (sorry this the best i could do lol).

Allylic alkene. Imagine the first product here except replace the phenyl group with a methyl group:
http://www.organic-chemistry.org/abstracts/lit2/910m.gif