When to obey zaitsevs rule?

[Seenary]

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Hey guys,
Does an E2 with a strong hindered base result in the least substituded double bond on a 2 degree alkyl halide? This is what destroyer claims. then when do we get the most subs?

 

[alanan84]

Hey guys,
Does an E2 with a strong hindered base result in the least substituded double bond on a 2 degree alkyl halide? This is what destroyer claims. then when do we get the most subs?

Destroyer is correct, a strong hindered base gives you the less substituted alkene because that hindrance keeps it from getting in and attacking the more substituted location. That means you will get the zaitsev product with an unhindered base.

 

[Seenary]

thanks for the clarification

 

[BiomajorPreDent]

So normally you get Zaitsevs rule in E2 unless its a hindered base, then you get hoffman

Does this only apply to E2 or does it also apply to E1 as well?

 

[BiomajorPreDent]

bump anyone? 😕

 

[Shinpe]

E2 goes through a concerted one-step mechanism. The base attackes the hydrogen at the same time that the leaving group leaves. A more hindered base would attack the most accessible hydrogen, leading usually to less stable (substituted) product, while the less hindered base could attack the more hindered hydrogen, leading to the more stable (subs) product.

E1 goes through a carbocation intermediate and will give the more stable product corresponding to the more stable carbocation, keeping in mind that carbocation shifts can occur too.