Anti-periplanar question

[Piepiesuperpie]

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Can someone explain this to me? I drew the most stable conformation (anti with the CH3s 180 from each other) and the Br and the beta hydrogen were perfectly 180, so I thought that it E2 would produce the major product.

 

[FeralisExtremum]

The question asks what best describes THIS structure in the specifically shown conformation though, so you shouldn't actually be rotating it, but evaluating it as is. It's the least stable because in the shown conformation, the bulky groups are not positioned anti (in fact they are gauche, in a Newman projection).

What I don't get is why this leads to the minor product, because I don't see how a minor product can even form. There's only one carbon with beta hydrogens attached, so there's only one possible E2 product here regardless.

 

[Piepiesuperpie]

Haha, wow, totally missed that.

As for the minor product, even though it's the same product at the end, the mechanism of using the less stable conformation then producing the product happens less often than reactant --> (most stable conformation) --> product. Although the product is the same, the way the reaction proceeds is slightly different.

 

[FeralisExtremum]

Wow, that's confusing. They should have just said "proceeds via less stable intermediate" instead of using the word product.