E2 and bulky base

[FeinMS]

It seems like there's a little discrepancy between MCAT's approach about E2 and how I learned in my ochem classes. That I want to clear up.

In my class, E2 could be done with bulky or non-bulky bases. Non-bulky base would yield Zaitsev product by eliminating more hindered hydrogen leading to more stable alkene whereas bulky base would yield Hoffman product by eliminating less hindered hydrogen leading to less stable alkene.

In TBR's discussion of E2, they say E2 uses bulky bases to limit the amount of SN2 product, and it seems like most of MCAT'ers agree with this. Does this mean that I should always go for the Hoffman product?

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[Life Eternal]

If you have non bulky strong base you can have sn2 with a primary alkyl halide(you will get E2 with secondary and tertiary). If you use a bulky base you will always have E2.

 

[FeinMS]

Thanks, but that's not the question I'm asking...

 

[Life Eternal]

hoffman rule comes into play when you have a bulky base and a tertiary alkyl halide

 

[mehc012]

hoffman rule comes into play when you have a bulky base and a tertiary alkyl halide

Still not OP's question, though...

 

[FeinMS]

Kinda gave up... lol

 

[mehc012]

Kinda gave up... lol

I would spiel what I know, but what you're asking is more "what does the MCAT want" rather than "I need an explanation"...and as I've said, I haven't started MCAT prep yet 😳

Personally, if it's not a BBB, I start worrying about substitution, so on exams I've usually seen either a BBB or a straight-up substitution question, and very rarely that grey area which you're discussing. I would hope the MCAT would be similar, but as I said, I don't know.

 

[FeinMS]

Ok then, it seems like "since E2 usually involves BBB, the product is usually Hoffman." Thanks.