DAT Bootcamp o chem test 1 #3

[myshinyteethandme]

hey guys! if anyone has bootcamp and can take a look at this question for me it would be great since I cant post a pic of the molecule. I want to know why the ph groups change to trans in the answer. thanks!

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[TheEpicFruitCake]

Look at the explanation. "E2 elimination, the leaving group (Br) and the ß-hydrogen must be antiperiplanar"

If you don't understand: http://lmgtfy.com/?q=E2+antiperiplanar

 

[myshinyteethandme]

Look at the explanation. "E2 elimination, the leaving group (Br) and the ß-hydrogen must be antiperiplanar"

If you don't understand: http://lmgtfy.com/?q=E2 antiperiplanar

I understand that the leaving group and the B-hydrogen must be antiperiplanar but i dont see how thats affecting the Ph group

 

[LightAtTheEnd]

Antiperiplanar means that the Br and leaving H must be pointing 180 degrees to each other + most stable alkene formed (if possible).

The way the molecule is arranged does not show H being 180 degrees to the Br.

So you need to rotate the carbon on the left until CH3 is on the wedge, Phenyl group is on the dash, and H is pointing down. After the H is abstracted, right Phenyl will be on the dash and the left one will be on the wedge = trans.

 

[TheEpicFruitCake]

A model set might be helpful if you can't "see it" in your head.

If you don't have one just use your fingers. pointer, middle, ring and make an imaginary equilateral triangle. Label each one with a maker. Lets make hydrogen red (pointer) for funzies, carbon blue (middle), Ph nothing

now put them like the picture your hand will be upside down at this point with your palm facing up hahaha. Now make the red finger point down (since you want it antiperiplaner to Br which is straight up). If you still can't see it idk what else to do lol