[Strike]

I'll ask the question in this picture because it includes various structures of different compounds so it was just easier to put everything into this image.



I think this is an example of a Dehydrohalogenation of Alkyl Halides so the hydrogen and halide group have to be "anti", correct? Well in both, the Cl could be anti to any of the Hydrogens adjacent to it (where the double-bond forms), so I don't know why when the Cl is flipped, the reaction is slower and only gives the less stable product.

My only explanation is when the Cl is pointing up, the EtO-/EtOH cannot reach the Cl from the bottom because the CH(CH3)2 takes up so much space. But then it could just attack from the top and kick the Cl out.

Thanks in advance!

[azmanam]

start by drawing chair structures of both chloride starting materials AND both of the chair flips.

post your results here

[Strike]

These are the chair conformations.

For the second structures, why wouldn't it be able to form a double-bond between the Cl and isopropyl group?

[orgopete]

E2 elimination reactions are like SN2 reactions in that the electrons of an elimination must come from the opposite side of the departing chloride. This is usually explained with the term antiperiplanar.

[azmanam]

yes, you need the anti-periplanar relationship between the departing chloride and the beta-proton (the proton being removed by the base.  This means the dihedral angle between the chloride and the proton on the beta carbon atom must be 180^o.  Draw your chair structures again, and circle all the protons on beta carbon atoms which have a 180^o dihedral angle with the chloride.

[Strike]

Ah!!

I totally get it. The base can only react with the Hydrogens that are "anti" on the hexane ring which only gives the less stable product. As for a slower reaction, is it because there is only one place for the base to react as well as the product being less stable so it requires more energy to strip the Cl off?

[azmanam]

...not quite.

look at your 2 chair structure/chair flip pairs again.  We know chair structures and their chair flips are in equilibrium - that is, the two chair flips are interconverting.  Circle the chair structure in each pair that is more stable at equilibrium.  How does this compare with the chair structures that have the hydrogen atoms at 180^o dihedral angle?