[OrdinaryDay]

Treatment of cis-1,1-bromo-4(1,1-dimethyethyl)-cyclohexane with a strong base leads to rapid bimolecular elimination and gives a corresponding alkene. In the book it says that the 2 hydrogens are located anti to the axial bromine substituent. Their geometry is very similar to that required by the E2 transition state and so elimination would consequently be easier.

I need to understand these two assumptions more clearly. How is it known that the two hydrogens in the cis form are located anti to the bromine substitutent? And what geometry specifically is favorable for the E2 transition state?

If possible, can you also answer this question, its been bothering me lately. Does the numbering of the carbons matter for molecules like 3,3-dibromocyclohexanol? Wouldn't it just be the same everywhere? Thanks

[sjb]

What is the shape of the cyclohexane ring?

To be completely honest with you, I'm a bit confused by the use of cis here to describe the molecule, as I can only picture one diasteromer as it is 1,1-disubstituted (identically)

The numbering problem, is probably more simple, as I don't believe the numbering is the same everywhere. Try drawing out your compound and numbering it different ways, only one is right (but to confuse matters this way may change if you have further substitution)

S

[Noah Arkwright]

I'm confused too. How is it cis or trans, the 2 substitutes being identical? Well, I think you answered the first question yourself. If the two hydrogens would be sin, the energy needed to reach the E2 transition state would be too high and the reaction wouldn't take place. At least that's how I see it...

As for the numbering problem, carbon number 1 is the one with the hydroxyl and number 3 the one with the two bromine substituents, labeling them differently would be incorrect from my point of view.

Cheers.