# Does the hydrogen taken in an E1 reaction have to be antiperiplanar?

I'm wondering if the hydrogen stolen during an $E_1$ reaction has to be antiperiplanar/anticoplanar like the hydrogen in an $E_2$ reaction.

Intuitively I'd say no, because the carbocation is flat so there's less steric hindrance than an E2 reaction, but I want to check.

As an example, we could use 3-methyl-2-bromobutane. Once that carbocation forms and shifts, does it matter which hydrogen is stolen?

It actually does not matter whether or not it is antiperiplanar, because once the carbocation is formed, there is no sense of antiperiplanar. The two carbon atoms are in the same plane now. For a planar carbocation, all arrangements are equivalent(i.e. no sense of stereoisomerism). It does not matter which side the base attacks on. Also, since the bond angle in an $sp^2$ system is greater than that of an $sp^3$ system, the steric resistance to the base is less, which is the point you mentioned.
• Yes, you're right. I should not have written $\alpha-\beta$ Dec 9, 2014 at 9:01