Is there a requirement for the stereochemistry of the starting material in E1 reactions? Why?

Jan 11, 2015

There is no stereochemical requirement for the starting material in $E 1$ reactions.

An $E 2$ elimination does have a stereochemistry requirement: the β hydrogen and the leaving group must be antiperiplanar to each other.

This causes formation of the less stable alkene in cyclohexane compounds such as ($1 R , 2 R$)-1-bromo-1,2-dimethylcyclohexane.

This requirement does not exist in $E 1$ eliminations, because the leaving group leaves first, forming a carbocation.

The β C-H bond must be able to overlap the p orbital of the carbocation , so the β C-H bond must be axial.

We can always do a ring flip, so we can always form the more stable product, 1,2-dimethylcyclohexane.