Which stereoisomer - cis - or trans-1-bromo-3-tert-butylcyclohexane - will react faster in an E2 elimination reaction? Select the single best answer.

Cis-1-bromo-3-tert-butylcyclohexane will give faster reaction in E2 elimination.

Explanation:

E2 is known as second order reaction. Such reaction take place in a single step. E2 involve breaking of C-H and C-X bond in order to form double bond.

Role of cis geometry:

The base mostly remove hydrogen which is anti-palanar to halogen. So when both group i. e bromide and tert-butyl group will be on one side, (cis), then base can abstract hydrogen easily as a result double bond formation take place so fastly.

The cis molecule will react faster.

Explanation:

In the E2 mechanism, we have to have an anti-peri-planar configuration. The hydrogen that is removed and the leaving group should have a configuration of 90º in an anti position (see the figure red hydrogens).

In the trans configuration the ter-butyl group would exercise a steric hindrance upon the hydrogens that can be removed. In the cis configuration we don't have this problem. Therefore the cis molecule would react faster.