Question

(1R, 2R)-1-chloro-2-methylcyclohexane reacts with potassium ethoxide in ethanol via an E2 mechanism

A. Describe in full detail what you think is happening on the molecular level for this reaction. Be sure to discuss the role of each reactant.

B. Using a molecular level explanation, please explain why this reaction occurs. Be sure to state/discuss why the reactants form form the products shown.

C. Please draw a reaction mechanism for how this reaction occurs including all curved arrows, lone pairs, and formal charges.

D. Construct a reaction coordinate diagram for this reaction. Label axes, starting material(s), intermediate(s), transition state(s), and product(s).

Answer 1

A) The reaction is an example of E2 reaction where a base (ethoxide) attacks an alkyl halide to form an alkene. Potassium ethoxide (EtO^-K⁺) is a strong base and (1R,2R)-1-chloro-2methylcyclohxane is the alkyl halide. Ethanol acts as a solvent in the reaction and helps to stabilize the transition state of E2 elimination.

B) The preferred conformation of the alkyl halide is the conformer (A) as shown below. However, (A) doesn’t have the antiperiplaner arrangement of the leaving groups to form the alkene. Hence, a ring flip occurs to give conformer (B). The energetics of the ring flip is offset by the energy released due to product formation; hence the reaction proceeds.