Final answer:
An E2 reaction requires restricted rotation to maintain proper orientation, nonidentical groups on each doubly bonded carbon, and decreased steric crowding around the alpha carbon in the chair conformation.
Step-by-step explanation:
For an E2 reaction to occur in a chair conformation, certain requirements must be met to facilitate the reaction:
- Rotation must be restricted in the molecule to ensure the correct alignment of atoms for the elimination to take place.
- The molecule must have two nonidentical groups on each doubly bonded carbon atom, which is essential for the formation of the pi bond in the alkene product.
- A proper orientation must be achieved during the collision of the reacting species, which means that a base must approach the β-hydrogen anti-periplanar to the leaving group in order for the elimination to be effective.
- Decreasing steric crowding around the alpha carbon (aC) increases the likelihood of an E2 mechanism, particularly with tertiary substrates.
The chair conformation is preferred over other conformations, such as the twisted or boat forms, as it is of lower energy and provides the necessary anti-periplanar orientation for a successful E2 reaction.