Page 26

Question 1

Regioselectivity of E2 Reactions

Answer 1

Definition:
• A reaction is regioselective when it produces predominantly or exclusively one constitutional isomer out of multiple possible isomers.

Question 2

E2 Reactions Are Regioselective:

Answer 2

• They favor the formation of the more substituted alkene, which is typically the more stable product.

Question 3

Example Reaction:

Answer 3

• Starting compound: 2-bromo-2-methylbutane.
• Two possible elimination pathways:
• β₁ C-H bond cleavage leads to a disubstituted alkene (minor product, less stable).
• β₂ C-H bond cleavage leads to a trisubstituted alkene (major product, more stable).

Question 4

Stability of Transition States:

Answer 4

• Transition states leading to more substituted alkenes (trisubstituted) are more stable due to better hyperconjugation and alkyl substituent effects.
• The less substituted alkene (disubstituted) forms through a less stable transition state, making it the minor product.