E1: Regio- and Stereochemistry

E1: Regioselectivity and Stereochemistry

I. Regioselectivity: Zaitsev’s Rule

The E1 mechanism typically favors formation of the more substituted alkene, following Zaitsev’s Rule.

• Major product: The more substituted (and more stable) alkene.
• Reason: In the second step of the E1 mechanism, the base removes a proton from the β-carbon, leading to the most thermodynamically stable alkene.

Placeholder: [Chemical reaction: Example showing major (Zaitsev) and minor (Hofmann) alkene products]

II. Stereochemistry

E1 reactions are not stereospecific. Since the carbocation intermediate allows for rotation, both E and Z isomers can form.

• Thermodynamic control: The more stable isomer—typically the E isomer—is favored due to lower steric strain between substituents on opposite sides of the double bond.

Placeholder: [Chemical reaction: Example showing formation of both E and Z alkene isomers]