What product(s) are expected in the ethoxide-promoted ß-elimination reaction of 1-chloro-1-methylcyclohexane? Omit ions, salts, and ethanol from your response. Draw the product(s).
The correct answer and explanation is :
Answer:
The expected product of the ethoxide-promoted β-elimination reaction of 1-chloro-1-methylcyclohexane is 1-methylcyclohexene.
Explanation:
The reaction mechanism follows the E2 (bimolecular elimination) mechanism, which occurs under strong base conditions like ethoxide (EtO⁻). Here’s how the reaction proceeds:
- Formation of the Transition State:
- The strong base (EtO⁻) abstracts a β-hydrogen (H) from the carbon adjacent to the carbon bearing the leaving group (Cl).
- This removal of the proton must occur in an anti-periplanar (coplanar but opposite-facing) geometry to the leaving group for the best orbital alignment, which is characteristic of an E2 mechanism.
- Elimination of the Leaving Group:
- As the β-hydrogen is removed, the electrons from the C-H bond shift to form a π bond between the α- and β-carbons.
- Simultaneously, the chlorine (Cl⁻) leaves, forming the alkene.
- Formation of the Alkene Product:
- Since 1-chloro-1-methylcyclohexane has only one available β-hydrogen (on the β-carbon adjacent to the chlorine), only one possible alkene product can form: 1-methylcyclohexene.
- The formation of a double bond follows Zaitsev’s rule, which states that the most substituted and stable alkene is preferentially formed.
Why Only 1-Methylcyclohexene?
- The β-hydrogen on carbon-2 is eliminated, leading to the formation of 1-methylcyclohexene.
- No regioisomeric products are formed because the only β-hydrogen available leads directly to the formation of this particular alkene.
Summary:
- The reaction follows an E2 mechanism because of the strong base (ethoxide).
- The product is 1-methylcyclohexene as dictated by Zaitsev’s rule.
- The elimination requires an anti-periplanar conformation, ensuring that elimination proceeds in a single step without intermediates.
Thus, 1-methylcyclohexene is the sole product of this reaction.