Factors affecting E1 and E2 reactions
- S-2-pharmaceutical-organic-chemistry
- Feb 24
- 1 min read
Updated: Mar 1
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Substrate Structure
E1: Prefers tertiary alkyl halides due to stable carbocations formed during the reaction.
E2: Works with a variety of substrates but requires the substrate to adopt an anti-periplanar geometry for effective proton abstraction.
Leaving Group
Affects both reactions. Better leaving groups (e.g., iodide, bromide) facilitate E1 and E2 mechanisms by stabilizing the negative charge upon departure.
Nucleophile/Base Strength
E1: Often involves a weak base or nucleophile, since the rate-determining step is carbocation formation.
E2: Requires a strong base to abstract a proton in the concerted step leading to the formation of a double bond.
Solvent
E1: Favored by polar protic solvents, which stabilize both the carbocation and leaving group, facilitating the reaction.
E2: Works best with polar aprotic solvents, which enhance the base's strength and aid the concerted elimination process.
Temperature
E2 reactions are typically favored at higher temperatures due to their higher activation energy, consistent with the endothermic nature of bond-breaking and simultaneous elimination.
These factors help determine whether an elimination reaction will proceed via the E1 or E2 mechanism and the efficiency of the process.
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