E2 Elimination (Dehydrohalogenation)

C₂H₅Br + KOH → C₂H₄ + KBr + H₂O

Overview

Strong base (KOH in ethanol) removes a beta-hydrogen and the halide leaves simultaneously in a concerted E2 elimination to form an alkene. The H and Br must be anti-periplanar (180 degrees) for the elimination to proceed. E2 competes with SN2, with bulky bases and secondary/tertiary substrates favoring elimination.

Participants

Role	Substance	Coefficient	State
Reactant	Potassium Hydroxide KOH	1	(aq)
Product	Ethylene C₂H₄	1	(g)
Product	Water H₂O	1	(l)

Everyday Example

E2 elimination is used to prepare alkenes from easily available alkyl halides and is key to understanding organic reaction selectivity.

Industrial Importance

Dehydrohalogenation is used in the manufacture of vinyl chloride (from ethylene dichloride) and in producing various alkene monomers.

Properties

Type: Organic
Reversible: No
Energy: Exothermic
ΔH: -50.0 kJ/mol

Related Reactions

Aldol Condensation of Acetaldehyde Amide Formation (Acetic Acid + Ammonia) Baeyer-Villiger Oxidation Beckmann Rearrangement (Cyclohexanone Oxime) Bromination of Ethylene Buchwald-Hartwig Amination Cannizzaro Reaction of Formaldehyde Catalytic Hydrogenation of Ethylene Claisen Condensation (Ethyl Acetate) Condensation Polymerization (Nylon 6,6)

Frequently Asked Questions

What is the equation for E2 Elimination (Dehydrohalogenation)?

The balanced equation is: C₂H₅Br + KOH → C₂H₄ + KBr + H₂O.

What type of reaction is E2 Elimination (Dehydrohalogenation)?

E2 Elimination (Dehydrohalogenation) is a organic reaction.

Is E2 Elimination (Dehydrohalogenation) exothermic or endothermic?

E2 Elimination (Dehydrohalogenation) is exothermic (releases energy). The enthalpy change (ΔH) is -50.0 kJ/mol.