dehydrohalogenation

chemical reaction

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June 25, 2026

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Dehydrohalogenation is a type of elimination reaction in organic chemistry where a hydrogen atom and a halogen atom are removed from a molecule. This process typically transforms saturated compounds, which contain only single carbon-carbon bonds, into unsaturated compounds with double or triple carbon-carbon bonds.1

This reaction is a key method for preparing alkenes, which are unsaturated hydrocarbons. For instance, alkyl halides, a class of organohalogen compounds, readily undergo dehydrohalogenation when treated with a strong base. This reaction competes with nucleophilic substitution, especially with secondary and tertiary alkyl halides. The mechanism is often classified as E2, indicating an elimination reaction that is bimolecular.23

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elimination reaction
…for example, is known as dehydrohalogenation; when both leaving atoms are halogens, the reaction is known as dehalogenation. Similarly, the elimination of a water molecule, usually from an alcohol, is known as dehydration; when both leaving atoms are hydrogen atoms, the reaction is known as dehydrogenation. Elimination reactions are also…
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…for example, is known as dehydrohalogenation; when both leaving atoms are halogens, the reaction is known as dehalogenation. Similarly, the elimination of a water molecule, usually from an alcohol, is known as dehydration; when both leaving atoms are hydrogen atoms, the reaction is known as dehydrogenation. Elimination reactions are also…
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organohalogen compound
Dehydrohalogenation of a dihalide
Treatment of a geminal dihalide (both halogens on the same carbon) or a vicinal dihalide (halogens on adjacent carbons) with a base such as sodium ethoxide (NaOCH₂CH₃) yields a vinylic halide.
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Treatment of a geminal dihalide (both halogens on the same carbon) or a vicinal dihalide (halogens on adjacent carbons) with a base such as sodium ethoxide (NaOCH₂CH₃) yields a vinylic halide.
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