Hofmann elimination is an elimination reaction of an amine to form alkenes. The least stable alkene (the one with the least number of substituents on the carbons of the double bond), called the Hofmann product, is formed. This tendency, known as the Hofmann alkene synthesis rule, is in contrast to usual elimination reactions, where Zaitsev's rule predicts the formation of the most stable alkene. It is named after its discoverer, August Wilhelm von Hofmann. The reaction starts with the formation of a quaternary ammonium iodide salt by treatment of the amine with excess

methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...

(exhaustive methylation), followed by treatment with silver oxide and water to form a quaternary ammonium hydroxide. When this salt is decomposed by heat, the Hofmann product is preferentially formed due to the

steric bulk Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...

of the leaving group causing the hydroxide to abstract the more easily accessible hydrogen. : Example of the Hofmann Elimination Reaction

In the Hofmann elimination, the least substituted alkene is typically favored due to intramolecular steric interactions. The quaternary ammonium group is large, and interactions with alkyl groups on the rest of the molecule are undesirable. As a result, the conformation necessary for the formation of the Zaitsev product is less energetically favorable than the conformation required for the formation of the Hofmann product. As a result, the Hofmann product is formed preferentially. The

Cope elimination The Cope reaction or Cope elimination, developed by Arthur C. Cope, is an elimination reaction of the N-oxide to form an alkene and a hydroxylamine. Mechanism and applications The reaction mechanism involves an intramolecular 5-membered cyclic tr ...

is very similar to the Hofmann elimination in principle, but occurs under milder conditions. It also favors the formation of the Hofmann product, and for the same reasons. An example of a Hofmann elimination (not involving a contrast between a Zaitsev product and a Hofmann product) is the synthesis of trans-cyclooctene. The ''trans'' isomer is selectively trapped as a complex with silver nitrate (in this diagram the ''trans'' form looks like a ''cis'' form, but see the trans-cyclooctene article for better images): : In a related chemical test, known as the Herzig–Meyer alkimide group determination, a tertiary amine with at least one methyl group and lacking a beta-proton is allowed to react with

hydrogen iodide Hydrogen iodide () is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under sta ...

to the quaternary ammonium salt which when heated degrades to methyl iodide and the secondary amine.

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An animation of the mechanism of the Hofmann elimination
{{DEFAULTSORT:Hofmann Elimination Elimination reactions Olefination reactions Name reactions

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