Hofmann elimination

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Not to be confused with Hofmann rearrangement.
Hofmann elimination
Named after August Wilhelm von Hofmann
Reaction type Elimination reaction
Identifiers
Organic Chemistry Portal hofmann-elimination
RSC ontology ID RXNO:0000166

Hofmann elimination is an

Zaitsev's rule predicts the formation of the most stable alkene. It is named after its discoverer, August Wilhelm von Hofmann.[1][2]

The reaction starts with the formation of a

steric bulk of the leaving group
causing the hydroxide to abstract the more easily accessible hydrogen.

An 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 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.[3]

An example of a Hofmann elimination (not involving a contrast between a Zaitsev product and a Hofmann product) is the synthesis of

trans-cyclooctene
article for better images):

Synthesis of trans-cyclooctene

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 to the quaternary ammonium salt which when heated degrades to methyl iodide and the secondary amine.[5]

See also

References

  1. S2CID 108453887
    .
  2. doi:10.1002/jlac.18510780302
    .
  3. ^ Wade, p. 903.
  4. ^ Arthur C. Cope; Robert D. Bach (1973). "trans-Cyclooctene". Organic Syntheses; Collected Volumes, vol. 5, p. 315.
  5. doi:10.1002/cber.18940270163
    .

External links
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