Ch 6: Alkene + H3O+ - Chemistry - University Of Calgary

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Return to Contents Chapter 6: Reactions of Alkenes: Addition Reactions Ch 6 contents
Hydration of Alkenes hydration of alkenes Reaction type: Electrophilic Addition

Summary

  • When treated with aq. acid, most commonly H2SO4, alkenes form alcohols.
  • Electrophile : H+
  • Regioselectivity predicted by Markovnikov's rule
  • Reaction proceeds via protonation to give the more stable carbocation intermediate.
  • Not stereoselective since reactions proceeds via a planar carbocation.
Related reactions
  • Reaction of alkenes with hydrogen halides, HX
  • Hydroboration / oxidation of alkenes
  • Hydration of alkynes
MECHANISM FOR REACTION OF ALKENES WITH H3O+
Step 1: An acid / base reaction. Protonation of the alkene to generate the more stable carbocation. The pi electrons act as a Lewis base. addition of H2O to C=C
Step 2: Attack of the nucleophilic water molecule on the electrophilic carbocation creates an oxonium ion.
Step 3: An acid / base reaction. Deprotonation by a base generates the alcohol and regenerates the acid catalyst.
In this scheme, examples of what the B: could be inlcude the conjugate base of the acid catalyst (e.g. HSO4-), the C=C in the starting material or a molecule of H2O.
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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary

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