CHEM 261 1st Edition Lecture 19Outline of Last Lecture:I. Markovnikov’s Rule/Hammond Postulate ReviewII. Addition with Substituted Cyclohexenes (Chiral/achiral)III. Carbocation RearrangementsOutline of Current Lecture:I. Halogenation of AlkenesII. Hydration of alkenesIII. Oxymercuration-Demercuration of AlkenesIV. Hydroboration-OxidationV. Adding H2 to Alknenes= Catalytic HydrogenationHalogenation of Alkenes:-Adding Cl2/Br2 (F2 is too reactive, I2 is too unreactive)Cl2 reaction proceeds as Cl- and Cl+ …not radicals-intermediate= chlorine attaches to BOTH carbons (not pictured). The intermediate isn’t a carbocation, but a “+” charge still exists on the chlorine bound to both carbons. -Cl- can’t attach to the side where the Cl+ is…must “attack” from the other sideIntermediate = chloronium/bromonium ionsCyclic Cl2 reaction:-Can also form with the opposite trans configuration (racemic mixture)-Cis product is not formed (**can’t “attack” from the same side!)Hydration of Alkenes:-Addition of H2O to alkenes alcohol. Need an acid!-Markovnikov type addition. OH- always ends up on the most substituted carbonOxymercuration-Demercuration of Alkenes:-Step 1: always Hg(OAc)2. Produces mercuronium ion.Hydroboration-Oxidation:Borane= BH3 = Lewis acid/ electron acceptorTHF= tetrahydrofuranAdd H2 to alkenes= Catalytic Hydrogenation-Adding H2 across the double bond. -H2 = gas, and need a metal (Pt, Pd, Ni, etc)Hand Written
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