Chem 261 1st Edition Lecture 20Outline of Last Lecture:I. Halogenation of AlkenesII. Hydration of alkenesIII. Oxymercuration-Demercuration of AlkenesIV. Hydroboration-OxidationV. Adding H2 to Alknenes= Catalytic HydrogenationOutline of Current lecture:I. Making Alkenes: Addition/EliminationII. HalogenationIII. Generating halohydrinsIV. Acid-Catalyzed HydrationV. Oxymercuration/DemercurationVI. Hydroboration/OxidationMaking Alkenes: Addition/Elimination:-The above reaction is an example of an addition reaction, in which the alkene and another molecule, X-Y, are summed together to produce a new compound. The reverse of this reaction, in which X-Y and an alkene are yielded, is an elimination reaction. Elimination Reactions:1. Dehydrohalogenation-lose water from an alkyl halide-also called 1,2 (or β) elimination2. Dehydration*H3PO4 is also a good in these types of reactionsRxn w/o solvent = heat!Halogenation:Ex. With Br2, there is a partial positive and a partial negative charge. No reaction occurs with thepositively charged Br. Attach X- on the opposite side of the chloroniumGenerating Halohydrins:**concerted mechanism: steps happen at the same timeNBS mechanism:-Can generate halohydrins with NBSAcid-Catalyzed Hydration:-Utilizes H2SO4 or H3PO4 typically, Markovnikov product is the most substituted. -There are many steps to these reactions to produce the final product (**note, want to produce ONE final product, not a mixture!)Oxymercuration/Demercuration:-Also a concerted reaction mechanism-in the above reaction, NaBH4 is the reducing agentHydroboration/Oxidation:-also a concerted reaction mechanismHAND WRITTEN NOTES NEXT
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