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L13a - Elimination Reactions OH H2SO Product 4distribution...

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1 1 Product distribution X Y ... X Z ... Y X ... Y Z ... Z X ... Z Y ... 2% 1% 0% 0% 95% 2% H 2 SO 4 140-170 o OH 1. X Y Z 2. X Z Y 3. Y X Z 4. Y Z X 5. Z X Y 6. Z Y X Major minor middle X Y Z 2 © Kay Sandberg β - Elimination Reactions: Section 5.13 Rearrangements in alcohol dehydration CH 3 CH 2 CH CH 2 12% C C H 3 C H CH 3 H 32% C C H 3 C H H CH 3 56% + + regioselective stereoselective CH 3 CH 2 CH 2 CH 2 OH H 2 SO 4 140-170 o 3 © Kay Sandberg H C H 3 C C H CH 3 Notice the spatial relationship of methyl groups H C H 3 C C CH 3 H Major minor G o cis - trans - reaction progression 4 ©Dr. Kay Sandberg Last lecture This lecture Alkene preparations Alkene reactions E1 mechanism dehydration of alcohols E2 mechanism dehydrohalogenation of alkyl halides 5 © Kay Sandberg Summary: Transformations involving alcohols Alkene formation: alcohol dehydration Alkyl halide formation C C H OH α β + H OH H + R —OH R —X + H —OH H —X In both (for 2 o & 3 o ROH), RDS is dissociation of alkyloxonium ion (unimolecular) forming H 2 O and C + . 6 © Kay Sandberg β - Elimination Reactions: Section 5.14 De hydro halogenation of alkyl halides C C H X α β + H X base C C H X α β + Na X Na OCH 2 CH 3 + H OCH 2 CH 3 O ppp product prediction purposes alkyl halide
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