07. Alkenes - E reaction 2010

07. Alkenes - E reaction 2010 - Alkenes and Alkynes...

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1 CHEM 212 Nicolas Moitessier Alkenes and Alkynes Elimination Reaction
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2 CHEM 212 Nicolas Moitessier ± Introduction / Preparation Ch. 7.1-7.5 ± Dehydrohalogenation: An E2 reaction Ch.7.6 ± Outcome of the Elimination reactions Ch.7.6 ± Dehydration reaction, elimination and rearrangement Ch.7.7-7.8 ± Reduction on Alkenes Ch.7.3-7.15
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3 CHEM 212 Nicolas Moitessier Introduction ± Relative Stabilities of Alkenes z Generally cis alkenes are less stable than trans alkenes because of steric hinderance z Cis alkenes are more reactive than trans alkenes (hydrogenation reaction)
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4 CHEM 212 Nicolas Moitessier Introduction ± Relative Stabilities of Alkenes z The more highly substituted double bond, the greater the alkene’s stability tetrasubstituted > trisubstituted > disubsituted > monosubstituted z Within the disubstituted series: 1,1 disubstituted > trans > cis >
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5 CHEM 212 Nicolas Moitessier Preparation ± Dehydrohalogenation ± Addition X H B X H B X H R NaNH 2 R
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6 CHEM 212 Nicolas Moitessier X H B HB X Elimination Reaction ± Dehydrohalogenation z Used for the synthesis of alkenes H B
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7 CHEM 212 Nicolas Moitessier Alkoxides ± The alkoxide bases are made from the corresponding alcohols Na o CH CH 2 OH CH 3 CH 2 O Na NaH CH CH 2 OH CH 3 2 O Na
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8 CHEM 212 Nicolas Moitessier ± Introduction / Preparation Ch. 7.1-7.5 ± Dehydrohalogenation: An E2 reaction Ch.7.6 ± Outcome of the Elimination reactions Ch.7.6 ± Dehydration reaction, elimination and rearrangement Ch.7.7-7.8 ± Reduction on Alkenes Ch.7.3-7.15
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9 CHEM 212 Nicolas Moitessier Dehydrohalogenation: An E2 Reaction ± Base removes a proton on the β -carbon ± TS: developing double bond, leaving X z concerted removal of the proton, formation of the double bond, and departure of the leaving group z Both alkyl halide and base concentrations affect rate and therefore the reaction is 2nd order X H B HB X HB X H B X H B B H
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10 CHEM 212 Nicolas Moitessier The E2 Reaction ± Concerted removal of the proton, formation of the double bond, and departure of the leaving group ± Both alkyl halide and base concentrations affect rate z the reaction is 2nd order Rate = k [CH 3 CHBrCH 3 ] [CH 3 CH 2 O - ] Br H O X H B CH 3 C 2 H 5
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11 CHEM 212 Nicolas Moitessier Elimination vs. Substitution ± Elimination competes with substitution reaction z Strong bases such as alkoxides favor elimination H 3 C CH 3 X CH 3 MeO Na C H H H MeOH NaBr H H 3 C C CH 3 H H
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12 CHEM 212 Nicolas Moitessier The E1 Reaction X H H Step 1 + B + H Step 2
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13 CHEM 212 Nicolas Moitessier
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This note was uploaded on 11/15/2010 for the course CHEM 212 taught by Professor Harpp during the Spring '08 term at McGill.

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07. Alkenes - E reaction 2010 - Alkenes and Alkynes...

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