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Chem357__Polyene_Chem__FINAL_Student_

Chem357__Polyene_Chem__FINAL_Student_ - Reactions of Dienes...

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1 Reactions of Reactions of Dienes Dienes Paula Y. Paula Y. Bruice Bruice , , Chapter 7 Chapter 7 2 Simple versus Simple versus Non-conjugated Non-conjugated Dienes Dienes H Br Br (+ enantiomer) H Br (excess) Br Br H Simple Alkene Non-conjugated Diene NOTE: Each double bond reacts as if it was a simple alkene.
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3 H Br (excess) Br Br H Br Br H Br H Br Br Br H Br H Br (2 R ,4 S )-2,4-dibromo-4-methylhexane (2 S ,4 R )-2,4-dibromo-4-methylhexane (2 R ,4 R )-2,4-dibromo-4-methylhexane (2 S ,4 S )-2,4-dibromo-4-methylhexane enantiomers diasteriomers enantiomers diasteriomers Non-conjugated Diene NOTE: Each double bond reacts as if it was a simple alkene. Non-conjugated Non-conjugated Diene Diene 4 H Br (1 equiv.) Non-conjugated Diene If we had ONLY one equivalent of H-X, can we predict a MAJOR product? ? Non-conjugated Non-conjugated Diene Diene
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5 Non-conjugated Non-conjugated Diene Diene Free Energy Reaction Coordinate T.S. 2 T.S. 2 T.S. 1 T.S. 1 H Br S.M. 3 o carbo- cation 2 o carbo- cation H a m m o n d P o s t u l a t e .... the transition state is more similar in structure to the species to which it is more similar to in energy. (pg 164) ! G ! G Products 6 Conjugated Conjugated Dienes Dienes sp 3 Conjugated Non-conjugated H Br (1 equiv.) Non-conjugated Diene CH 2 CH CH CH 2 buta-1,3-diene CH 2 CH CH CH 2 3-bromobut-1-ene CH 2 CH CH CH 2 1-bromobut-2-ene + Br H Br H (1,2-addition product) (1,4-addition product) 1 2 3 4 1 2 3 4 1 2 3 4
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7 Conjugated Conjugated Dienes Dienes H Br (1 equiv.) Br Br 1,4-product 1,2-product Br Br 8 H Br (1 equiv.) Br Br Predicting MAJOR Products...
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