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Lecture_22 - Lecture 22 Chapter 7 Delocalized ...

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Unformatted text preview: Lecture 22 Chapter 7: Delocalized Electrons Delocaliza8on Affects Product Outcome Reac8ons of Isolated Dienes •  Each react individually as we learned already •  If you only add 1 equiv, goes to more reac8ve double bond (most stable carboca8on) Reac8ons of Conjugated Dienes •  Direct addi8on and conjugate addi8on Reac8ons of Conjugate Addi8on •  1,2- addi8on products •  1,4- addi8on products Unsymmetrical Dienes •  2- methyl- 1,3- butadiene Thermo vs. Kine8c Control •  Kine8c product: most rapidly formed •  Thermo product: most stable •  At - 80°C you get 80% 20% •  At 45°C you get 15% 85% Proximity Effect •  Why is 1,2- product formed faster? –  Is it because of the transi8on state? Proximity Effect Diels- Alder Reac8on •  A type of [4+2] cycloaddi8on reac8on –  This is a concerted reac8on Molecular Orbital Descrip8on Interes8ng Products Diels- Alder •  Regioselec8vity can be predicted –  1- methoxy- 1,3- butadiene + acrolein –  Two possible regioisomers, which one is major? Diels- Alder •  s- cis and s- trans conforma8ons –  Locked s- trans do not react •  The Alder endo rule –  1,3- cyclopentadiene and methyl acrylate Stereochemistry of Diels- Alder •  Products with one stereocenter are racemic –  1,3- butadiene and methyl acrylate •  Diels- Alder reac8ons are stereospecific –  1,3- butadiene and (Z)- methyl- 2- butenoate Diels- Alder Products •  Suggest a diene and dienophile that could be used to make these products ...
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