Presentation on theme: "Outline for Today Review MO construction for Conjugated Systems Discuss Diels-Alder Reaction Chapter 14 – Aromaticity Tie in Aromaticity to Diels-Alder."— Presentation transcript:
Outline for Today Review MO construction for Conjugated Systems Discuss Diels-Alder Reaction Chapter 14 – Aromaticity Tie in Aromaticity to Diels-Alder Further Reading: Structure and Mechanism in Organic Chemistry By Felix A. Carrol Chapter 4.1-2 – MO theory/aromaticity Chapter 11.4 Cycloadditions Lectures available online at http://perceco2.chem.upenn.edu/~percec/classes.html http://perceco2.chem.upenn.edu/~percec/classes.html Until further notice.
Molecular Orbitals of Diels Alder Cycloaddition Normal Electron Demand/Inverse-Electron Demand/ Thermal Diels-AlderPhotochemical Diels-Alder
Normal versus Inverse Electron Demand NormalInverse
Woodward Hoffman Rules for Cycloadditons “A Reaction occurs when the bonding electrons of a product can be transferred, without a symmetry imposed barrier, to the bonding orbitals of the product.” Last Chapter of “The Conservation of Orbital Symmetry” – Exceptions? “There are none.”
Diels-Alder and Hückel Theory Transition state has 6=4n+2 where n=1 electrons, therefore is aromatic and low in energy, despite high entropic cost. Note: If Diels-Alder Substrate is Aromatic to begin with will often not participate.