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Chapter30 - Pericyclic Reactions What are they 30 Orbitals...

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1 30. Orbitals and Organic Chemistry: Pericyclic Reactions Based on McMurry’s Organic Chemistry , 6 th edition ©2003 Ronald Kluger Department of Chemistry University of Toronto Based on McMurry, Organic Chemistry, Chapter 30, 6th edition, (c) 2003 2 Pericyclic Reactions – What are they? Involves several simultaneous bond-making breaking process with a cyclic transition state involving delocalized electrons The combination of steps is called a concerted process where intermediates are skipped Based on McMurry, Organic Chemistry, Chapter 30, 6th edition, (c) 2003 3 30.1 Molecular Orbitals of Conjugated π Systems A conjugated diene or polyene has alternating double and single bonds Bonding MOs are lower in energy than the isolated p atomic orbitals and have the fewest nodes Antibonding MOs are higher in energy See Figure 30.1 for a diagram Based on McMurry, Organic Chemistry, Chapter 30, 6th edition, (c) 2003 4 Molecular orbital principles Based on wave mechanics Whole molecule has orbitals but π orbitals are highest energy Transitions from HOMO to LUMO occur upon absorption of light of appropriate energy Energy levels of Molecular Orbitals are below and above atomic orbitals Conjugation gives extended orbitals
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