6.8 The HOMO and LUMO Concept of Electronic Transitions The Selection Rules for Electronic Transitions Physical Properties of

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1 Contents Part I Pericyclic Reactions 1 General Aspects of Pericyclic Reactions Introduction Molecular Orbitals and Their Symmetry Properties Classification of Pericyclic Reactions Concertedness of Pericyclic Reactions Orbital Symmetry Property of Pericyclic Reactions Further Reading References Electrocyclic Reactions Introduction Orbital Symmetry Basis for Stereospecificity The Orbital Correlation Diagrams of Reactants and Products Applications of Neutral Conjugated Systems in Electrocyclic Reactions Applications of Ionic Conjugated Systems in Electrocyclic Reactions Problems Further Reading References Cycloaddition Reactions Introduction [2+2]-Cycloaddition Reactions Overview of Thermal and Photochemical [2+2]-Cycloaddition Reactions Applications of [2+2]-Cycloaddition Reactions [4+2]-Cycloaddition Reactions The Diels Alder Reactions ix

2 x Contents 3.4 Cycloaddition Reactions of More Than Six Electrons Systems: [4+4]-, [6+6]-, [6+4]-, [8+2]-, [12+2]-, and [14+2]-Cycloadditions Cheletropic Reactions Overview of Cheletropic Reactions Applications of Cheletropic Reactions Problems Further Reading References Sigmatropic Rearrangements Introduction Orbital Symmetry Basis for Allowed and Forbidden Sigmatropic Rearrangements and Their Stereochemistry Orbital Symmetry Analysis of [1,3]-, [1,5]-, and [1,7]-Sigmatropic Shifts of Hydrogen and Alkyl Groups Orbital Symmetry Analysis of [3,3]- and [2,3]-Sigmatropic Rearrangements [1,3]-, [1,5]-, and [1,7]-Sigmatropic Hydrogen and Alkyl Shifts and Their Applications [1,3]-Sigmatropic Hydrogen and Alkyl Shifts [1,5]-Sigmatropic Hydrogen and Alkyl Shifts [1,7]-Sigmatropic Hydrogen and Alkyl Shifts [3,3]-Sigmatropic Rearrangements The Cope Rearrangements The Oxy-Cope and the Anionic Oxy-Cope Rearrangements The Amino- and Aza-Cope Rearrangements The Claisen Rearrangements and Their Modified Versions: The Carroll, Eschenmoser, Ireland, Johnson, Gosteli, Bellus, and Enzymatic Claisen Rearrangements The Thio- and Aza-Claisen Rearrangements [2,3]-Sigmatropic Rearrangements Overview of Different Types of [2,3]-Sigmatropic Rearrangements [2,3]-Sigmatropic Rearrangements of Allyl Ammonium Ylides [2,3]-Sigmatropic Rearrangements of Benzyl Ammonium Ylides: The Sommelet Hauser Rearrangement [2,3]-Sigmatropic Rearrangement of Allyl Sulfonium Ylides

3 Contents xi [2,3]-Sigmatropic Rearrangements of Allyl Sulfoxides: The Mislow Evans Rearrangements [2,3]-Sigmatropic Rearrangements of Allyl Selenoxides [2,3]-Sigmatropic Rearrangements of Anions of Allyl Ethers: The Wittig and Aza-Wittig Rearrangements [2,3]-Sigmatropic Rearrangements of Allyl Amine Oxides: The Meisenheimer Rearrangement [3,5]-Sigmatropic Rearrangement [4,5]-Sigmatropic Rearrangement [5,5]-Sigmatropic Rearrangement [9,9]-Sigmatropic Rearrangement Problems Further Reading References Group Transfer Reactions Introduction The Ene Reactions Overview of the Ene Reactions Stereochemistry and Regioselectivity Applications of Intermolecular-, Intramolecular-, and Enantioselective-Ene Reactions The Metallo-Ene Reactions The Retro-Ene Reactions Diimide and Related Reductions Thermal Elimination Reactions of Xanthates, N-Oxides, Sulfoxides, and Selenoxides Problems Further Reading References Part II Photochemical Reactions 6 Principles of Photochemical Reactions Introduction Light Sources Used in Photochemical Reactions Laws of Photochemistry The Beer Lambert s Law of Light Absorption Physical Basis of Light Absorption by Molecules: The Franck Condon Principle Electronic Transitions and Their Nomenclature Spin Multiplicity of Electronic States

4 xii Contents 6.8 The HOMO and LUMO Concept of Electronic Transitions The Selection Rules for Electronic Transitions Physical Properties of Excited States: Jablonski Diagram Lifetimes of Electronic Excited States Efficiency of Photochemical Processes: Quantum Yield of Photochemical Reaction Intramolecular Process of Excited States: Fluorescence and Phosphorescence Fluorescence and Its Measurement Kasha s Rule for Fluorescence Vavilov s Rule for Fluorescence Phosphorescence and Its Measurement Intermolecular Physical Processes of Excited States: Photosensitization Processes Photosensitization/Quenching and Excimer/Exciplex Formation The Stern Volmer Equation for Determination of Quenching Rate Deviation from Stern Volmer Kinetics The Excimers and Exciplexes Long-Range Energy Transfer Process: The FRET Process Short-Range Energy Transfer Process: The Dexter Theory of Energy Transfer Photodynamic Tumor Therapy Using Singlet Oxygen Photo-induced Electron Transfer (PET) Process The Marcus Theory of Electron Transfer Photochemical Reactions and Their Kinetics Determination of the Excited State Configuration Determination of the Yield of Products Determination of the Lifetime of Intermediates Low-Temperature Matrix Studies Further Reading References Photochemistry of Alkenes, Dienes, and Polyenes Introduction Cis Trans-Isomerizations Cis Trans-Isomerizations of Alkenes Cis Trans-Isomerization of Dienes Photochemical Electrocyclic and Addition Reactions

5 Contents xiii 7.4 Photochemical [2+2]-Cycloaddition and Dimerization Reactions Photochemical Rearrangements The di-p-methane Rearrangements The aza-di-p-methane Rearrangements The tri-p-methane Rearrangements Problems Further Reading References Photochemistry of Carbonyl Compounds Introduction Hydrogen Abstraction and Fragmentation Reactions Cycloaddition and Rearrangement Reactions of Unsaturated Carbonyl Compounds Isomerization of Unsaturated Carbonyl Compounds Cycloaddition Reactions of Carbonyl Compounds with Alkenes Limitations Problems Further Reading References Photochemistry of Aromatic Compounds Introduction Photoisomerization Reactions of Aromatic Compounds Photocycloaddition Reactions of Aromatic Compounds with Unsaturated Compounds Photo-Diels Alder Cycloaddition Reactions of Aromatic Compounds Photo-Induced Hydrogen Abstraction and Addition Reactions of Aromatic Compounds Photocyclization Reactions of Aromatic Compounds Photorearrangement Reactions of Aromatic Compounds Photooxidation Reactions of Aromatic Compounds Photodimerization Reactions of Aromatic Compounds Photosubstitution Reactions of Aromatic Compounds Problems Further Reading References Photofragmentation Reactions Introduction The Barton Reaction The Hypohalite Reactions The Hofmann-Löffler-Freytag Reaction

6 xiv Contents 10.5 Problems Further Reading References Photochemistry in Nature and Applied Photochemistry Introduction Depletion of Stratospheric Ozone Layer from Photochemical Degradation Photochemical Smog in Polluted Zones of Troposphere Photochemistry of Vision: Geometrical Isomerisation of Retinal Phototherapy of Neonatal Jaundice Photosynthesis of Plants and Bacteria Artificial Photosynthesis Photo-Induced DNA-Damage and Its Repair Conservation of Solar Energy as Electrical Energy: Photovoltaic Solar Cells Photo-Induced Supramolecular Devices Further Reading References Appendix Index

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