CONTENTS
CHAPTER 1 PERICYCLIC REACTIONS 1-126
• PERICYCLIC REACTIONS 1

FRONTIER ORBITAL APPROACH1 3
• CORRELATION DIAGRAMS 5

The p Molecular orbitals of cyclodhexadiene 10
• ORBITAL SYMMETRY IN CYCLOADDITION REACTIONS 11

Correlation Diagram 11
• HÜCKEL–MOBIUS(H–M) APPROACH FOR PERICYCLIC REACTIONS 14

AROMATIC TRANSITION STATE 14
• ELECTOCYCLIC REACTIONS 16

Examples of Thermal Electrocyclic Reactions 18
• Photochemical Electrocyclic Reactions 27
• Metal catalysed Eelctrocyclic Reactions 30

Electrocyclic reactions in ionic conjugated systems 32
• PROBLEMS RELATING ELECTROCYCLIC REACTIONS 35
• CYCLOADDITION REACTIONS 44
• Reactivity 53
• Regioselectivity 56
• Stereoselectivity and Endo effect 58
• Catalysis in Diels-Alder Reaction 63
• The Retro Diels-Alder Reaction 64
• Examples of Retro Diels-Alder Reactions 65

Mechanism : 66
• 1,3-DIPOLAR CYCLOADDTIONS 68

Examples of 1,3-Dipolar addition 69
Examples of 1,3-Dipolar Cycloadditions 72

• Retro 1,3-Dipolar Cycloadditions 77
• Photochemical Cycloaddtions 80

Multicomponent Cycloadditions 81
• Photochemical [2+2] Cycloadditions 81

• Other [2+2] Cycloadditions 84
• Retro [2+2] Additions 86

More examples of retro [2+2] cycloaddition reactions : 87
• Cheletropic Reactions 88

Addition of carbenes and nitrenes 90
Examples of Cheletropic Reactions and Extrusions 91

• [2+2+2] Cycloadditions and Eliminations 95
• [2 + 2 + 2 + 2] Cycloadditions (Four component addition) 97
• Theory of cycloaddition reactions with more than two components 97
• Group Transfer Reactions 98
• Correlation Diagram for the concerted Transfer of two Hydrogen

Atoms from Ethane to the Termini of Butadiene 99
• Prismane 100

Formation of π orbitals of benzene from σ orbitals of prismane : 101
• Dewar Benzene 102
• The Ene Reaction 105
• Retro ene Reactions 107
• The Cope Elimination and related reactions 110
• PROBLEMS RELATING CYCLOADDITION REACTIONS 112

Aromatic transition state approach : 118

CHAPTER 2 ORGANIC PHOTOCHEMISTRY 127-198
• Introduction 127

Thermal Energy 127
Activation Energy 128
Photochemical Energy 130

• PHOTOCHEMICAL EXCITATION 130
Light Absorption 130
Experimental Techiques 130
Electronic Transition 131

• JABLONSKI DIAGRAMS 132
Intersystem Crossing (ISC) 133
Energy Transfer 134

• Molecular Orbital View of Excitation 136
• The Geometry of Excited States 137
• PHOTOCHEMISTRY OF CARBONYL COMPOUNDS 138

Reactivity of Electronically Excited Ketones 138
Representation of Excited States of Ketones 138
Saturated Acyclic Carbonyl Caompounds 139

• PATERNO-BÜCHI REACTION 161
Limitations of Paterno-Büchi reaction : 164
Synthesis : 166

• PHOTOCHEMISTRY OF OLEFINS 172
• Geometrical Isomerism 173

Mechanism: 176
Aza Crown Ethers 184
Some more Problems and Applications of Photochemistry 186

• Photorearrangements 188
Charactersitics of Di-p Methane Rearrangement 188
Mechanism of the Reaction (Proposed by Zimmerman) : 192
Formation of other Products : 193

• The Transfer of Excitation Energy (Sensitisation and Quenching) 194
Collision Energy Transfer -Triplet sensitisation 195

CHAPTER 3 HÜCKEL MOLECULAR ORBITAL THEORY AND AROMATICITY 199-274
• 1. Molecular Orbital Theory (MOT) 199
• 2. HÜCKEL MOLECULAR ORBITAL THEORY (HMO THEORY) 201

IInteraction Matrix of Some Interacting p Orbitals 204
• CYCLIC SYSTEMS 210
• Resonance Energy or Delocalisation of Benzene 218
• Vertical resonance energy or delocalisation energy 219
• Molecular Orbital Theory and Aromaticity 219
• Concept of Aromaticity 220
• General Solution 221

Relative Arrangement of Energy Levels 222
Frost Diagram for Cyclopropenyl System 222
Frost diagram for Cyclobutadienyl System 224

• Alternant and Non-Alternant Hydrocarbons (AH and non -AH Hydrocarbons) 228
Examples of Aromatic Molecules 229
Energy level diagram of eight π electron system : 231
Preparation of (I) (1,6-methano [10] annulene) 233

• Aromaticity in Charged Rings 234
• Aromaticity in non-benzenoid compounds - Metallocenes 239
• HETEROCYCLIC COMPOUNDS 239

Aromaticity / Antiaromaticity in some heterocycles are shown as follows 240
• Fused Ring Systems 241
• Homoaromaticity 247
• Pseudoaromaticity 249
• More Examples of Aromatic and Antiaromaticity Compounds 249

CHAPTER 4 LINEAR FREE ENERGY RELATIONSHIP AND HAMMETT EQUATION 275-296
• THE SUBSTITUENT CONSTANT σ 275
• THE REACTION CONSTANT, ρ 277

The Significance of values 278
Typical Hammett plots 278

• The Hammett equation as a linear free energy relationship 278
• Reaction mechanisms and the Hammett equation 279

σ+ AND σ– CONSTANTS 284
• CURVED (OR NONLINEAR) HAMMETT PLOTS 285
• Non-linear Hammett Plots 286
• Non-linear Hammett Plots 289

Hydrolysis of the acid chloride of benzoic acids 294
• SOLVENT EFFECTS 295

INDEX 297-302