Cyclopropyl Homoconjugation, Homoaromaticity and Homoantiaromaticity—Theoretical Aspects and Analysis

This chapter contains sections titled: Introduction Models in Chemistry Organization of the Chapter Definition of Homoconjugation and Homoaromaticity—Basic Considerations From Conjugation to Cyclopropyl Homoconjugation Conjugation Homoconjugation From a Topological to a Chemical Definition of Homoconjugation The Concept of Electron or Bond Delocalization A Definition of Homoconjugation Based on the Concept of Bond (Electron) Delocalization The Choice of Appropriate Reference Compounds Homoaromaticity and Homoantiaromaticity Homoconjugation and the Topology of the Potential Energy Surface: From Homoaromaticity to Frozen Transition States Theoretical Aspects of Defining, Detecting and Describing Homoconjugation and Homoaromaticity Winstein's Definition of Homoaromaticity Description of Homoconjugative Interactions in Terms of Orbital Overlap The Homotropenylium Cation as a Test Case The PMO Description of Homoaromaticity Description of a Homoconjugative Bond by Bond Orders and Other Interaction Indices The Electron Density Based Definition of a Homoconjugative Bond Description of Homoaromaticity in Terms of the Properties of the Electron Density Distribution Energy‐based Definitions of Homoaromaticity Direct Calculation of Homoaromatic Stabilization Energies Homoaromatic Stabilization Energies from Calculations with a Model Hamiltonian Evaluation of Homoaromatic Stabilization Energies by Using Isodesmic Reactions Evaluation of Homoaromatic Stabilization Energies by Using Homodesmotic Reactions Homoconjugative Resonance Energies from Force Field Calculations Ab initio Examinations of Homoconjugation Basic Requirements Investigation of the Homotropenylium Cation Ab Initio Calculations of Geometry and Energy Determination of the Equilibrium Geometry by the ab initio/Chemical Shift/NMR Method Toward a General Definition of Homoaromaticity Bond Homo(anti)aromaticity Caused by Cyclopropyl Homoconjugation No‐bond Homoaromaticity General Remarks Conclusions and Outlook Acknowledgements References Introduction Models in Chemistry Organization of the Chapter Models in Chemistry Organization of the Chapter Definition of Homoconjugation and Homoaromaticity—Basic Considerations From Conjugation to Cyclopropyl Homoconjugation Conjugation Homoconjugation From a Topological to a Chemical Definition of Homoconjugation The Concept of Electron or Bond Delocalization A Definition of Homoconjugation Based on the Concept of Bond (Electron) Delocalization The Choice of Appropriate Reference Compounds Homoaromaticity and Homoantiaromaticity Homoconjugation and the Topology of the Potential Energy Surface: From Homoaromaticity to Frozen Transition States From Conjugation to Cyclopropyl Homoconjugation Conjugation Homoconjugation Conjugation Homoconjugation From a Topological to a Chemical Definition of Homoconjugation The Concept of Electron or Bond Delocalization A Definition of Homoconjugation Based on the Concept of Bond (Electron) Delocalization The Choice of Appropriate Reference Compounds The Concept of Electron or Bond Delocalization A Definition of Homoconjugation Based on the Concept of Bond (Electron) Delocalization The Choice of Appropriate Reference Compounds Homoaromaticity and Homoantiaromaticity Homoconjugation and the Topology of the Potential Energy Surface: From Homoaromaticity to Frozen Transition States Theoretical Aspects of Defining, Detecting and Describing Homoconjugation and Homoaromaticity Winstein's Definition of Homoaromaticity Description of Homoconjugative Interactions in Terms of Orbital Overlap The Homotropenylium Cation as a Test Case The PMO Description of Homoaromaticity Description of a Homoconjugative Bond by Bond Orders and Other Interaction Indices The Electron Density Based Definition of a Homoconjugative Bond Description of Homoaromaticity in Terms of the Properties of the Electron Density Distribution Energy‐based Definitions of Homoaromaticity Direct Calculation of Homoaromatic Stabilization Energies Homoaromatic Stabilization Energies from Calculations with a Model Hamiltonian Evaluation of Homoaromatic Stabilization Energies by Using Isodesmic Reactions Evaluation of Homoaromatic Stabilization Energies by Using Homodesmotic Reactions Homoconjugative Resonance Energies from Force Field Calculations Winstein's Definition of Homoaromaticity Description of Homoconjugative Interactions in Terms of Orbital Overlap The Homotropenylium Cation as a Test Case The Homotropenylium Cation as a Test Case The PMO Description of Homoaromaticity Description of a Homoconjugative Bond by Bond Orders and Other Interaction Indices The Electron Density Based Definition of a Homoconjugative Bond Description of Homoaromaticity in Terms of the Properties of the Electron Density Distribution Energy‐based Definitions of Homoaromaticity Direct Calculation of Homoaromatic Stabilization Energies Homoaromatic Stabilization Energies from Calculations with a Model Hamiltonian Evaluation of Homoaromatic Stabilization Energies by Using Isodesmic Reactions Evaluation of Homoaromatic Stabilization Energies by Using Homodesmotic Reactions Homoconjugative Resonance Energies from Force Field Calculations Direct Calculation of Homoaromatic Stabilization Energies Homoaromatic Stabilization Energies from Calculations with a Model Hamiltonian Evaluation of Homoaromatic Stabilization Energies by Using Isodesmic Reactions Evaluation of Homoaromatic Stabilization Energies by Using Homodesmotic Reactions Homoconjugative Resonance Energies from Force Field Calculations Ab initio Examinations of Homoconjugation Basic Requirements Investigation of the Homotropenylium Cation Ab Initio Calculations of Geometry and Energy Determination of the Equilibrium Geometry by the ab initio/Chemical Shift/NMR Method Toward a General Definition of Homoaromaticity Bond Homo(anti)aromaticity Caused by Cyclopropyl Homoconjugation No‐bond Homoaromaticity General Remarks Basic Requirements Investigation of the Homotropenylium Cation Ab Initio Calculations of Geometry and Energy Determination of the Equilibrium Geometry by the ab initio/Chemical Shift/NMR Method Ab Initio Calculations of Geometry and Energy Determination of the Equilibrium Geometry by the ab initio/Chemical Shift/NMR Method Toward a General Definition of Homoaromaticity Bond Homo(anti)aromaticity Caused by Cyclopropyl Homoconjugation No‐bond Homoaromaticity General Remarks Bond Homo(anti)aromaticity Caused by Cyclopropyl Homoconjugation No‐bond Homoaromaticity General Remarks Conclusions and Outlook Acknowledgements References