Orbital Models and the Electron Distribution: Applications and Extensions of the Theory of Atoms
This thesis explores the relationship between the recently developed theory of atoms in molecules and the simple orbital models of electronic structure which form the basis of current chemical thinking. In so doing it provides a new viewpoint form which to study many essential chemical concepts: concepts originating from qualitative orbital models.
The formal aspects of the theory of atoms in molecules are reviewed. Developed in the laboratory of Professor Bader, this theory provides a quantum mechanical definition of an atom in a molecule and its properties. It also exploits the observed topology of the electron density to the define molecular structure and its change.
The relationship between qualitative orbital models and atomic and bond critical properties is analysed, first qualitatively and then quantitatively. The analysis starts with a study of atomic properties and the properties of bond critical points in diatomic hydrides and some simple organic molecules. A theoretical framework is then developed within which chemical effects on molecular electron distributions can be studies and interpreted.
The framework is used in a study of substituent effects on the ethyl, vinyl and carbonyl groups, and then applied to two other problems -- the interpretation of protonation energies of carbonyl compounds and an investigation of the concept of homoaromaticity.