On June 2nd, 2008, Dr. Simon C.A.H. Pierrefixe successfully defended his Ph.D. thesis entitled
“Hypervalence and Aromaticity”.
Dr. Simon Pierrefixe was supervised by copromotor Dr. Matthias Bickelhaupt (promotor Prof. Dr. Evert Jan Baerends). A PDF file of this thesis is available from the Ph.D. Theses section. Contact SCM to obtain a free paper copy in book form (limited availability).
The main purpose of his thesis is to gain more insight into the origin of the choice of nature between delocalized structures with equal bonds and localized structures with short and long bonds for some well-known (non)hypervalent and (anti)aromatic systems. In fact, the very concepts of hypervalence and aromaticity themselves are the subject of analysis. The required insight is obtained in this thesis from electronic structure theory by developing qualitative physical models based on Molecular Orbital (MO) theory as contained in the Kohn-Sham approach to density functional theory (DFT). The ADF program was used in accurate DFT calculations in order to understand which feature in the bonding mechanism is essential for determining whether an atom can form a hypervalent structure (or not) or whether a π-conjugated ring adopts an aromatic geometry with delocalized double bonds (or not).