A THEORETICAL STUDY OF THE REACTIVITY AND SYNTHESIS OF MOLECULES: APPLICATIONS AND EXTENSIONS OF THE THEORY OF ATOMS IN MOLECULES

Abstract

<p>This thesis applies and extends the theory of atoms in molecules to some general, important and chemically interesting subjects: a means of studying molecules of biochemical size using high-level quantum chemistry, the chemical reactivities of aromatic molecules as well as the nature of π-type hydrogen bonding.</p> <p>Quantum mechanical principles define an atom in a molecule and its properties as well as the chemical bonds which link the atoms to yield a molecular structure. The resulting theory is called the theory of atoms in molecules. The theory also predicts the chemical reactivity of a molecule through the properties of the Laplacian of its electronic charge distribution, the Laplacian of the charge density also provides the physical basis of the Lewis and VSEPR models. The theory is reviewed in Chapter 1.</p> <p>Molecules of biochemical interest always cause difficulties for computational chemists because of the size. Semiempirical methods have been used in the past. but must alternatively be replaced by ab initio theory. An attempt to use a nonempirical method with reliable trial functions to solve such problems, as made possible through the application of the tools provided in the theory of atoms in molecules, is presented in Chapter 2, and gives ml encouraging result.</p> <p>The study of the chemical reactivities of aromatic I10lecules is of general interest to chemists. An enormous amount of research has been done in this area. A new way of using the theory to study the reactivities and energetics of monosubstituted benzenes and their para and meta protonated intermediates is presented in Chapters 3 and 4. The directing ability of a substituent and its ability to activate or deactivate the phenyl group in electrophilic substitution reaction are related to atomic, bond and molecular properties of the aromatic molecules.</p> <p>The nature of π-type hydrogen bonding is discussed in Chapter 5. The molecular structures of three C₈H₈HF complexes are determined for the first time.</p>