Energy Changes in Relation to the Electronic Charge Distribution: I. Hydrogen Bond Formation. II. Rotation and Inversion Barriers. III. Hydrolysis Reactions of "High-Energy" Phosphorus Compounds

Abstract

<p>This thesis is an investigation into the relationship between changes in the distribution of electronic charge, brought about through some form of structural change or reaction, and the corresponding energy changes. This relationship is examined in four different applications, the first two of which involve the formation of weak to intermediate strength hydrogen bonds. The third application addresses barriers to rotation and inversion and the fourth is an investigation into the hydrolytic cleavage of the P-O-P and P-O-P linkages in "high energy" phosphate molecules. In each case, the energy changes are given in terms of the mechanical properties of the atoms using the theory of atoms in molecules and topological theory of molecular structure.</p> <p>The first application is an investigation into the formation of the hydrogen bonds which result from the dimerization of formamide to its open or cyclic form. It is shown that an important factor governing the changes in the relative stabilities of the atoms on forming the dimers are the opposing flows of σ and π density through the conjugated N-C-O fragments.</p> <p>The weak hydrogen bonded complexes studied in the second application include the Van der Waals complexes NeHCl, NeHF, ArHCi, ArHF and the progressively stronger interactions found in NNHCN, NNHCl, NNHF, HCNHCN, HCNCCl and HCNHF. These weak interactions, which result from the mutual penetration of the non-bonded Van der Waals radii of the H atom of the acid and the terminal base atom, involve little charge transfer between the base and the acid but do result in charge reorganization within reactants. The principal source of the molecular dipole moment enhancement is show to originate from internal polarization of the base atom in the Van der Waals complexes and from the intramolecular charge transfer which occurs between the acid and base fragments for the remaining complexes.</p> <p>The weak hydrogen bonded complexes studied in the second application include the Van der Waals complexes NeHCl, NeHF, ArHCl, ArHF and the progressively stronger interactions found in NNHCN, NNHCl, NNHF, HCNHCN, HCNHCl and HCNHF. These weak interaction, which result from the mutual penetration of the non-bonded Van der Waal's radii of the J atom of the acid and the terminal base atom, involve little charge transfer between the base and the acid but do result in charge reorganization within the reactants. The principal source of the molecular dipole moment enhancement is show to originate from internal polarization of the base atom in the Van der Waals complexes and from the intramolecular charge transfer which occurs between the acid and base fragments for the remaining complexes.</p> <p>The third application addresses barriers to internal rotation and inversion through the relative changes in the attractive and repulsive potential energies using the virial theorem. The rotation barriers in ethane, methanol and methylamine are found to result from an increase in the attractive potential energies in spite of a decrease in the repulsive potential energy, while just the opposite s found for the inversion barriers in NH₃. PH₃, and H₃O+ and for the barrier to bending in H₂O.</p> <p>The atomic and group contributions to the overall hydrolysis reaction energies of the neutral and charged forms of diphosphoric acid, methyldiphosphate and phosphoenolpyruvate are determined in the final application. The stabilizing effects of solvation are shown to be important in the reactions which involve charge separation.</p>