One objective of this study was to explore the intramolecular [2+2] cycloadditions of phenoxyketenes to carbonyl groups with isoflavones and benzofurans as target compounds. The other objective was to investigate the eyeloaddition reactions of rarely studied aminoketenes. The conversion of 2-(carboxyalkoxy)benzils to the corresponding phenoxyketenes leads to an intramolecular [2+2] cycloaddition to ultimately yield isoflavones and/or 3-aroylbenzofurans. The product distributions are dependent upon the substitution pattern in the original benzil acids. The initial cycloaddition products, β-lactones, are isolated in some instances while some β-lactones spontaneously underwent decarboxylation and could not be isolated. The ketene intermediate was demonstrated in the intramolecular reaction of benzil acids or ketoacids with sodium acetate and acetic anhydride. It is suggested that sodium acetate and acetic anhydride could serve as a source for the generation of ketenes directly from certain organic acids. The treatment of ketoacids with acetic anhydride and sodium acetate provides a simpler procedure to prepare benzofurans than going through the acid chloride with subsequent triethylamine dehydrochlorination to give the ketenes. N-Ary1-N-alkylaminoketenes were prepared for the first time from the corresponding glycine derivatives by using p-toluenesulfonyl chloride and triethylamine. These aminoketenes underwent in situ cycloadditions with cyclopentadiene, cycloheptene and cyclooctenes to yield only the endo -bicyclobutanones. The cycloheptene and cyclooctene cycloaddition products underwent dehydrogenation under the reaction conditions to yield bicycloenamines. A mechanism is proposed for this dehydrogenation involving a radical cation of the arylalkylamine. (N-Phenyl-N-methyl) aminomethylketene was also prepared and found to undergo an intramolecular Friedel-Crafts type acylation to yield an indole derivative when prepared by the acetic anhydride, sodium acetate method. The in situ cycloaddition of N-aryl-N-alkyl aminoketenes with various imines was found to form predominately cis-3-amino-2-azetidinones. A mechanism involving a dipolar intermediate is provided whereby the structure of the intermediate is determined by both electronic and steric effects. The stereochemistry of the resulting β-lactams is dependent upon the structure of the dipolar intermediate.

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The PIXEL method has been used for several years to analyse intermolecular interactions in organic crystals. The simplicity and speed of the calculations, along with the breakdown of intermolecular energies into physical contributing terms, mean that it has had a massive influence on the way organic crystal structures are interpreted. In the work done to date, the parameters required to perform a PIXEL calculation have been established for 1st, 2nd and 3rd row transition metals. Using these parameters, lattice energies of several transition metal complexes containing various chemical environments have been calculated and compared to experimental sublimation enthalpies. Straight line parameters for these results have been comparable to work by Gavezzotti, the author of the program, in testing the method for organic crystal structures. In addition to lattice energies, PIXEL gives dimer interaction energies of molecules in a crystal structure. The values of these interactions have been compared to single point DFT energy calculations. PIXEL has shown good agreement with a range of different intermolecular interactions, along with a significant saving in computer time over the higher level calculations. Aside from four empirical parameters, PIXEL requires only fundamental atomic properties such as ionisation potentials, electronegativities and van der Waals radii. For the most part, these values are obtained from standard reference tables and texts with the exception of atomic polarizabilities. This parameter is of great importance as it is used during the calculation of the dispersion term, an interaction which has a major influence on crystal packing. In previous work, atomic polarizabilities have been calculated using either the Slater-Kirkwood approximation or the Clausius-Mossotti relation. Both of these methods are rather simple, and do not account for possible changes in atomic polarizability resulting from differences in chemical environment. The Atoms in Molecules (AIM) approach has been used to attempt to obtain a range of polarizability values for atoms common to organic chemistry. It is observed that in the series of straight chained primary monoamines, Cn-H2n+3N, an alternation in melting points occurs between odd and even values of n. This alternation could be traced to differences in hydrogen-bonding and chain-packing that occur between odd and even-membered amines. Molecular interaction energy calculations were carried out using the PIXEL method, enabling quantitative energetic analysis of the packing differences. In this work, the crystal structures of the primary amines from ethylamine to decylamine were solved for the first time. All of these compounds are liquids at room temperature, so crystals were grown in situ by laser-assisted zone refinement at 10 K below their melting points. Diffraction data were then collected at 150 K. From propylamine to decylamine, all crystal structures are orthorhombic (or pseudo-orthorhomic) with the unit cell dimensions ~5 Ǻ x ~7 Ǻ x c Ǻ, where c increases with chain length. In the case of ethylamine, a phase characterised by single crystal diffraction at 180 K underwent a transition to a different phase on cooling to 150 K. The low-temperature phase was investigated using powder methods.

Noncovalent intermolecular interactions, widely found in molecular clusters and bio-molecules, play a key role in many important processes, such as phase changes, folding of proteins and molecular recognition. However, accurate calculation of interaction energies is a very difficult task because the interactions are normally very weak. Rigorous expressions for the electrostatic and polarization interaction energies between two molecules A and B, in term of the electronic densities, have been programmed: (see formula in document). Z is atomic charge, ρ0 is the electron density of the isolated molecule and Δρind is the electron density change of the molecule caused by polarization. With some approximations, procedures for electrostatic and polarization energy calculations were developed that involve numerical integration. Electrostatic and polarization energies for several bimolecular systems, some of which are hydrogen bonded, were calculated and the results were compared to other theoretical and experimental data. A second method for the computing of intermolecular interaction energies has also been developed. It involves a “supermolecule” calculation for the entire system, followed by a partitioning of the overall electric density into the two interacting components and then application of eq. (1) to find the interaction energy. In this approach, according to Feynman’s explanation to intermolecular interactions, all contributions are treated in a unified manner. The advantages of this method are that it avoids treating the supersystem and subsystems separately and no basis set superposition error (BSSE) correction is needed. Interaction energies for several hydrogen-bonded systems are calculated by this method. Compared with the result from experiment and high level ab initio calculation, the results are quite reliable.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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The London dispersion interaction is responsible for attraction between non-polar molecules and is of great importance in describing structure and reactivity in many areas of chemistry. Dispersion is difficult to model accurately. Density Functional Theory (DFT) methods, widely used in computational chemistry today, do not include the necessary physics. This often leads to qualitatively incorrect predictions when DFT is applied to dispersion-bound systems. A novel DFT method has been developed which is capable of accurately modeling dispersion. Dispersion attraction between molecules arises when an instantaneous dipole moment in one molecule induces a dipole moment in a second molecule. Our approach proposes that the source of these instantaneous dipole moments is the position-dependent dipole moment of the exchange hole. The model is no more computationally expensive than existing DFTs and gives remarkably accurate dispersion coefficients, intermolecular separations, intermolecular binding energies, and intramolecular conformational energies. Our dispersion theory is also combined with previous post-exact-exchange models of dynamical and nondynamical correlation, yielding a unified exact-exchange-based energy functional called DF07. DF07 overcomes many of the outstanding problems in DFT arising from local exchange approximations. The DF07 model is shown to provide highly accurate results for thermochemistry, kinetics, and van der Waals interactions. / Thesis (Ph.D, Chemistry) -- Queen's University, 2007-11-29 21:57:09.045

Thesis (M.S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2005. / Kubanek, Julia, Committee Member ; Collard, David, Committee Member ; Shuker, Suzanne, Committee Chair. Includes bibliographical references.