Department of Chemistry
Master of Science
Part 1 of this thesis deals with the role that it -electron density plays in the formation of it -complexes in electrophilic aromatic substitution. Using commercial and synthetic compounds of varying it-electron density, the fact that % -complexes actually exist in these species was determined by a mass spectral investigation that was designed to monitor alkyl side-chain isomerizaitons. Also, the amount of it-complex was determined for each compound by measuring the amount of alkyl carbenium ion loss in each compound's mass spectrum. Found within the systems was an internal trend showing that the greater the amount of 7t-electron density in the ring, the less it-complex formed. This trend was further studied utilizing a Spartan 3.0 computational system, and all data found was internally consistant with the experimental data. It was found that the compounds with the greatest nelectron density used the excess tc-electron density for greater covalency in the complex. In Part 2, the gas-phase reaction between the ethylene oxide radical cation and neutral ethylene oxide, when performed in the high-pressure source of a tandem mass spectrometer, forms a C4Hg02 radical cation adduct. The collisionally activated dissociation (CAD) mass spectrum of the C4H802 adduct is nearly identical to that of the 1,4-dioxane radical cation. Computational investigations utilizing semi-empirical AMI, MNDO, and PM3 methodologies were invoked to determine the mechanistic pathways involved in the reaction. The most likely mechanism is a step-wise process involving a long-chain distonic radical cation intermediate that subsequently forms a non-distonic cyclic radical ion. A calculated thermodynamic driving force of ca. 10 Kcal/mol exists for the cyclization of the long-chain distonic radical cation. For Part 3, an array of acyclic long-chain distonic radical cations was generated and analyzed by semi-empirical AMI computational methods. In general, an enthalpic driving force for the isomerization of the distonic ions to cyclic non-distonic ions was observed. The enthalpies of the isomerizations were evaluated as a function of chain length, identity of the atom (C, O, N) bearing the radical site, and substitution of the radical and carbenium ion sites. The structures, electron distribution, free spin distribution, and thermodynamic stabilities of the cyclic ions generated upon isomerization of the distonic ions were nearly identical to those formed by direct removal of an electron from the corresponding cyclic neutral precursor.
Whittle, Carl, "Fundamental Investigations of Mechanistic Pathways of Selected Organic Reactive Intermediates" (1997). Masters Theses & Specialist Projects. Paper 360.