Synthetic and computational studies on organosulfur radical cations and alpha-metalated sulfides
AuthorLorance, Edward Donald
AdvisorGlass, Richard S.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe oxidation potentials and electrooxidation mechanism of 3,6-di substituted-1,2-dichalcogenins was investigated by cyclic voltammetry. An EC mechanism was found experimentally and the basis for the chemical step was found computationally to be a change in the planarity of the ring on electron transfer. Photoelectron spectra were obtained of 3,6-disubstituted-1,2-dichalcogenins a different ionizing photon energies. The interpretation of the photoelectron spectra was assisted by computational simulation. A narrow ionization band was found, and was assigned as the sulfur-sulfur σ orbital by computation and comparison of ionization cross-sections. Computational simulation of the excited state determined that this orbital is paired with a low-energy σ* orbital. Electronic transitions to the σ* orbital were found to be common in disulfides, and the low energy of the σ* orbital in 1,2-dichalcogenins causes their unusual color. The computed geometry of the excited state, coupled with ¹H NMR and ⁷⁷Se NMR data, also provided evidence of the limited anti-aromaticity of 1,2-dithiins. A systematic study of the α-deprotonation of dialkyl sulfides was made with Lochmann's/Schlosser's base. The products were analyzed by GC/MS, and the extent of both deprotonation and decomposition was assessed. Mechanisms of decomposition were evaluated. 4-tert-Butylthiane was alpha-deprotonated and stannylated in good yield, in a 38:1 cis:trans ratio. The oxidation potentials of various α-stannylated dialkyl sulfides were analyzed by cyclic voltammetry. The dependence of oxidation and ionization potential on the C-S-C-Sn dihedral angle was investigated computationally, and was found to obey a Karplus-Barfield-type relationship, with an ionization potential minimum near 90°. The computational predictions were borne out in the oxidation potential of cis-2-trimethylstannyl-4-tert-butylthiane (1.17 V), which was found to be slightly lower than the underivatized sulfide but much higher than other alpha-stannylated sulfides due to the 180°C-S-C-Sn dihedral angle. Various computational techniques were used to find evidence of the cyclic interaction of p-type lone pair orbitals in tetrathiatetraasterane. The neutral species and the radical cation were computationally predicted to be possess the same symmetry (D₄(h)) and cyclic interaction of sulfur lone pair orbitals, but oxidation to the dication was predicted to break a carbon-carbon bond.
Degree ProgramGraduate College