Jeffrey L. Broeker

Distinguishihg ionization from sulfur p-type lone pair orbitals and carbon π-molecular orbitals by he I/He II photoelectron spectroscopy

Abstract He I and He II photoelectron spectra of methylthiomethylbenzene (2), 2-(1-nethylethylthio) ethylbenzene (3), 1-naphthalenemethanethiol (4), 1,1-dimethylethylthiobenzene (5), benzenethiol (6), and methylthiobenzene (7) are reported. Comparison of the He I and He II band areas for each compound provide a reliable basis for assigning the bands as due to photoionization from a carbon π-molecular orbital, sulfur p-type lone pair orbital, or mixed orbital.Ionization from a molecular orbital localized on sulfur results in a large decrease in intensity using He II compared with He I as the source relative to ionization from carbon π-molecular orbitals. Mixed orbitals with both sulfur and carbon character also give rise to diminished intensities in the He II versus He I spectra relative to pure carbon orbitais, but proportionately less decrease than pure sulfur orbitais.

Synthesis, crystal, and molecular structures and conformations of naphthot[1,8-b,c]-1,5-dithiocin-1,1-dioxide,-1,5-dioxide,-1,1,5-trioxide and -1.1,5,5-Tetraoxide

Abstract Chemoselective oxidation of the known naphtho[1,8,- b , c -1,5-dithiocin, dithioether 1 , to the corresponding -1,1-dioxide: monosulfone 3, 1,5-dioxide: cis-disulfoxide 4 , or -1,1,5,5-tetraoxide: disulfone 6 can be accomplished with potassium permanganate and a phase transfer catalyst in a two phase system in 66% yield, with sodium metaperiodate in aqueous methanol in 95% yield, or ruthenium tetraoxide in 70% yield, respectively. Oxidation of the known monosulfoxide 2 with potassium permanganate and a phase transfer catalyst in a two phase system also gave monosulfone 3 in 73% yield. The corresponding -1,1,5-trioxide: sulfoxide-sulfone 5 was selectively prepared in quantitative yield by oxidation of the monosulfone 3 with sodium metaperiodate in aqueous methanol. The crystal and molecular structures, and conformations of naphtho[1,8- b , c ]-1,5-dithiocin-1,1-dioxide ( 3 ), -1,5-dioxide ( 4 ), -1,1,5-trioxide ( 5 ), and -1,1,5,5-tetraoxide ( 6 ) were determined by single crystal X-ray analysis. These compounds crystallize in the monoclinic space group P2 1/c with a =13.184(4)A, b =13.182(5)A, c =7.106(l)A, β=104.14(5)°, and Z =4, the orthorhombic space group P bca , with a =17.931(2)A, b =13.108(3)A, c =20.280(4)A, and Z =16, the monoclinic space group P2 1/n with a =9.298(1)A, b =10.264 (2)A, c =13.396(2)A, β=110.06(1)°, and Z =4, and the orthorhombic space group P bca with a =12.258(3)A, b =9.997A, C=20.168A, and 2-8, respectively. The structures were solved by direct methods. Full-matrix least-squares refinement led to conventional R factors of 0.034, 0.046, 0.041, and 0.049, respectively. The conformations of the molecules in the solid state were distorted boat, boat with cis-dlequatorial sulfoxide; boat with equatorial sulfoxide, and the unusual twist conformer, respectively.

Formation of sulfur-centered cation radicals by photofragmentation

Abstract The selected dialkyl dithioethers 1,5-dithiocane, 1,4-dithiepane, 1,4-dithiane, and 2,6-dithiaheptane are readily monoalkylated in nitromethane by tert-butyl O-trifluoromethanesulfonyl-3-hydroxyperoxypropanoate, 6 , to give the corresponding sulfonium salt peresters 2a-c , and 3 in good yield. Laser flash photolysis of these compounds affords the known two-sulfur, three-electron stabilized cation radicals 2a , b , and 5 which were characterized by optical absorption spectroscopy.

Conformationai analysis of naphtho[1,8-b,c]-1,5-dithiocin and its s-oxides in solution

Abstract The conformation and conformational barriers In dithioether 1 : naphtho(1,8- b , c ]-1,5-dithiocin were determined in solution by 1 H and 13 C NMR spectroscopic analysis and AMl semiempirical computations. In solution the chair conformer of dithloether 1 is 0.6 kcal/mol lower in energy than the boat conformer. The barriers for chair-to-chair ring inversion and chair-to-boat conversion in this compound are 8.9 kcal/mol and 7.9 kcal/mol, respectively. Monosulfone 3 , disulfoxide 4 , and sulfoxide-sulfone 5 , adopt the chair conformation in solution in contrast to their boat conformation in the solid state. In solution the chair conformation for 3–5 with equatorial sulfoxides is more stable than either the chair conformation with axial sulfoxides or the boat conformers by at least 1 kcal/mol. The barrier for chair-to-chair ring inversion for monosulfone 3 has been determined to be 10.8 kcal/mol. In solution, disulfone 6 appears to adopt either a boat or chair conformation in contrast to the twist conformation in the solid state. The maximum barrier for ring inversion of 6 is 7 kcal/mol. New evidence for the geometry of the transition state for the ring inversion is presented.

Theoretical studies on transannular S-S interactions in geometrically constrained 1,5-dithiocane derivatives

Abstract Vibronic analysis on naphtho[1,8- b , c ]-1,5-dithiocin ( 10 ) and naphtho[1,8- b , c ]-1,5-dithiocin-1-oxide ( 11 ) using the Hartree-Fock method with the STO-3G basis set shows no evidence for covalent-bond formation in 11 compared with 10 . Thus the transannular interaction in 11 is due to electrostatic interaction and not incipient sulfurane formation. Examination of proposed intermediates in the reaction of 11 to form dication 12 using models and ab initio Hartree-Fock calculations using a 6–31G ∗ basis set provides insight into this reaction. The calculations gave no indication of sulfurane formation.

Ionization potentials of some azoalkanes by photoelectron spectroscopy

Abstract Photoelectron spectra have been obtained for a set of azo compounds consisting of three pairs of cis, trans isomers, seven bridgehead substituted 2,3-diazabicyclo[2.2.2]oct-2-enes (DBOs), and one arylazoalkane. The lowest ionization potentials, which range from 7.83 to 9.21 eV, do not correlate with cis ground state energy or photolability of the DBO derivatives. Vibrational fine structure was observed in three DBOs, allowing verification that the lowest ionization takes place from the antibonding combination of nitrogen lone pairs.