Showing papers by "Thomas Bally published in 2010"
TL;DR: The preparation and characterization of a stable [4]circulene is reported and the trivial name quadrannulene (Latin: quadra, square; annula, ring) for the parent is suggested, abbreviated TMS4-TBQ, which Hopf and co-workers recently summarized two synthetic strategies to the quadrANNulene core.
Abstract: The presence of nonhexagonal rings in an otherwise graphitic lattice induces curvature. Pentagons are common—twelve pentagons surrounded by hexagons make up C60. Larger rings are present in Stone–Wales defects, and the polyhedral formula of Euler mandates their existence in carbon nanotube Y-junctions. Except for a single, partially saturated example, four-membered rings in graphitic structures are, however, unknown. The smallest examples of these graphitic structures are the [n]circulenes, wherein a central n-sided polygon is surrounded by n-fused benzenoid rings. [7]Circulene, first prepared by Yamamoto, Nakazaki, and coworkers in 1983, is saddle shaped. [6]Circulene, or coronene, is the trivial, planar case, and it was first synthesized by Scholl andMeyer in 1932 but also occurs naturally. [5]Circulene, or corannulene, comprises 1/3 of the C60 skeleton and has been intensely studied, and it was first prepared by Lawton and Barth in 1971. Whereas a few pioneering attempts have been reported, [4]circulene has never been synthesized before. We report herein the preparation and characterization of a stable [4]circulene. By analogy with Lawton s naming of corannulene (Latin: cor, heart; annula, ring), we suggest the trivial name quadrannulene (Latin: quadra, square; annula, ring) for the [4]circulene parent. Hence, we name this derivative 1,8,9,16-tetrakis(trimethylsilyl)tetra-cata-tetrabenzoquadrannulene, abbreviated TMS4-TBQ. The IUPAC name and atom numbering are given in the Supporting Information. Our unoptimized five-step synthesis (Scheme1) provides TMS4-TBQ in very low yield. Hopf and co-workers recently summarized two synthetic strategies to the quadrannulene core: making the four-membered ring from [2,2]-paracyclo-
84 citations
TL;DR: A novel example of electromerism, where molecules that are not conventional isomers but instead differ in how the electrons are distributed across their structure are demonstrated.
Abstract: Electromerism is an unfamiliar concept to many chemists and refers to molecules that are not conventional isomers but instead differ in how the electrons are distributed across their structure. A novel example of such electromers has now been demonstrated.
73 citations
TL;DR: This work provides strong support for the Heilbronner-Wiberg interpretation of the vibrational structure in the photoelectron spectrum of 1 in terms of vibronic coupling.
Abstract: The [1.1.1]propellane radical cation 1•+, generated by radiolytic oxidation of the parent compound in argon and Freon matrices at low temperatures, undergoes a spontaneous rearrangement to form the distonic 1,1-dimethyleneallene (or 2-vinylideneallyl) radical cation 3•+ consisting of an allyl radical substituted at the 2-position by a vinyl cation. In similar matrix studies, it is found that the isomeric dimethylenecyclopropane radical cation 2•+ also rearranges to 3•+. The unusual molecular and electronic structure of 3•+ has been established by the results of ESR, UV−vis, and IR spectroscopic measurements in conjunction with detailed theoretical calculations. Also of particular interest is an NIR photoinduced reaction by which 3•+ is cleanly converted to the vinylidenecyclopropane radical cation 4•+, a process that can be represented in terms of a single electron transfer from the allyl radical to the vinyl cation followed by allyl cation cyclization. The specificity of this photochemical reaction provi...
21 citations
TL;DR: Several routes for the synthesis of m-terphenyl thio-, seleno-, and telluroethers were investigated and certain of these compounds showed atropisomerism and barriers for interconversion of isomers were determined by variable-temperature NMR spectroscopy.
Abstract: Several routes for the synthesis of m-terphenyl thio-, seleno-, and telluroethers were investigated m-Terphenyl iodides react with diphenyl diselenides or ditellurides (CsOH·H(2)O, DMSO, 110 °C) to give the desired compounds in 19-84% yield which significantly extends the previously reported such reactions because o-benzyne cannot be an intermediate as previously suggested However, the most general synthetic route was that involving reaction of 2,6-diaryl Grignard reagents with sulfur, selenium, or tellurium electrophiles The m-terphenyl thio-, seleno-, and telluroethers were characterized spectroscopically and, in one case, by single-crystal X-ray analysis Certain of these compounds showed atropisomerism and barriers for interconversion of isomers were determined by variable-temperature NMR spectroscopy The barriers for interconverting the syn and anti atropisomers increase on going from the analogous S to Se to Te compounds Calculations on this isomerization revealed that the barriers are due to rotation about the aryl-aryl bond and that the barriers for rotation about the aryl-chalcogen bond are much lower
19 citations
TL;DR: The primary products, i.e., the radical cations and radicals obtained on oxidation of the glucobrassicin metabolites, indole-3-carbinol (I3C) and diindolylmethane (DIM), and those from parent indole (I) are characterized in an ionic liquid and in Ar matrices.
Abstract: The primary products, i.e., the radical cations and radicals obtained on oxidation of the glucobrassicin metabolites (and dietary supplements), indole-3-carbinol (I3C) and diindolylmethane (DIM), and those from parent indole (I) are characterized in an ionic liquid and in Ar matrices. The radical cations of I and I3C are stable toward (photo)deprotonation under these conditions, but the resulting radicals can be generated by UV-photolysis of the neutral precursors. Two types of radicals, obtained by loss of hydrogen from N- and C-atoms, respectively, are found for I3C and DIM.
15 citations
TL;DR: DFT calculations on 1-trimethylsilyloxybicyclo[4.1.0]heptane show that cleavage of the endocyclic rather than the lateral C-C(OTMS) bond leads to interesting conformational changes which are explored in detail.
Abstract: In contrast to the structurally and configurationally stable alkyl- or aryl-substituted cyclopropyl radical cations, cyclopropyl silyl ethers undergo spontaneous ring opening upon oxidation whereby the endocyclic C-C(OTMS) bond is cleaved with remarkable selectivity. DFT calculations on 1-trimethylsilyloxybicyclo[4.1.0]heptane show that this selectivity arises from the topology of the potential surface of the corresponding radical cation which is initially generated in a very steep region of the potential surface from where the steepest descent leads to cleavage of the endocyclic rather than the lateral C C(OTMS) bond. Cleavage of the lateral bond leads to interesting conformational changes which are explored in detail.
5 citations
1 citations
TL;DR: In this paper, radiolytic ionization of o-methylacetophenone in low temperature matrices, the radical cation of the corresponding enol is formed, and the kinetics of this process indicate a significant contribution of quantum-mechanical tunnelling in the hydrogen atom transfer.
Abstract: Upon radiolytic ionization of o-methylacetophenone in low temperature matrices, the radical cation of the corresponding enol is formed. The kinetics of this process indicate a significant contribution of quantum-mechanical tunnelling in the hydrogen atom transfer. The same species is also formed by ionizing 1-methyl-1,2-dihydrobenzocyclobutenol but the composition of the rotameric mixture of enol radical cations is different in this case. Analogous experiments with 5,8-dimethyl-1-tetralone demonstrate that enol radical cations are stable in their Z-conformation under cryogenic conditions in contrast to the corresponding neutrals.