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William T. G. Johnson David A. Hrovat Anne Skancke Weston Thatcher Borden 《Theoretical chemistry accounts》1999,102(1-6):207-225
Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl find that the singlet
lies well below the triplet. The C
2 singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure
of ΔH
‡
298 = 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated
to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the
transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy.
Received: 2 July 1998 / Accepted: 4 August 1998 / Published online: 16 November 1998 相似文献
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Dr. Sharifa Hussein Denis Priester Paul Beet Dr. Jonathon Cottom Sam J. Hart Tim James Dr. Robert J. Thatcher Dr. Adrian C. Whitwood Dr. John M. Slattery 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(9):2262-2271
The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor PIII ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor PIII ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of PIII ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3−n, where R=Ph, RF=C(H)(CF3)2 and C(CF3)3; n=1–3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands. 相似文献
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In accord with experiment, DFT calculations find that cyclooctatetraene (COT, 1a) is lower in energy than its valence isomer, bicyclo[4.2.0]octa-2,4,7-triene (BCOT, 3a) and that the iron tricarbonyl complex of COT [COT-Fe(CO)(3), 2a] is lower in energy than the iron tricarbonyl complex of BCOT [BCOT-Fe(CO)(3), 4a]. Also in agreement with experiment are the DFT findings that 1,3,5,7-tetramethylCOT (TMCOT, 1b) is lower in energy than 1,3,5,7-tetramethylBCOT (TMBCOT, 3b), but that the iron tricarbonyl complex of TMCOT [TMCOT-Fe(CO)(3), 2b] is higher in energy than the iron tricarbonyl complex of TMBCOT [TMBCOT-Fe(CO)(3), 4b]. Calculations of the energies of isodesmic reactions allow the effect of each of the four methyl groups in 1b-4b to be analyzed in terms of its additive contribution to the relative energies of TMCOT (1b) and TMBCOT (3b) and to the Fe(CO)(3) binding energies in TMCOT-Fe(CO)(3) (2b) and TMBCOT-Fe(CO)(3) (4b). Our calculations also predict that the eight methyl groups in octamethylCOT-Fe(CO)(3) [OMCOT-Fe(CO)(3), 2c] should have much more than twice the effect of the four methyl groups in TMCOT-Fe(CO)(3) (2b) on raising the energy of OMCOT-Fe(CO)(3) (2c), relative to that of OMBCOT-Fe(CO)(3) (4c). The effects of the interactions between the methyl groups in OMCOT-Fe(CO)(3) (2c) and OMBCOT-Fe(CO)(3) (4c) are dissected and discussed. 相似文献
68.
Borden WT 《The Journal of organic chemistry》2011,76(9):2943-2964
Over the past 40 years, much of the author's research, both computational and experimental, has involved collaborations. This Perspective describes some of the author's collaborative research in eight different areas of organic and theoretical chemistry: (1) hydrocarbons containing unsaturatively, 1,3-bridged cyclobutane rings, (2) the use of orbital topology for predicting the ground states of diradicals, (3) violations of Hund's rule, (4) the chemistry of phenylnitrenes, (5) tunneling by carbon in organic reactions, (6) the Cope rearrangement and the effect of substituents on it, (7) pyramidalized alkenes, dehydrocubanes, cubyl cation, and octanitrocubane, and (8) the effects of geminal fluorine substitution at C-2 of 1,3-diradicals. Highlighted in this Perspective are the synergism between calculations and experiments in the author's research and the many different roles that serendipity has played in the collaborations that are described herein. 相似文献
69.
Takatoshi Ichino Dr. Stephanie M. Villano Dr. Adam J. Gianola Dr. Daniel J. Goebbert Dr. Luis Velarde Dr. Andrei Sanov Prof. Stephen J. Blanksby Dr. Xin Zhou Dr. David A. Hrovat Dr. Weston Thatcher Borden Prof. W. Carl Lineberger Prof. 《Angewandte Chemie (International ed. in English)》2009,48(45):8381-8381
70.
Jonathan J. Stickel Jeffrey S. Knutsen Matthew W. Liberatore Wing Luu Douglas W. Bousfield Daniel J. Klingenberg C. Tim Scott Thatcher W. Root Max R. Ehrhardt Thomas O. Monz 《Rheologica Acta》2009,48(9):1005-1015
The conversion of biomass, specifically lignocellulosic biomass, into fuels and chemicals has recently gained national attention
as an alternative to the use of fossil fuels. Increasing the concentration of the biomass solids during biochemical conversion
has a large potential to reduce production costs. These concentrated biomass slurries have highly viscous, non-Newtonian behavior
that poses several technical challenges to the conversion process. A collaborative effort to measure the rheology of a biomass
slurry at four separate laboratories has been undertaken. A comprehensive set of rheological properties were measured using
several different rheometers, flow geometries, and experimental methods. The tendency for settling, water evaporation, and
wall slip required special care when performing the experiments. The rheological properties were measured at different concentrations
up to 30% insoluble solids by mass. The slurry was found to be strongly shear-thinning, to be viscoelastic, and to have a
significant concentration-dependent yield stress. The elastic modulus was found to be almost an order of magnitude larger
than the loss modulus and weakly dependent on frequency. The techniques and results of this work will be useful to characterize
other biomass slurries and in the design of biochemical conversion processing steps that operate at high solids concentrations. 相似文献