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81.
Tom E. Stennett Arumugam Jayaraman Tobias Brückner Lea Schneider Holger Braunschweig 《Chemical science》2020,11(5):1335
Five compounds containing boron–boron multiple bonds are shown to undergo hydrophosphination reactions with diphenylphosphine in the absence of a catalyst. With diborenes, the products obtained are highly dependent on the substitution pattern at the boron atoms, with both 1,1- and 1,2-hydrophosphinations observed. With a symmetrical diboryne, 1,2-hydrophosphination yields a hydro(phosphino)diborene. The different mechanistic pathways for the hydrophosphination of diborenes are rationalised with the aid of density functional theory calculations.Compounds containing boron–boron double and triple bonds are shown to undergo uncatalysed hydrophosphination reactions with diphenylphosphine. 相似文献
82.
PDDG/PM3 and PDDG/MNDO: improved semiempirical methods 总被引:1,自引:0,他引:1
Two new semiempirical methods employing a Pairwise Distance Directed Gaussian modification have been developed: PDDG/PM3 and PDDG/MNDO; they are easily implemented in existing software, and yield heats of formation for compounds containing C, H, N, and O atoms with significantly improved accuracy over the standard NDDO schemes, PM5, PM3, AM1, and MNDO. The PDDG/PM3 results for heats of formation also show substantial improvement over density functional theory with large basis sets. The PDDG modifications consist of a single function, which is added to the existing pairwise core repulsion functions within PM3 and MNDO, a reparameterized semiempirical parameter set, and modified computation of the energy of formation of a gaseous atom. The PDDG addition introduces functional group information via pairwise atomic interactions using only atom-based parameters. For 622 diverse molecules containing C, H, N, and O atoms, mean absolute errors in calculated heats of formation are reduced from 4.4 to 3.2 kcal/mol and from 8.4 to 5.2 kcal/mol using the PDDG modified versions of PM3 and MNDO over the standard versions, respectively. Several specific problems are overcome, including the relative stability of hydrocarbon isomers, and energetics of small rings and molecules containing multiple heteroatoms. The internal consistency of PDDG energies is also significantly improved, enabling more reliable analysis of isomerization energies and trends across series of molecules; PDDG isomerization energies show significant improvement over B3LYP/6-31G* results. Comparison of heats of formation, ionization potentials, dipole moments, isomer, and conformer energetics, intermolecular interaction energies, activation energies, and molecular geometries from the PDDG techniques is made to experimental data and values from other semiempirical and ab initio methods. 相似文献
83.
Ming LC Sharma SK Jayaraman AJ Kobayashi Y Suzuki E Endo S Prakapenka V Yang D 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(10):2418-2422
Both X-ray diffraction and Raman spectroscopy measurement were carried out on the same powder sample of CuGeO(3)(III) in a diamond anvil cell to high pressures at room temperature. The phase transformation of (III)-(IV) phase was observed at about 7GPa with both methods and the results were also in accord with previous powder diffraction and Raman measurements, respectively. However, the powder diffraction data were strikingly different from those reported in a recent single-crystal study on the phase (III). It is, therefore, evident that the phase transformations in CuGeO(3)(III) would be as complicated as those in CuGeO(3)(I) and that the monoclinic phase obtained from single-crystal phase (III) at approximately 7GPa is not the phase (IV) previously observed but rather a new phase (IVa) in CuGeO(3). 相似文献
84.
We describe a simulation method to design surfaces for recognizing specific monomer sequences in copolymers. We fix the monomer sequence statistics of the AB copolymers on a surface containing two types of sites and allow the simulation to iterate towards an optimal surface pattern that can recognize and selectively adsorb the sequence in the copolymer. During the simulation the surface pattern is designed by switching identities of two randomly picked sites. For copolymers with less blocky sequences the designed surfaces recognize the correct sequence well when the segment-surface interactions dominate over the intersegment interactions. For copolymers with more blocky sequences recognition is good when the segment-surface interactions are only slightly stronger than the intersegment interactions. 相似文献
85.
Juan G. Andrade Jayaraman Chandrasekhar Paul Von Ragu Schleyer 《Journal of computational chemistry》1981,2(2):207-211
Molecular orbital calculations on the C4H2 potential energy surface indicate singlet trialene (1) not only to be thermodynamically unstable, but also to have negligible barriers to interconversion to diacetylene. 相似文献
86.
K.H. Bray Mahavir jain K.S. Jayaraman G. LobiancoG.A. Moss W.T.H. Van OersD.O. Wells 《Nuclear Physics A》1972
The elastic and inelastic scattering of protons from 6Li has been studied at incident energies of 25.9, 29.9, 35.0, 40.1 and 45.4 MeV. The 2.18 MeV (3+, T = 0) first excited state of 6Li was found to be strongly excited, but the 3.56 MeV (0+, T = 1) second excited state was quite weakly excited. Angular distributions for excitation of the 2.18 MeV level were measured at all five energies, while angular distributions for excitation of the 3.56 MeV level were extracted only at 25.9 and 45.4 MeV. To test the applicability of the optical model for the scattering of protons from such a light nucleus the elastic scattering angular distributions have been analyzed using the eleven-parameter search code SEEK. Available polarization angular distributions were included in the analysis. Reasonable fits to the data have been obtained with an average geometry potential. Theoretical estimates of the real part of the optical potential and the inelastic scattering differential cross sections have been made using the microscopic model for proton-nucleus scattering. Both phenomenological and realistic forces have been considered and the necessary nuclear transition densities have been extracted from experimental elastic and inelastic electron scattering data. An estimate of a possible spin-spin term in the optical potential has also been made. 相似文献
87.
1,2-Hydride shift barriers in classical carbenium ions increase with decreasing ring size; this can be attributed to the increased strain of the H bridged structures in the small rings. 相似文献
88.
Sm4Bi3 has the anti-Th3P4 (cubic) structure with three Sm2+ ions and one Sm3+ ion. The compound undergoes a first-order, isostructural transition at about 26 kbar. The resistance abruptly decreases by a factor of three and the volume by about 10%. The Sm2+ ions undergo a change towards the 3+ state in the transition and the material goes from semimetallic to a metallic state. The behavior of the resistance anomaly suggests termination of the phase boundary at a critical point. 相似文献
89.
We report the existence of a volume collapsed strongly mixed valent state at pressures above 65 K bars in the prototype “concentrated Kondo” system CeAl2 and discuss the relevant energy scales and general phase diagram of CeAl2. To our knowledge this is the first demonstrated example of what should be a large class of systems exhibiting the full diversity of ground states of an Anderson lattice. 相似文献
90.