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131.
James C. Thompson A.P.Gerald Wright William F. Reynolds 《Journal of fluorine chemistry》1981,17(6):509-529
Consideration of 19F-19F and 29Si-19F coupling constants in a series of organosilicon derivatives containing SiF2 and Si2F4 units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal 19F-19F coupling constants in a number of CSiF2SiF2C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ~ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition 29Si-19F coupling constants appear to fall in quite distinct ranges (1JSiF > 300 Hz, 29 Hz < 2JSiF < 55 Hz, 3JSiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF2 with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi2F5-substituted cyclohexadiene. 相似文献
132.
Molecular dynamics simulations are used to calculate the melting point and some aspects of high-temperature solid-state phase transitions of ammonium nitrate (AN). The force field used in the simulations is that developed by Sorescu and Thompson [J. Phys. Chem. A 105, 720 (2001)] to describe the solid-state properties of the low-temperature phase-V AN. Simulations at various temperatures were performed with this force field for a 4 x 4 x 5 supercell of phase-II AN. The melting point of AN was determined from calculations on this supercell with voids introduced in the solid structure to eliminate superheating effects. The melting temperature was determined by calculating the density and the nitrogen-nitrogen radial distribution functions as functions of temperature. The melting point was predicted to be in the range 445 +/- 10 K, in excellent agreement with the experimental value of 442 K. The computed temperature dependences of the density, diffusion, and viscosity coefficient for the liquid are in good agreement with experiment. Structural changes in the perfect crystal at various temperatures were also investigated. The ammonium ions in the phase-II structure are rotationally disordered at 400 K. At higher temperatures, beginning at 530 K, the nitrate ions are essentially rotationally unhindered. The density and radial distribution functions in this temperature range show that the AN solid is superheated. The rotational disorder is qualitatively similar to that observed in the experimental phase-II to phase-I solid-state transition. 相似文献
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Granular flow: Friction and the dilatancy transition 总被引:1,自引:0,他引:1
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