scholarly journals Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

2016 ◽  
Vol 12 ◽  
pp. 716-724 ◽  
Author(s):  
Grzegorz Mlostoń ◽  
Paulina Pipiak ◽  
Heinz Heimgartner
Keyword(s):  
Reaction Mechanisms ◽  
Variable Temperature ◽  
Single Case ◽  
Trimethylsilyl Diazomethane ◽  
Cascade Processes ◽  
Higher Temperature

Reactions of dihetaryl and aryl/hetaryl thioketones with 2-diazopropane, diazoethane, and (trimethylsilyl)diazomethane were studied at variable temperature. The experiments showed that reactions with 2-diazopropane carried out at –75 °C occur mainly via the initially formed, relatively stable 1,3,4-thiadiazolines as products of the [3 + 2]-cycloaddition of the diazo dipole onto the C=S bond. The latter decompose only at higher temperature (ca. −40 °C) to generate thiocarbonyl S-isopropanide. In the absence of the starting thioketone, the corresponding thiiranes and/or ethene derivatives, formed from them via spontaneous desulfurization, are the main products. In contrast, reactions with diazoethane occurred predominantly via initially formed diradicals, which in cascade processes gave sterically crowded 4,4,5,5-tetrahetaryl-1,3-dithiolanes as major products. Finally, the reaction of dihetaryl thioketones with (trimethylsilyl)diazomethane occur smoothly at −75 °C leading to the corresponding 4,4,5,5-tetrahetaryl-1,3-dithiolanes as the exclusive [3 + 2]-cycloadducts formed via a cascade of postulated diradicals. The presence of S or Se atoms in the hetaryl rings is of importance for stabilizing diradical intermediates. Remarkably, in no single case, the ‘head-to-head dimerization’ of aryl/hetaryl and dihetaryl substituted thiocarbonyl ylides was observed.

Variable Temperature Measurement on Operating Pentacene-Based OTFT

2008 ◽  
Vol 1091 ◽  
Author(s):  
Hung-Keng Chen ◽  
Po-Tsun Liu ◽  
Ting-Chang Chang ◽  
S.-L. Shy
Keyword(s):  
Conduction Mechanism ◽  
Variable Temperature ◽  
Electrical Measurement ◽  
Isokinetic Temperature ◽  
Trap States ◽  
Band Tail ◽  
Thermally Activated ◽  
Multiple Trapping ◽  
Higher Temperature ◽  
Release Model

AbstractVariable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer¡VNeldel relationship between the activation energy and the prefactor with a Meyer¡VNeldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.

Application of microelectrodes and variable-temperature techniques to voltammetric studies of inorganic reaction mechanisms

1989 ◽  
Vol 93 (1) ◽  
pp. 1-18 ◽  
Author(s):  
C.D. Baer ◽  
T.F. Camaioni-Neto ◽  
D.A. Sweigart ◽  
A.M. Bond ◽  
T.F. Mann ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
Variable Temperature ◽  
Voltammetric Studies

scholarly journals Temperature-Dependent Accommodation of Two Lattices of Largely Different Size during Growth

Nanomaterials ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 710
Author(s):  
Carsten Sprodowski ◽  
Karina Morgenstern
Keyword(s):  
Low Temperature ◽  
Variable Temperature ◽  
Lattice Misfit ◽  
Scanning Tunneling ◽  
Temperature Structure ◽  
Misfit Dislocations ◽  
Tunneling Microscopy ◽  
Large Lattice ◽  
Higher Temperature ◽  
Temperature Scanning

If a material grows on another material with a largely different lattice constant, which of the two adapts for an energetically favorable growth? To tackle this question, we investigate the growth of Ag on Cu(111) by variable temperature scanning tunneling microscopy. The structures grown between 120 and 170 K are remarkably different from those grown between 200 and 340 K. The low-temperature structure is rectangular-like and consists of stacked rods, 7 to 8 Ag atoms long, which form a superstructure without long-range order. This structure covers the whole surface prior to nucleation of further layers. The high-temperature structure is hexagonal and consists of misfit dislocations forming 8 × 8 to 10 × 10 superstructures. For this structure, second layer nucleation sets in far before the closure of the first monolayer. While both structures are driven by the large lattice misfit between the two materials, the growing Ag layer adapts to the Cu surface at low temperature, while the Cu surface adapts to the growing Ag layer at higher temperature.

Design of Skirt to Cone Joint in Coke Drum: A Parametric Approach Based on Fatigue Analysis

2011 ◽  
Author(s):  
M. Sohel M. Panwala ◽  
S. L. Jaiswal
Keyword(s):  
Fatigue Life ◽  
Thermal Fatigue ◽  
Parametric Study ◽  
Variable Temperature ◽  
Great Influence ◽  
Analysis Tool ◽  
Element Analysis ◽  
Higher Temperature ◽  
Temperature And Pressure ◽  
Transient Thermal

Coke Drums are critical equipment in refineries due to variable temperature and pressure. The temperature is highly fluctuating which causes the thermal fatigue in coke drums. The phenomenon of this thermal fatigue plays a very crucial role in failure of coke drums. In the present study, a coke drum is subjected to pressure - temperature reversal with each cycle of 48 hours duration. Temperature and pressure varies from 338 to 738 K and 0 to 0.404 MPa, respectively. The material of construction is 1.25Cr-0.5Mo (SA-387 Gr. 11 Cl. 1). This coke drum is at higher temperature of 738 K for 24 hours in one full cycle. The skirt to shell and cone junction is a critical portion of coke drum because it is highly susceptible to fatigue at higher temperature. In addition to this, the skirt is provided with slots at specific pitch all around circumference to induce flexibility. This has great influence on fatigue life due to localized stress at higher temperature. API 579-1/ASME FFS-1 2007 is used for the fatigue life evaluation in the present case. Nonlinear transient thermal analysis is coupled with the elastic-plastic structural analysis for calculation of stresses and strains. These stresses are further used for deducing permissible cycles for fatigue as per the approach based on API 579-1. A Parametric study has been carried out in Finite Element Analysis tool ‘ANSYS-12.1’ for different configuration of skirt to cone junction specifically in terms of inside crotch radius. The effect on fatigue life has been studied with variation in inside crotch radius. It has been found that fatigue life at skirt to cone junction is increasing with increase in crotch radius. But, this increase in crotch radius is adversely effects on slot tip where the life is drastically reducing. Such parametric study can be considered for selection of inside crotch radius for given skirt thickness and diameter.

Assessing distortion of the AF 6 − (A=As, Sb) octahedra in solid hexafluorometallates(V) via NMR spectroscopy

2015 ◽  
Vol 93 (9) ◽  
pp. 938-944 ◽  
Author(s):  
Alexandra Faucher ◽  
Victor V. Terskikh ◽  
Roderick E. Wasylishen
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
Solid State Nmr ◽  
Solid Phase ◽  
Variable Temperature ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Cubic Phase ◽  
Solid State Nmr Spectroscopy ◽  
Higher Temperature

Arsenic and antimony hexafluoride salts have played an important role in the history of both solution and solid-state NMR spectroscopy. Here, solid polycrystalline KAsF6 and KSbF6 have been studied via high-resolution variable temperature 19F, 75As, 121Sb, and 123Sb solid-state NMR spectroscopy at high magnetic field (B0 = 21.14 T). Both KAsF6 and KSbF6 undergo solid-solid phase transitions at approximately 375 and 301 K, respectively. We use variable temperature NMR experiments to explore the effects of crystal structure changes on NMR parameters. CQ(75As) values for KAsF6 at 293, 323, and 348 K are −2.87 ± 0.05 MHz, −2.58 ± 0.05 MHz, and −2.30 ± 0.05 MHz, respectively, the sign determined via DFT calculations. In the higher temperature cubic phase, CQ(75As) = 0 Hz, consistent with the crystal symmetry at the arsenic nucleus in this phase. In contrast, CQ values for 121Sb and 123Sb in the cubic phase of KSbF6 are nonzero. E.g., at 293 K, CQ(121Sb) = 6.42 ± 0.10 MHz, and CQ(123Sb) = 8.22 ± 0.10 MHz. In the higher temperature tetragonal phase (343 K) of KSbF6, these values are 3.11 ± 0.20 MHz and 4.06 ± 0.20 MHz, respectively. CASTEP calculations performed on the cubic and tetragonal structures support this trend. Isotropic indirect spin-spin coupling constants are 1J(75As,19F) = −926 ± 10 Hz (293 K) and −926 ± 3 Hz (348 K), and 1J(121Sb,19F) = −1884 ± 3 Hz (293 K), and −1889 ± 3 Hz (343 K). Arsenic-75 and antimony-121,123 chemical shift values show little variation over the studied temperature ranges.

scholarly journals GROWTH RESPONSES OF FIVE NON TOXIC ALEXANDRIUM SPECIES (DINOPHYCEAE) TO TEMPERATURE AND SALINITY

1970 ◽  
Vol 32 (2) ◽  
pp. 189-195
Author(s):  
Po-Teen Lim ◽  
Chui-Pin Leaw ◽  
Shinnosuke Kaga ◽  
Katsushi Sekiguchi ◽  
Takehiko Ogata
Keyword(s):  
Salinity Tolerance ◽  
Variable Temperature ◽  
Culture Conditions ◽  
Temperate Species ◽  
Salinity Range ◽  
Tropical Species ◽  
Optimum Growth ◽  
Growth Responses ◽  
Clonal Cultures ◽  
Higher Temperature

Growth response of five clonal cultures of Alexandrium obtained from tropical and temperate waters were examined. Experiments were carried out in eighteen variable temperature-salinity conditions (temperatures of 15 °C, 20°C, and 25°C; salinities between 5 to 30 psu) under constant illumination of 150 ± 10.0 Amol m-2 s-' at 15:9 light:dark photo-cycle. Our results showed optimum growth of all Alexandrium species at 20 - 25°C. The salinity range for optimum growth however varied among the species. Growth rates of A. eine, A. insuetum, and A. fraterculus (0.28 — 0.37 day') were higher than those of A. leei and A. pseudogoniaulax under the same culture conditions (0.14 —0.22 day-'). The three temperate species showed positive growth at suboptimum temperature, 15°C, but the tropical species did not grow and died off. Salinity tolerance of the five species in decreasing order was A. pseudogoniaulax > A. leei > A. insuetum > A. affine > A. fraterculus. Results of the present study showed vast variations in salinity tolerance among the Alexandrium species regardless the geographical origins. Adaptation of the temperate species at higher temperature indicated that the species might proliferate in warm tropical waters.

Koordination Des Anions Von 2,4-Dicyanoglutaconsäurediethylester An Tripodeisen(Ii)-Einheiten. Die Entstehung Helikaler Strukturen

2001 ◽  
Vol 56 (8) ◽  
pp. 735-746 ◽  
Author(s):  
Volker Jacob ◽  
Gottfried Huttner ◽  
Elisabeth Kaifer ◽  
Peter Kircher
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
Cyano Group ◽  
Sodium Cyanide ◽  
Diethyl Ester ◽  
Bridging Ligands ◽  
Bidentate Chelate ◽  
Glutaconic Acid ◽  
Higher Temperature ◽  
Dynamic Exchange

The anion of 2,4-dicyano glutaconic acid diethyl ester, [NCC(COOEt)CHC(COOEt)CN]- (1- ), as an α,μ;-dinitrile with a three atom spacer is a highly variable ligand capable of binding in a monodentate η1-fashion, in a bidentate chelate fashion, and as a μ2-bridging entity. TripodFe(1)2, 2, [tripod = CH3C(CH2PPh2)3] contains one chelating ligand 1- and one terminally coordinated ligand 1-- . Variable temperature NMR spectroscopy shows, that, while the structure is static at 193 K, dynamic exchange of the donor functions of chelating and terminally bonded ligands occurs at higher temperature. TripodFe(1)2, 2, is obtained from a 1:1:2 mixture of tripod, Fe(II)aq (BF4)2, and Na1-2H2O . With a stoichiometry 1:1:1 of these ingredients and an additional naif equivalent of sodium cyanide, the dinuclear compound [tripodFe{μ-NCC(COOEt)CHC(COOEt)CN}2{μ-CN}Fetripod]BF4, 3 BF4, is obtained. The structure of 3+ shows a helical arrangement of the ligands 1- around the Fe···Fe axis which is a consequence of the incomensurability of the bridging ligands 1- and μ-CN. The two iron centers in 3BF4 differ by their coordination to the carbon or to the nitrogen terminus of the bridging cyano group. This difference is reflected by the NMR spectra, Mössbauer spectra and cyclovoltammograms

The Effect of POSS-NH2 on the Curing Reaction of Cyanate Ester Resin

2011 ◽  
Vol 217-218 ◽  
pp. 274-279 ◽  
Author(s):  
Zeng Ping Zhang ◽  
Jian Zhong Pei ◽  
Shuan Fa Chen ◽  
Hong Zhao Du ◽  
Yong Wen
Keyword(s):  
Reaction Mechanisms ◽  
Catalytic Effect ◽  
Curing Kinetics ◽  
Cyanate Ester ◽  
Cyanate Ester Resin ◽  
Curing Reaction ◽  
Ft Ir ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Different Content

A functional POSS monomer (POSS-NH2) was employed to modify cyanate ester (CE) resin. A series of POSS-NH2/CE hybrids containing different content of POSS have been prepared by melt casting and then curing. The curing kinetics and reaction mechanisms of the resin systems were studied by using FT-IR. The experimental results show that both temperature and POSS content may influence the curing reaction of CE. POSS-NH2 mainly displays the catalytic effect at higher temperature (220oC). While the circumstance is more complex at lower temperature (190oC).

scholarly journals Study on reaction mechanisms of iron matrix compositesreinforced with in situ Al2O3 particles reacted byAl-Fe2O3-Fe system

2018 ◽  
Vol 238 ◽  
pp. 02006
Author(s):  
Chengyan Zhu ◽  
Jie Jiang ◽  
Heguo Zhu
Keyword(s):  
Heating Rate ◽  
Reaction Mechanisms ◽  
Reaction Times ◽  
Matrix Composites ◽  
Dsc Analysis ◽  
Iron Matrix ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Higher Temperature

Iron matrix composites reinforced with Al2O3 particles were fabricated in situ through exothermic dispersive (XD) reaction from a powder mix of pure elements Fe, Al and Fe2O3. The fabrication and reaction mechanisms were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. The reaction between Al and Fe2O3 was found to occur in three steps. Their activation energies are 203.8 kJ/mol, 1100.9 kJ/mol and 380 kJ/mol, respectively. DSC analysis shows that the reaction peak shifts to a higher temperature with an increase in the heating rate. When the heating rate is 10 K/min, the rates of the three reactions exhibit a similar trend, i.e., the reaction rate is very slow at the start, and then it increases rapidly, finally it becomes slow again. Their reaction times are 456, 672 and 650 s, respectively.

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