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The [2+2] cycloreversion of silacyclobutane (SCB) and its two methyl-substituted derivatives, 1-methyl-1-silacyclobutane (MSCB) and 1,1-dimethyl-1-silacyclobutane (DMSCB), were studied using ab initio quantum chemistry calculations. The second-order Moller-Plesset (MP2) perturbation theory, complete active space self-consistent field (CASSCF), and coupled clusters methods were used to explore both the concerted and the stepwise cycloreversions of the three molecules. In addition to the orbital symmetry-forbidden supra-supra [2s+2s] transition state, a new orbital symmetry-allowed supra-antara [2s+2a] transition state was discovered for the concerted route for all three molecules. Both methyl substitution and temperature play a role in the kinetic competition between the [2s+2s] and [2s+2a] routes. At 0 and 298 K, the concerted [2s+2a] cycloreversion is kinetically more favorable than the [2s+2s] cycloreversion for SCB, but the opposite is true for MSCB and DMSCB. With increasing temperatures to above 600 and 1800 K, the [2s+2a] cycloreversion becomes more favorable for MSCB and DMSCB, respectively. The methyl substitutions on Si atoms also affect the stability of the diradical intermediate formed by Si-C bond rupture, leading to a less stable diradical with increasing methyl groups.

Pharmaceutical compounds are emerging contaminants that have been detected in surface water across the world. Because conventional wastewater treatment plants are not designed to treat such pollutants, new technologies are needed to degrade and oxidize such contaminants. The newly developed oxy-cracking process was utilized to treat the antidiabetic drug, metformin. The process, which involved partial oxidation of metformin in alkaline aqueous medium, proved to decompose the drug into small organic molecules, with minimum emission of CO2, therefore, increasing its biodegradability and removal from industrial treatment plants. The reaction gaseous products were probed by online gas chromatography. The liquid phase before and after oxy-cracking was analyzed for total carbon content by TOC and gas chromatography mass spectrometry. The products formed from the nitrogen-rich drug included ammonia, amines, amidines, and urea derivatives. A reaction mechanism for the oxy-cracking process is proposed. Because the hydroxyl radical (˙OH) is believed to play a central role in the oxy-cracking process, the mechanism is initiated by ˙OH attacks on metformin, followed by single decomposition or isomerization steps into stable products. The reactions were investigated using density functional theory calculations and validated using high quality 2nd order Moller–Plesset perturbation theory energy calculations.

An efficient method for the preparation of crystalline tantalum carbide (TaC) was reported using a new methyl-substituted precursor, 1-methylsilacyclobutane (MSCB), in the hot-wire chemical vapor deposition process with a tantalum filament. The ability of MSCB to produce methyl radicals on heated Ta filament allows for the formation of crystalline TaC (cubic Fm -3 m ) in a wide temperature range of 1600–2200 °C. This corroborates the key role of the radical species formed via the precursor's decomposition on the hot metal wire in the type of metal alloys formed on the wire surface. The growth rate of TaC achieved at 0.12 μm/min and 0.35 μm/min, respectively, for 1600 °C and 2200 °C is much higher than the value obtained from using CH 4 /H 2 mixtures as the C-containing precursor. Crystalline ditungsten carbide (W 2 C) was formed by treating the tungsten filament with MSCB at the relatively high temperatures of 2200–2400 °C, with a deposition rate of 2.1 μm/min at 2400 °C. The method reported in this work is a useful method to produce crystalline TaC or W 2 C without the use of the corrosive metal halide precursors.

The drug metformin is the most prescribed drug to treat type II diabetes and has been recently reported to have anticancer activities. Because of its wide use, its potential risk on the environment is extremely concerning. In this study, the mechanism and the thermodynamics of the thermo-oxidative decomposition of the metformin were investigated as part of a new solution for the pharmaceutical contamination of water bodies. Thermogravimetry and mass spectrometry were used to demonstrate the metformin thermo-oxidative decomposition under air in the temperature range 25–800 °C. The isoconversional methods of Kissinger-Akahira Sunose (KAS) and Friedman (FR) were implemented to deduce the trends of effective activation energies. As expected, the effective activation energy (Eα) of the reaction was dependent on the reaction temperature, suggesting multi-step reactions. The Eα ranged from 100 to 145 kJ/mol and 200–300 kJ/mol for the KAS and FR methods, respectively. The kinetic triplet, Aα, ΔS‡, and ΔG‡ were also determined by finding the appropriate reaction model. Theoretical calculations were implemented to propose a full reaction mechanism. The oxidation of metformin was investigated with both molecular O2(t) and atomic O(t) oxygen. The experimental results were then explained under the light of the computational data to explain the variation of Eα with temperature, and the competition between the O2(t)/O(t) species.

In this study, the thermal oxidation of an asphaltene model molecule, Quinolin-65, was investigated using the density functional theory (DFT) and the second-order Moller–Plesset (MP2) perturbation theory. The reactions studied involved thermal decompositions as well as the interactions between the model molecule and singlet atomic (O1D) and molecular (O21Δ) oxygen. The theoretical study was performed under conditions similar to those of the uncatalyzed thermal oxidation of asphaltenes. A new reaction pathway for the loss of the olefin chain in Quinolin-65 via a 1,3-hydrogen shift mechanism was revealed. Thermogravimetric analysis of Quinolin-65 was also performed and the reaction products were probed by a mass spectrometer. Both the theoretical study and the thermogravimetric analysis concluded that the thermo-oxidative decomposition of Quinolin-65 is a complex multi-step reaction process, which involves different reaction pathways. The thermodynamic parameters obtained in this study showed that the reaction process should start with the loss of the olefin chain in the Quinolin-65 molecule, followed by the oxidation of the aromatic chain, to produce mainly, H2O, CO2, and SO2.

The reaction kinetics of the decomposition of 1-methylsilacyclobutane (MSCB) in a hot wire chemical vapor deposition (HWCVD) reactor was investigated. The stable reaction products were monitored using vacuum ultraviolet laser single photon ionization in tandem with time-of-flight mass spectrometry. Steady-state approximation was used to determine the rate constants of three individual decomposition pathways of MSCB, i.e., cycloreversion to form ethene and methylsilene (R1), ring opening to form propene and methylsilylene (R2), and exocyclic Si-CH3 bond cleavage to form ˙CH3 radicals (R3). The activation energies (Ea) for R2 and R3 in a HWCVD reactor were determined to be 86.6 kJ mol-1 and 106 kJ mol-1, respectively. The fact that these Ea values are close to those obtained for the MSCB decomposition on metal surfaces under collision-free conditions indicates that the heterogeneous reactions on the hot wire surface govern the gas-phase reaction kinetics in the HWCVD reactor. In addition, the Ea values obtained from a theoretical study of the decomposition kinetics using ab initio calculations at the CCSD(T)/6-311++G(3d,2p)//MP2/6-311++G(d,p) level were 62.9 kcal mol-1 (i.e., 263 kJ mol-1), 62.0 kcal mol-1 (i.e., 259 kJ mol-1), and 86.2 kcal mol-1 (i.e., 361 kJ mol-1) for R1, R2, and R3, respectively. The much lower experimental Ea values compared with those from the theoretical calculations clearly suggest that the tungsten filament in the HWCVD reactor catalyzed the decomposition.

In this study, two dicationic asymmetrical diamine/copper(II) nitrate salt complexes of the general formula trans-[CuII(NN')(2)center dot H2O](NO3)(2) were successfully synthesized using N,N-dimethylethylenediamine and N,N-diethylethylenediamine as asymmetrical diamine ligands. The structure of complex 2 was identified by X-ray single crystal diffraction analysis confirming that the bidentate ligand N,N-dimethylethylenediamine forms a penta-coordinated complex with an H2O molecule located around the copper(II) ion in a trans configuration. It was found that the metal centre is coordinated in a distorted square pyramidal fashion with a tau value of 0.274. The desired complexes were fully characterized using, MS, UV-Vis, CV, FTIR, TG/DTA, and Hirshfeld surface computational analysis. High level theoretical calculations were also performed in order to investigate the complexes structure, conformers, vibrational frequencies, and their excited states., The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for funding this Research group NO (RG -257-1436-1437). The authors are also grateful to the Western Canada Research Grid., info:eu-repo/semantics/publishedVersion