In this paper, the kinetics of the thermal decomposition reaction of 3,3,6,6-tetramethyl-1,2,4,5 tetroxane (ACDP) is investigated in various oxygen solvents at different temperatures. Linear relationships are observed between the enthalpy and entropy of activation of the unimolecular reactions of those diperoxides. The isokinetic temperature calculated by Leffler’s treatment is 527.2K, which is consistent with the proposed Exner correlation between the logarithm of the rate constant values for the same reaction in each solvent at two temperatures, where the corresponding ß value was 523.5K. A true “isokinetic relationship” for the ACDP thermolysis indicates that their reactions constitute a reaction series with similar interaction mechanisms. This can be related to the capacity for hydrogen bonding between the solvent and the diperoxide molecules. The solvanting properties of the media help the peroxidic bond rupture these molecules.
Cyclic organic peroxides are a broad and highly sought-after class of peroxide compounds that present high reactivity and even explosive character. The unusually high reactivity of these peroxides can generally be attributed to the rupture of O-O bonds. Cyclic diperoxides are a very interesting series of substituted compounds in which tetroxane is the most prominent member. Gas-phase thermolysis of the simplest substituted member of the series [3-methyl-1,2,4,5-tetroxane or methylformaldehyde diperoxide (MFDP)] has been observed to yield one acetaldehyde, one formaldehyde, and one oxygen molecule as reaction products. DFT at the 6-311 + G** level of theory using the BHANDHLYP correlation-exchange functional was applied via the Gaussian09 program to calculate the critical points of the potential energy surface (PES) of this reaction. Equatorial and axial isomers were studied. The singlet state PES of MFDP was calculated, and an open diradical structure was found to be the first intermediate in a stepwise reaction. Two PESs were subsequently obtained: singlet state (S) and triplet state (T) PESs. After that, two alternative stepwise reactions were found to be possible: 1) one in which either an acetaldehyde, or 2) formaldehyde molecule is initially formed. For second one, exothermic reactions were observed for both the S and T PESs. The reaction products include a oxygen molecule in either S or T state, with the T reaction being the most exothermic. When calculations were performed at the CASSCF(10,10)/6-311 + G** level, spin-orbit coupling permitted S to T crossing at the open diradical intermediate stage, a non-adiabatic reaction was observed, and lower activation energies and higher exothermicity were generally seen for the T PES than for the S PES. These results were compared with the corresponding results for tetroxane. The spin-orbit coupling of MFDP and tetroxane yielded identical values, so it appears that the methyl substituent does not have any effect on this coupling.
The ability of herbicides to be adsorbed by the soil and their tendency to be desorbed are some of the most important factors affecting soil and water contamination. Therefore, a sorption and desorption study were conducted to evaluate the adsorption‐desorption of cyhalofop‐butyl, in the sandy clay loam and at different depths using a batch equilibrium method. The adsorption of cyhalofop‐butyl was found positively related with the clay and organic carbon content. The kinetic profiles occurred in three steps. With an initial rapid adsorption in the early hours followed by slow adsorption and then it was constant during the rest of the range studied. Adsorption data conformed well to the Freundlich isotherm, whit increasing of adsorption with increasing of organic matter of the soil of different depth. The desorption process showed an important hysteresis phenomenon. The adsorption isotherm suggested a relatively higher affinity of cyhalofop‐butyl to the adsorption sites at low equilibrium concentrations. The low value of the soil organic carbon partition coefficient (Koc) of cyhalofop‐butyl in the sandy loam soil suggested its weaker adsorption in soil and thus increased its risk of mobility into water sources.
We report the results of theoretical semiempirical AM1 and PM3 molecular orbital methods on the conformational analysis of the title compound. The relative stability of different isomers and conformers are discussed on the basis of well defined electronic and steric effects, which are rather helpful in order to understand the relative stabilities
The 2,4-dichlorophenoxyacetic acid (2,4-D) is applied to and recovered from the leaf surfaces of garden bean and corn plants. This paper examines the theoretical study of the 2,4-D IR and UV spectra as well as the determination of its optimized molecular structure. Theoretical calculations are performed at the density functional theory (DFT) levels. The different structural and electronic effects determining the molecular stability of the conformers are discussed in a comparative fashion. The optimized geometry was calculated via the B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets and the FT-IR spectra was calculated by the density functional B3LYP method with the 6-311++G(d,p) basis set. The scaled theoretical wavenumbers show good agreement with the experimental values. A detailed interpretation of the infrared spectra of 2,4-D is reported.
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