Experimental and theoretical study of vibrational spectra and structure of dihalogermylene and dihalostannylene complexes with 1,4-dioxane and triphenylphosphine

Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh₃ have been reported, the structures of the complexes Cl₂Ge·C₄H₈O₂ and Cl₂Ge·PPh₃ updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X₂M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh₃ are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X₂M^II particles, still persists, suggesting that the X₂M moieties preserve their specifity as carbene analogues also in the complexes.     

A shock tube and theoretical study on the pyrolysis of 1,4-dioxane

The dissociation of 1, 2 and 4% 1,4-dioxane dilute in krypton was studied in a shock tube using laser schlieren densitometry, LS, for 1550-2100 K with 56 ± 4 and 123 ± 3 Torr. Products were identified by time-of-flight mass spectrometry, TOF-MS. 1,4-dioxane was found to initially dissociate via C-O bond fission followed by nearly equal contributions from pathways involving 2,6 H-atom transfers to either the O or C atom at the scission site. The 'linear' species thus formed (ethylene glycol vinyl ether and 2-ethoxyacetaldehyde) then dissociate by central fission at rates too fast to resolve. The radicals produced in this fission break down further to generate H, CH(3) and OH, driving a chain decomposition and subsequent exothermic recombination. High-level ab initio calculations were used to develop a potential energy surface for the dissociation. These results were incorporated into an 83 reaction mechanism used to simulate the LS profiles with excellent agreement. Simulations of the TOF-MS experiments were also performed with good agreement for consumption of 1,4-dioxane. Rate coefficients for the overall initial dissociation yielded k(123Torr) = (1.58 ± 0.50) × 10(59) × T(-13.63) × exp(-43970/T) s(-1) and k(58Torr) = (3.16 ± 1.10) × 10(79) × T(-19.13) × exp(-51326/T) s(-1) for 1600 < T < 2100 K.     

Construction of 3,9-diazatetraasteranes and 3,9-diazatetracyclododecanes by photocycloaddition reaction of 1,4-dihydropyridines: Experimental and theoretical investigation

A photocycloaddition reaction of ethyl 1,4-diaryl-1,4-dihydropyridine-3-carboxylate for the construction of 3,9-diazatetraasteranes (P₁) and 3,9-diazatetracyclododecanes (P₂) is reported for the first time. The types of reaction product clearly differ with solvent, regardless of the irradiation wavelength. The difference in P₁ and P₂ lies in the second step of the intramolecular [2 + 2] photocyclization. In order to further investigate this phenomenon and gain a deeper understanding of the photochemical behavior of 1,4-dihydropyridines, DFT and TDDFT theoretical calculations are performed. The results provide a good explanation for the formation of 3,9-diazatetraasteranes and 3,9-diazatetracyclododecanes.     

Experimental study of the kinetics of reaction of chlorine atoms with tetrahydrofuran and fully deuterated tetrahydrofuran

The overall rate constants for H-abstraction (k_H) from tetrahydrofuran and D-abstraction (k_D) from fully deuterated tetrahydrofuran by chlorine atoms in the temperature range of 298-547 K were determined. In both cases, very weak negative temperature dependences of the overall rate constants were observed, described by the expressions: k_H = (1.55 ± 0.13) × 10⁻¹⁰ exp(52 ± 28/T) cm³ molecule⁻¹ s⁻¹ and k_D = (1.27 ± 0.25) × 10⁻¹⁰exp(55 ± 62/T) cm³ molecule⁻¹ s⁻¹. The experimental results show that the value of the kinetic isotope effect (k_H/k_D), amounting to 1.21 ± 0.10, is temperature independent at 298-547 K.     

Monte Carlo investigation of the hydration of 1,4-dioxane in the chair and boat conformations

Two calculations of model systems which imitate a small drop of water (100 molecules of water) surrounding a rigid stationary molecule of 1,4-dioxane in the chair and boat conformations have been carried out in accordance with the Metropolis algorithm for a canonical ensemble. The calculations have been performed for a temperature of 300 K. The results of the calculations point out significant differences in the aqueous environment of the nonelectrolyte in the two cases. The hydration of dioxane in the boat conformation is energetically more favorable. The structure of the hydration shells has been discussed in detail.Donetsk State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 88–97, March–April, 1991.     

Gas-phase oxidation of 1,4-dioxane

An experimental investigation in a conventional static apparatus of the oxidation of equimolecular mixtures 1,4-dioxane-O₂ has shown that 1,4-dioxane reacts with oxygen more readily than most hydrocarbons. Cool flames and ignitions were observed above 200°C in a pressure range up to 300 torr. The products of the slow reaction and cool flame were analyzed by gas chromatography and GC-MS; the slow reaction gives only CO, CO₂, H₂CO, H₂, C₂H₄, and H₂O. A radical chain mechanism is suggested and discussed by using an evaluation of the rate constants of the possible elementary steps by the methods of thermochemical kinetics.     

How does the extent of substitution of methane with chlorine influence the mechanism and kinetics of the reactions between chloromethanes and atomic chlorine

A theoretical investigation of the reaction mechanism and kinetics of the reaction between chloromethanes CH_4–xCl_x (x = 1–3) and chlorine atoms was performed. The height of the reaction barrier was found to decrease with the degree of substitution of chloromethanes with atomic chlorine. A direct dynamics method was employed to study the kinetic nature of these hydrogen-abstraction reactions. The sequence of calculated reaction rate coefficients is: k(CH₃Cl + Cl) < k(CH₂Cl₂ + Cl) < k(CHCl₃ + Cl).     

Thermophysical study of 1,4-dioxane with cycloalkane mixtures

Densities, refractive indices, and surface tension for the binary mixtures 1,4-dioxane with cyclopentane or cylohexane have been determined at ambient pressure and at T = (283.15, 298.15, and 313.15) K. Excess volumes and refractive index and surface tension deviations have been calculated from the experimental data. Several relations between the thermophysical properties studied here have been tested using our experimental results.     

Thermodynamic and kinetic studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine,and 1,4-dithiine: a theoretical investigation

Theoretical studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine, and 1,4-dithiine in the gas phase were carried out using DFT methods at the B3LYP/6–311?+?G(d,p) levels of theory. The barrier height (ΔE^?) and thermodynamic parameters (ΔG^? and ΔH^?) were estimated. The progress of the reactions was followed by means of the Wiberg bond indices. The synchronicity values of the reactions were calculated. The kinetic parameters were calculated for both reactions in 300–1200-K temperature range. Also, fitted equations to the gas phase Arrhenius equation were determined. Effect of the character and number of heteroatoms were illustrated on the thermodynamic and kinetic parameters.

     

Kinetics, mechanism, and thermochemistry of the gas-phase reaction of atomic chlorine with pyridine

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of atomic chlorine with pyridine (C(5)H(5)N) as a function of temperature (215-435 K) and pressure (25-250 Torr) in nitrogen bath gas. At T> or = 299 K, measured rate coefficients are pressure independent and a significant H/D kinetic isotope effect is observed, suggesting that hydrogen abstraction is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 299-435 K for C(5)H(5)N: k(1a) = (2.08 +/- 0.47) x 10(-11) exp[-(1410 +/- 80)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2sigma, precision only). At 216 K < or =T< or = 270 K, measured rate coefficients are pressure dependent and are much faster than computed from the above Arrhenius expression for the H-abstraction pathway, suggesting that the dominant reaction pathway at low temperature is formation of a stable adduct. Over the ranges of temperature, pressure, and pyridine concentration investigated, the adduct undergoes dissociation on the time scale of our experiments (10(-5)-10(-2) s) and establishes an equilibrium with Cl and pyridine. Equilibrium constants for adduct formation and dissociation are determined from the forward and reverse rate coefficients. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the addition reaction: Delta(r)H = -47.2 +/- 2.8 kJ mol(-1), Delta(r)H = -46.7 +/- 3.2 kJ mol(-1), and Delta(r)S = -98.7 +/- 6.5 J mol(-1) K(-1). The enthalpy changes derived from our data are in good agreement with ab initio calculations reported in the literature (which suggest that the adduct structure is planar and involves formation of an N-Cl sigma-bond). In conjunction with the well-known heats of formation of atomic chlorine and pyridine, the above Delta(r)H values lead to the following heats of formation for C(5)H(5)N-Cl at 298 K and 0 K: Delta(f)H = 216.0 +/- 4.1 kJ mol(-1), Delta(f)H = 233.4 +/- 4.6 kJ mol(-1). Addition of Cl to pyridine could be an important atmospheric loss process for pyridine if the C(5)H(5)N-Cl product is chemically degraded by processes that do not regenerate pyridine with high yield.     

On the radiation-induced polyaddition of bisperfluoroisopropenyl terephthalate with 1,4-dioxane

Radical polyaddition of bis(α-trifluoromethyl-β,β-difluorovinyl)terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with 1,4-dioxane (DOX) afforded higher molecular weight polymers under γ-rays radiation from a source when compared to those yielded by benzoyl peroxide initiation. More detailed study on the radiation-induced polyaddition of BFP with DOX and optimization of the reaction conditions were carried out. It was necessary to irradiate with doses of 2000, 1500, and 750 kGy, to obtain quantitative conversion of BFP at the feed molar ratios DOX/BFP of 8.0, 16, and 32, respectively. Step-growth polymerization mechanism was suggested by the measurements of molecular weights of the polymers obtained with several irradiation doses. It was concluded that the molecular weight of the polymer could be controlled by the feed molar ratio of DOX/BFP and irradiation doses. The steep increase of molecular weight was observed at the feed molar ratio of DOX/BFP of 8.0 with the irradiation doses above 2000 kGy and the polymer with the weight-average molecular weight of 2.36×10⁴ was obtained with the dose of 3000 kGy. The reaction between polymers might take place after the quantitative conversion of BFP. Radiation-induced radical polyaddition mechanism of BFP with DOX was proposed.     

Nitration of phenol in 1,4-dioxane

The nitration of phenol with excess nitric acid in aqueous dioxane, in contrast to the nitration in aqueous ethanol, yields exclusively 2,4-dintrophenol, whereas at equimolar ratio of phenol and nitric acid the major reaction products are mononitrophenols (99%), among which the p-isomer prevails.     

Homolytic amination of benzo-1,4-dioxane

When 5,6-benzo-1,4-dioxane was reacted with N,N-dialkylchloramines in the presence of FeSO₄ at 10–20C in a solution of acetic and sulfuric acids, 6-(N,N-dialkylamino)benzo-1,4-dioxanes and 6-chloro- and 6,7-dichloro-benzo-1,4-dioxanes were obtained. Under the conditions used in the study mainly chlorination products were synthesized. Reaction of 5,6-benzo-1,4-dipxane with the system (NH₃OH)₂SO₄-TiCl₃ resulted in the formation of 6-aminobenzo-1,4-dioxane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 316–318, March, 1989.     

Experimental and theoretical studies of the phenyl radical reaction with propene

The kinetics for the reaction of C6H5 with propene has been measured by cavity ring-down spectrometry (CRDS) at temperatures 296-496 K under an Ar pressure of 40 Torr. The total rate constant can be given by the following Arrhenius expression (in units of cm3 mol(-1) s(-1)): k(C6H5 + C3H6) = 10(11.93+/-0.06) exp[-(1512 +/- 51)/T]. Density functional and higher level of theory calculations (up to the G2M level) have been carried out to provide additional insights about the mechanism of this reaction, and we also performed transition state theory (TST) calculation for the rate constant prediction. Our theoretical kinetic calculations predict that the C6H5 addition to the terminal =CH2 site in propene is dominant at the temperature range of our CRDS measurements. However, the H-abstraction channel forming benzene and the allyl radical becomes increasingly important at higher temperatures. The total high-pressure limiting rate constant calculated on the basis of the G2M reaction barriers is in reasonable agreement with the experimental values.     

Theoretical investigation of the isomers photolysis reaction for chlorine nitrate

For the reactant ClONO₂ the equilibrium geometry and energy have been calculated by using various density functional (DFT) theory methods. The harmonic vibrational frequencies were computed using the B3LYP method for the ground state of the reactant; the results were in good agreement with those of the experiment. It was shown that the DFT methods were superior to other ab initio methods in optimizing geometry and predicting vibrational frequencies. In the process of forming the products from the dissociation reactions of ClONO₂, the results indicated it undergoes the TS₂, but not the TS₁ transition state. According to the relative energies of various species, the potential energy surface reflected intuitively the mechanisms of these dissociation reactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 44–50, 2003     

1,4-二氧六环的光电离解离

采用同步辐射光源、飞行时间质谱和分子束方法研究了1．4-二氧六环的光电离解离过程．由光电离效率曲线得出离子产物的出现势，计算了产物的生成焓．若重分析了m／e=28,29.41等离子碎片的解离通道以及离子碎片的可能结构，提出1、4-二氧六环在光电离解离过程中发生了重排反应