Novel efficient synthesis of β-fluoro-β-(trifluoromethyl)styrenes

CF₃CFBr₂ was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF₃CFBr₂ under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested.     

Mechanistic study of multi-step nucleophilic substitution for trifluoromethylated styrenes

The key steps of the reactions of nitrogen nucleophiles with β-halogen-β-trifluoromethylstyrenes have been studied by ¹⁹F and ¹H NMR monitoring and quantum-chemical calculations. In contrast to the mechanism proposed earlier for nucleophilic vinylic substitution of captodative carbonyl-bearing haloalkenes, this reaction proceeds via either E–Ad or Ad–E sequence depending on the nature of aromatic substituents of the parent styrenes.     

Reaction of Diaryl Telluroxides with HBF4

Russian Journal of Organic Chemistry -     

Calculation of chemical potentials of chain molecules by the incremental gauge cell method

The gauge cell Monte Carlo method is extended to calculations of the incremental chemical potentials and free energies of linear chain molecules. The method was applied to chains of Lennard-Jones beads with stiff harmonic bonds up to 500 monomers in length. We show that the suggested method quantitatively reproduces the modified Widom particle insertion method of Kumar et al. [S. K. Kumar, I. Szleifer, and A. Z. Panagiotopoulos, Phys. Rev. Lett. 66(22), 2935 (1991)], and is by an order of magnitude more efficient for long chains in terms of the computational time required for the same accuracy of chemical potential calculations. The chain increment ansatz, which suggests that the incremental chemical potential is independent of the chain length, was tested at different temperatures. We confirmed that the ansatz holds only for coils above the θ temperature. Special attention is paid to the effects of the magnitude of adsorption potential and temperature on the behavior of single chains in confinements that are comparable in size with the free chain radius of gyration. At sufficiently low temperatures, the dependence of the incremental chemical potential on the chain length in wetting pores is superficially similar to a capillary condensation isotherm, reflecting monolayer formation following by pore volume filling, as the chain length increases. We find that the incremental gauge cell method is an accurate and efficient technique for calculations of the free energies of chain molecules in bulk systems and nanoconfinements alike. The suggested method may find practical applications, such as modeling polymer partitioning on porous substrates and dynamics of chain translocation into nanopores.     

Ab initio calculations of the electronic states of AsH2 including dissociation characteristics

Multireference configuration interaction calculations have been carried out for low-lying electronic states of AsH(2). Bending potentials for the ten lowest states of AsH(2) are obtained in C(2v) symmetry for As-H distances fixed at the the ground state equilibrium value of 2.845 a(0), as well as for the minimum energy path constrained to R(1) = R(2). The calculated equilibrium geometries for the X?(2)B(1) ground state and the A?(2)A(1) excited state agree very well with the previous experimental and theoretical results, whereas the data for the higher-lying states are obtained for the first time. Asymmetric potential energy surface (PES) cuts (at R(1) = 2.845 a(0), θ = 90.7°) and two-dimensional (2D) PESs for the lowest three states are also new. The calculated ab initio data are used for analysis of possible AsH(2) photodissociation channels and predissociation effects. It is shown that the A?(2)A(1)-X?(2)B(1) transition dipole moment decreases with increasing bending angle, which influences the intensity distribution in the A?(0,0,0)→X? emission spectrum (v(2)' bending series), shifting its maximum to smaller v(2)' quantum numbers.     

Polynomial approximation of nonlinear differential systems with prefixed accuracy

This paper presents a method for constructing polynomial approximations of the solutions of nonlinear initial value systems of differential equations. Given an a priori chosen accuracy, the degree of the vector polynomial can be adapted so that the approximate solution has the required precision. The method is based on the AI-method of Dzyadyk developed for the scalar case, and the computational cost is shown to be competitive with other methods.     

Cavitation and crystallization in a metastable Lennard-Jones liquid at negative pressures and low temperatures

Molecular dynamics simulations have been used to investigate the kinetics of spontaneous cavitation and crystallization in a Lennard-Jones liquid at negative pressures in the temperature range where these processes compete with each other. The nucleation rate has been calculated in NVE and NpT ensembles by the method of mean lifetime and the transition interface sampling method with parallel path swapping. The data obtained have been used to determine in the framework of classical nucleation theory the value of the ratio of the solid-liquid and the liquid-void interfacial free energy for critical crystals and cavities and the values of their volumes at points where the cavitation rate of the liquid is equal to the rate of its crystallization.     

Molecular modeling of organophosphorous agents and their aqueous solutions

Using molecular dynamics simulations, we modeled solvation and diffusion in aqueous solutions of organophosphorous compounds, including nerve G-agents sarin and soman (methylphosphonofluoridates) and their common simulants DMMP (dimethyl methylphosphonate) and DIFP (diisopropyl fluorophosphate). The aqueous solutions of the organophosphorous compounds were found to display complex molecular scale structures and dynamic properties due to competing interactions between strongly hydrophobic and hydrophilic groups. The mixing of agents with water was proved to be exothermic with negative excess mixing volume, indicating a strongly hydrophilic solvation. This effect was confirmed in a specially performed experiment. We discuss to what extent DMMP and DIFP are suitable simulants for G-agents in experimental studies, as far as their interactions with water are concerned. We also focus on the relevance of the structural features and mobilities of agents in water to their interactions with permselective polyelectrolyte membranes that may be employed as protective barriers against chemical warfare agents.