T. S. Pivina

Computer-aided search for high-density energetic compounds among hydrogen-free heterocycles

Abstract Our general strategy of a computer-aided search for compounds with the desired physicochemical properties includes three principal stages. The first stage is the selection of possible compositions (molecular formulas) and formulation of structural requirements that may ensure the necessary properties of target compounds. The second stage is computer generation of all molecules that conform to the set of structural constraints formulated at the first stage. The third stage includes the estimation of properties for the resultant compounds and selection of the most promising structures, which may be the targets of a subsequent synthetic search. This strategy was successfully applied to search for high-density energetic compounds among nitrogen-containing hydrogen-free aromatic heterocycles structurally similar to the highly stable energetic compound known as TACOT. A number of hypothetical substances with calculated energy content and density higher than those of TACOT were predicted, and certain qualitative structure–property relationships (which may assist in a further search for compounds with similar properties within other classes) were revealed among them. Some of the predicted compounds may be proposed for synthesis, experimental study and possibly for practical use.

Methods for calculating the enthalpies of sublimation of organic molecular crystals

Four methods for calculating the enthalpies of sublimation of organic molecular crystals based on different methodological approaches are proposed. Comparative analysis of these methods was carried out and their good predictive ability with respect to various classes of compounds (aliphatic nitro compounds, acyclic and cyclic amines, amides and amino acids, benzene derivatives, heterocyclic compounds,etc.) was demonstrated.

Computer representation and generation of possible pathways for thermal decomposition reactions of organic compounds

Abstract A novel type of reaction network is proposed. During the generation of a recombination reaction network, all the starting compounds, as well as all the intermediates are considered as probable participants of transformations at every stage. This allows a more correct description of the complicated processes inherent for both radical and ionic reactions. The new networks were generated using the program complex casb . Computer modelling of a homolytic thermolysis of nitromethane, including the design of a knowledge base for the generation and evaluation of reaction enthalpies by the PM3 method, is discussed. High predictive capability of the model was observed.

Comprehensive assessment of physicochemical properties of new energetic materials

The review presents original methodological approaches and summarizes the results of research into the assessment of relationships between the structure of energetic organic compounds and their main physicochemical properties. A large number of experimental values of these parameters were statistically analyzed, and a database of the properties of explosives and rocket propellant ingredients was created. Based on the analysis and integration of these data, approaches were developed to evaluate the fundamental properties of energetic compounds of different chemical classes, such as the enthalpy of formation, the molecular crystal density, and the sensitivity to mechanical impacts. The explosive and ballistic characteristics were calculated. The comprehensive assessment was made of the possible applications of new substances and those poorly characterized by experimental methods.

Computer simulation of thermal decomposition reactions of alkyl nitrates

An approach to the construction of models for thermal decomposition of organic compounds based onrecombination reaction networks was developed. Each species (molecule, ion, or radical) is considered as a potential reagent. It was suggested that the newly formed species can react with all other species which are already present in the reaction mixture. The results of reactions are represented as a bipartite graph whose vertices are formed either by species generated or by the descriptions of interactions, while the oriented edges determine the relations between the reagents and the reaction products. Based on analysis of the experimental data on the mechanisms of thermal decomposition, empirical rules were developed for simulating possible thermal decomposition reactions of the major classes of energetic compounds. The proposed approach allows one to describe the complete spectrum of reactions occurring in the course of thermal decomposition. The approach was realized in the CASB computer program and was exemplified by simulation of thermal decomposition of methyl, ethyl, and isopropyl nitrates. All stages of the mechanisms (some of which have been reported in the literature) were reproduced. A number of new decomposition reactions, which have not been studied experimentally, are suggested.

Generation and metathesis of azomethine imines in reaction of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with het(aryl)methylidenemalononitriles

A new metathesis reaction of azomethine imines is found. Catalytic or thermal diaziridine ring opening of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes leads to azomethine imines reacting further with het(aryl)methylidenemalononitriles to give in situ new azomethine imines inaccessible by common synthetic methods. New azomethine imines are detected as pyrazolines formed via a 1,4-H shift and trapped by the [3+2] cycloaddition with various dipolarophiles to yield 1,5-diazabicyclo[3.3.0]octane derivatives bearing pharmacophoric heterocycles, e.g. furan, nitrofuran, thiophene, and indole. The best results are achieved in the Et2O·BF3-catalyzed reactions in ionic liquids.

Quantum-chemical study of the reactivity of di- and trinitropyrazoles

Quantum chemistry methods (DFT B3LYP/6-31G* (3-21G)) were used to calculate the three-dimensional and electronic structure of 4-chloro-3,5-dinitro- and 3,4,5-trinitropyrazoles, as well as their model σ-complexes. Possible reasons for the peculiar reactivity of 3,4,5-trinitropyrazole, 4-chloro-3,5-dinitropyrazole, and their derivatives were examined.

Synthesis of imidazo[4,5- e ]benzo[1,2- c ;3,4- c ´]difuroxanes

A method for the synthesis of imidazo[4,5-e]benzo[1,2-c;3,4-c´]difuroxanes, potential nitric oxide donors, has been developed. The synthesized compounds were characterized by IR and NMR spectroscopy, high resolution mass spectrometry, and elemental analysis.

QSPR approach to the calculation of rate constants of homolysis of nitro compounds in different states of aggregation

A method for theoretical estimation and prediction of rate constants of homolysis of C-N and N-N bonds is used for nitro compounds in the liquid phase. The method is based on the QSPR approach.

QSPR approach to the calculation of rate constants of homolysis of nitro compounds in different states of aggregation .2. The liquid phase

A method for the theoretical estimation and prediction of rate constants of homolysis of nitro compounds of different chemical classes in the gas phase is proposed on the basis of the QSPR approach.