Taner Atalar

A DFT study on nitrotriazines

In this study, all possible mono-, di- and tri-nitro-substituted triazine compounds have been considered as potential candidates for high-energy density materials (HEDMs) by using quantum chemical treatment. Geometric and electronic structures, thermodynamic properties and detonation performances of these nitro-substituted triazines have been systematically studied using density functional theory (DFT, B3LYP) at the level of 6-31G(d,p), 6-31+G(d,p), 6-311G(d,p), 6-311+G(d,p) and cc-pVDZ basis sets. Moreover, thermal stabilities have been evaluated from the homolytic bond dissociation energies (BDEs). Detailed molecular orbital (MO) investigation has been performed on these potential HEDMs. According to the results of the calculations, mono-, di- and tri-nitro-substituted derivatives of symmetric 1,3,5-triazine have been found to be more stable than their 1,2,3 and 1,2,4 counterparts.

A New View of Relationships of the N–N Bond Dissociation Energies of Cyclic Nitramines. Part II. Relationships with Impact Sensitivity

The values of bond dissociation energies, BDE, of the weakest N–N bonds and total energies, Etotal, of molecules have been calculated for 14 cyclic nitramines by means of the UB3LYP/6-31G* and UB3LYP/6-31 + G* // PM3 methods. The relationships found between the BDE values and logarithms of impact sensitivity of these nitramines, expressed as drop energy, Edr, are not unambiguous. Replacement of these BDE values by the BDE/Etotal ratio has not resulted in any simplification of the said relationships, but their quality improved, particularly with application of the UB3LYP/6-31 + G* // PM3 (UHF) method. The reason of ambiguity of the relationships found mainly lies in real conformation of the respective molecules and intermolecular force effects in real molecular crystals, which are included in neither of the two calculation methods.

A DFT Study on Nitro Derivatives of Pyridine

The heat of formation values of all possible nitro derivatives of pyridine have been calculated by the application of various density functional theory (DFT) methods by a proper isodesmic reaction. The heat of formation data trends in series are found to be independent of the selected DFT method, although some differences have been observed in value. Total energies and nucleus-independent chemical shift (NICS(0)) values have also been calculated in order to jugde the aromatic stabilities for the nitropyridine derivatives. Moreover, a novel topological (Türker-Gümüş, TG) index has been defined for modeling the detonation properties of the explosives.

Computational studies on nitratoethylnitramine (NENA), its tautomers and charged forms

An energetic material, nitratoethylnitramine (NENA), its tautomers and also its charged forms are considered quantum chemically, using various basis sets at the levels of ab initio and density functional theories (DFT). NENA has been found to be sensitive to negative charge development, resulting in rupture of ONO(2) bond. Also conformational and molecular dynamics (MD) studies have been performed on NENA. Various geometrical parameters, energies and infrared spectra have been obtained and discussed. Also, calculations indicate that s-cis conformation of NENA is slightly more stable than the s-trans and the tautomers of it have very comparable total energy values to NENA. On the other hand, on the basis of homolytic bond dissociation energies (BDE) for ONO(2) bond in the structures, it is clear that the presence of the tautomers in the bulk of NENA somewhat should decrease its sensitivity.

A New View of Relationships of the N–N Bond Dissociation Energies of Cyclic Nitramines. Part III. Relationship with Detonation Velocity

The values of bond dissociation energies, BDE, of the weakest N–N bonds and total energies, Etotal, of molecules have been calculated for 14 cyclic nitramines by means of the UB3LYP/6-31G* and UB3LYP/6-31+G* // PM3 methods. Ambiguous relationships were found between the logarithms of detonation velocities and BDE/Etotal ratios of these nitramines. The reason of this found ambiguity mainly lies in a real conformation of the respective molecules and intermolecular force effects in real molecular crystals, which are included in neither of the two calculation methods. However, partial relationships of this type can be used for evaluation of effectiveness of the method of designing molecular structures of energetic cyclic nitramines for obtaining products with the maximum possible performance.

A New View of Relationships of the N–N Bond Dissociation Energies of Cyclic Nitramines. Part I. Relationships with Heats of Fusion

The values of bond dissociation energies, BDE, of the weakest N–N bonds and total energies, Etotal, of molecules have been calculated for 14 cyclic nitramines by means of the UB3LYP/6-31G* and UB3LYP/6-31+G* // PM3 methods. The relationships found between the BDE values and values of heat of fusion, ΔHm,tr, of these nitramines are not unambiguous. More unambiguous and logical relationships result from comparison of the BDE/Etotal ratio and the ΔHm,tr values. The dependences found appear suitable for prediction of the ΔHm,tr values for cis-1,3,4,6-tetranitrooctahydroimidazo[4,5-d]imidazole (31.89 kJ mol−1), 4,8,10,12-tetranitro-2,6-dioxa-4,8,10,12-tetraazaisowurtzitane (41.73 kJ mol−1), and 4,6,10,12-tetranitro-2,8-dioxa-4,6,10,12-tetraazaisowurtzitane (41.67 kJ mol−1); the predicted values of ΔHm,tr are within the expected limits and can represent a stabilizing effect of crystal lattice in decomposition reactions of the studied compounds in their molecular crystals.

Computational Study on All Possible Diamino-Dinitropyrimidines and Their Mono- and Dioxide Derivatives

Diamino-dinitropyrimidines and their mono- and dioxidized products were subjected to theoretical analysis at the level of density functional theory with the application of the B3LYP/6-31G(d,p) method of theory. The electronic energies and the nucleous-independent chemical shift (NICS) data were considered in order judge the stabilities of the systems. 4,6-Diamino-2,5-dinitropyrimidine (11), 2,6-diamino-4,5-dinitropyrimidine-1-oxide (8a), and 2,4-diamino-5,6-dinitropyrimidine-1,3-dioxide (8c) were calculated to be the most stable structures among pyrimidines and mono- and dioxide derivatives, respectively. Because these compounds are potential high-energy-density materials, their detonation parameters are also reported herein, together with bond dissociation energies regarding homolytic bond dissociation of the C-NO2 bond.

A Theoretical Study on Nitrourea and its Tautomers

In the present study, nitrourea and its possible tautomers have been subjected to theoretical analysis by performing Hartree-Fock and also density functional theory (DFT) calculations. The optimized geometries, vibrational frequencies, and some thermodynamical values for the presently considered species have been obtained in their ground states.

COMPUTATIONAL STUDIES ON NOVEL ENERGETIC MATERIALS: TETRANITRO-[2,2]PARACYCLOPHANES

Computational studies on tetranitro derivatives of [2,2]paracyclophane are carried out at B3LYP/6-31G(d,p) level of theory. Optimized geometries, electronic structures and some thermodynamic properties have been obtained in their ground states. Also, detonation performances were evaluated by the Kamlet-Jacobs equations, based on the quantum-chemical calculated densities and heat of formation values. Aromaticities were investigated by performing NICS (nucleus independent chemical shift) calculations using the gauge invariant atomic orbital (GIAO) approach at the same theoretical level. The results show that these kinds of compounds possess some properties of energetic materials and if these stable tetra-nitro substituted [2,2]paracyclophanes can be synthesized, they may be potential candidates for powerful energetic materials.

POSITIONAL EFFECT OF PHENYLENE MOIETY ON A CERTAIN PERYLENE CHROMOPHORE: A SEMIEMPIRICAL TREATMENT

A benzimidazole derivative of perylenetetracarboxylic-3,4,9,10 anhydride has been considered as the base system. Then, by means of annellation (phenylene fusion) a series of nonexistent structures have been constructed. The positional effect of annellation on these systems has been analyzed theoretically by performing PM3/RHF type quantum chemical calculations. The geometries and stabilities are discussed. The theoretical electronic spectra have been produced by using ZINDO/S (CI) type calculations and discussed.