Synthesis and investigation of 3,3'-bi-(5-trifluoromethyl-1,2,4-oxadiazole) and 5,5'-bi-(2- trifluoromethyl-1,3,4-oxadiazole)

摘要

The experimental and theoretical study of the closely related compounds: 3,3'-bi-(5-trifluoromethyl-1,2,4-oxadiazole) and 5,5'-bi-(2-trifluoro-methyl-1,3,4-oxa-diazole) are reported. In this study they are used as model species to evaluate the suitability of the heterocyclic oxadiazole ring systems for energetic materials when the fluorine atoms in the exocyclic CF_3 groups are substituted successively by nitro groups. The title compounds were isolated and characterized using multinuclear (~(13)C, ~(15)N, ~(19)F) NMR spectroscopy, vibrational (1R and Raman) spectroscopy, mass spectrometry and elemental analysis. The structures in the crystalline state were determined using low-temperature single-crystal X-ray diffraction. The thermal behavior was investigated using differential scanning calorimetry. Quantum chemical calculations for the title compounds and their derivatives containing difluoronitromethyl, fluorodinitromethyl, and trinitro-methyl groups have been performed. The gas phase absolute molar enthalpies at 298.15 K and 1 atm were calculated theoretically using the modified complete basis set method (CBS-4M) with the Gaussian 09 software. Gas phase standard molar enthalpies of formation (ΔH_(f(g))) at 298.15K were computed using the atomization energy method. Standard molar enthalpies of formation (ΔH_(f(s))) were calculated using ΔH_(f(g)) and the standard molar enthalpies of sublimation (applying Trouton's rule). By using the ΔH_(f(s)) and the densities (for the title compounds determined using X-ray diffraction at 173 K and recalculated to ambient temperature; for other compounds estimated) the detonation parameters for presented compounds were calculated using the EXPLO5 V6.02 software.