A Theoretical Investigation of the Ring Strain Energy, Destabilization Energy, and Heat of Formation of CL-20

Abstract

The cage compound CL-20 (a.k.a., 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, HNIW, or 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.03,11.05,9]dodecane) is a well-studied high-energy-density material (HEDM). The high positive gas- (ΔfHg°) and solid- (ΔfHs°) phase heat of formation values for CL-20 conformers have often been attributed to the strain energy of this cage compound and, by implication, to the conventional ring strain energy (CRSE) inherent in isowurtzitane which may be viewed as a “parent compound” (although not the synthetic precursor) of CL-20. ΔfHg° values and destabilization energies (DSEs), which include the contribution from CRSE, were determined by computation using a relatively new multilevel ab intio model chemistry. Compared to cubane, isowurtzitane does not have an exceptionally high CRSE. It is about the same as that of cyclopropane and cyclobutane. These investigations demonstrate that instead of the CRSE inherent in the isowurtzitane parent compound, the relatively high ΔfHg° and DSE values of CL-20 conformers must be due, primarily, to torsional strain (Pitzer strain), transannular strain (Prelog strain), and van der Waals interactions that occur due to the presence of the six >N–NO2 substituents that replace the six methylene (–CH2–) groups in the isowurtzitane parent compound. These conclusions are even more pronounced when 2,4,6,8,10,12-hexaazaisowurtzitane is viewed as the “parent compound.”

Enthalpy of formation of CL-20

“…Two sets of 298 H f Δ (g) values for 1-6 are given in Table 3. Together with cyclic nitramines, the noncyclic nitramines, nitro compounds, and two cage molecules (adamantane and urotropin) were used as the reference species in the isodesmic reactions ( Table 2, reactions [10][11][12][13][14][15][16][17][18][19]. The reactions used in Refs.…”

Acid-Catalyzed Condensation of Benzamide with Glyoxal, and Reaction Features

“…The density of nitramines increases with increasing molecular rigidity [ 11 ]. One notable example is hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0 3,11 .0 5,9 ]dodecane (hexanitrohexaazaisowurtzitane, CL-20) ( Figure 1 ), which exhibits one of the highest detonation velocities (V 0 D = 9.36 (ε) km/s) among all of the explosives, and the highest density among the known nitranmines (ρ = 2.044 g/cm 3 ) [ 12 , 13 , 14 , 15 ], as well as a positive enthalpy of formation (ΔH f = 454 kJ/mol), optimal oxygen balance (−11.0) and detonation pressure (420 kbar) [ 16 , 17 , 18 , 19 , 20 , 21 ]. CL-20 excels compared to the other high-energy explosive materials such as HMX, RDX, PETN, etc.…”

Cage Compounds as Potential Energetic Oxidizers: A Theoretical Study of a Cage Isomer of N2O3

“…This is reflected in the heats of formation for these species, which are: 1.09 kJ g À1 (ONC) [5] > 0.97 kJ g À1 (CL-20) [6] > 0.25 kJ g À1 (HMX) [7]. A recent study [8] has shown that all of the additional energy exhibited by these cage species comes directly from the strain due to the cage structure. In the case of ONC, the cubane framework is responsible for the majority of the energy, whereas in CL-20 it is the resulting or enhanced strain among the NO 2 ligands [8].…”

“…A recent study [8] has shown that all of the additional energy exhibited by these cage species comes directly from the strain due to the cage structure. In the case of ONC, the cubane framework is responsible for the majority of the energy, whereas in CL-20 it is the resulting or enhanced strain among the NO 2 ligands [8]. While there has been a significant amount of work on the use of cage structures for fuels [2-6, 8, 9], none have been investigated as potential oxidizers.…”