Nov 9, 2017 - School of Chemical Engineering and Materials Science, Nanjing Polytechnic Institute, Nanjing 210048, China. â¡. Institute for Computati...
Theoretical Design on a Series of Novel Bicyclic and Cage Nitramines as High Energy Density Compounds ... Publication Date (Web): November 9, 2017 ... The results indicate that our unusual design strategy that constructing bicyclic or cage nitramines
Nov 9, 2017 - In particular, five compounds exhibit a best combination of better oxygen balance, good thermal stability, excellent detonation properties superior to or comparable to CL-20 or HNHAA, and lower impact sensitivity than CL-20 or HNHAA. Th
Nov 9, 2017 - (51) Generally, the higher h50 is, the more sensitive is the explosive. Table 5 lists the estimated impact sensitivity (h50) of the title compounds. For comparison, the predicted h50 values of HMX, CL-20, and HNHAA are given. The calcul
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May 31, 2012 - resulted in the identification of benzimidazole 44a as a GSM with low nanomolar potency in vitro. In mouse, rat, and dog, this compound ...
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Article
Theoretical Design on a Series of Novel Bicyclic and Cage Nitramines as High Energy Density Compounds Yong Pan, and Weihua Zhu J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b10462 • Publication Date (Web): 09 Nov 2017 Downloaded from http://pubs.acs.org on November 13, 2017
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Theoretical Design on a Series of Novel Bicyclic and Cage Nitramines as High Energy Density Compounds Yong Pan †, ‡, Weihua Zhu*, ‡ †
School of Chemical Engineering and Materials Science, Nanjing Polytechnic Institute, Nanjing 210048, China ‡ Institute for Computation in Molecular and Materials Science and Department of Chemistry, Nanjing University of Science and Technology, Nanjing 210094, China
ABSTRACT: We designed four bicyclic nitramines and three cage nitramines by incorporating -N(NO2)-CH2-N(NO2)-, -N(NO2)-, and -O- linkages based on the HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) framework. Then, their electronic structure, heats of formation, energetic properties, strain energy, thermal stability, and impact sensitivity were systematically studied using DFT. Compared to the parent compound HMX, all the title compounds have much higher density, better detonation properties, and better oxygen balance. Among them, four compounds have extraordinary high detonation properties (D > 9.70 km/s and P > 44.30 GPa). Moreover, most of the title compounds exhibit better thermal stability and lower impact sensitivity than CL-20 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) or HNHAA. Thus, all of the seven new nitramine compounds are promising candidates for high energy density compounds. In particular, five compounds exhibit a best combination of better oxygen balance, good thermal stability, excellent detonation properties superior to or comparable to CL-20 or HNHAA, and lower impact sensitivity than CL-20 or HNHAA (hexanitrohexaazaadamantane). The results indicate that our unusual design strategy that constructing bicyclic or cage nitramines based on the HMX framework by incorporating the intramolecular linkages is very useful for developing novel energetic compounds with excellent detonation performance and low sensitivity.
1. INTRODUCTION In recent years, substantial efforts have been devoting to designing and developing novel high energy density compounds (HEDCs) to meet continuing requirements for improved energetic materials.1-4 The ideal HEDC requires excellent energetic performance, good thermal stability, and low sensitivity to outer stimuli. Unfortunately, the requirements of high detonation performance and insensitivity are often contradictory each other. Therefore, many studies are desired to obtain new HEDCs possessing a good balance between the detonation performance and sensitivity.5 As an important class of promising candidates for HEDCs, cyclic nitramines have been attracting considerable attention due to their favorable energetic performance, good thermal stability, and low impact sensitivity.5-13 For example, HMX (1,3,5,7tetranitro-1,3,5,7-tetrazocane) and RDX (1,3,5-trinitro-1,3,5-triazinane), two wellknown explosives, have been extensively used for military and civilian applications for a long time. In particular, HMX exhibits a good balance between the sensitivity and explosive performances, with relatively low impact sensitivity (h50=29 cm) 14 and high energetic performances (density 1.9 g/cm3, detonation velocity 9.10 km/s, detonation pressure 39.0 GPa), which are very close to the criteria of the HEDMs (density >1.9 g/cm3, detonation velocity >9.0 km/s, detonation pressure >40.0 GPa). 15,16
Accordingly, the framework of HMX can be regarded to be a good parent
structure for developing novel HEDCs. It had been found that it was a popular and effective strategy to obtain better energetic performances by incorporating more nitro groups via C- or N-functionalization based on the HMX framework, and many new cyclic nitramines have been successfully developed as candidates for HEDCs. However, these derivatives can generally gain satisfying energetic performance when
seven or more nitro groups were introduced into the cyclic nitramines, which also makes them very sensitivity to outer stimuli and difficult to handle safely in experimental study and industrial production. In addition, energetic compounds containing seven or more nitro groups are very difficult to be synthesized. Thus, further research is required to look for a new method to tailor the structure of HMX to gain novel HEDCs with improved energetic properties and low sensitivity. Generally, compared to the monocyclic nitramines, polycyclic or cage nitramines compounds
such
as
CL-20
(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-
hexaazaisowurtzitane) and HNHAA (hexanitrohexaazaadamantane, see Scheme 1) have a more compact structure with a large ring or cage strain.4,16,17 Hence, it ultimately leads to the polycyclic or cage nitramines having higher density, higher energy, and higher detonation performances than monocyclic nitramines. Therefore, constructing polycyclic or cage structure based on the framework of HMX may give rise to remarkable increase in heat of formation, density, and detonation performance. On the other hand, for HMX, the relatively low oxygen balance (OB = -21.62%) restrict the energy release due to incomplete redox reaction. Naturally, it is also essential to introduce nitro groups into the new designed compounds to improve the oxygen balance. < Scheme 1 about here> In this work, seven novel bicyclic or cage nitramines (Scheme 2) were designed based on the new strategy. Firstly, energetic groups such as -N(NO2)-CH2-N(NO2)and -N(NO2)- were chosen as intramolecular linkages rather than substituents. Also, the -O- linkage is introduced to avoid excessive nitro groups in the molecule to improve the oxygen balance. Moreover, four novel bicyclic nitramines, R1, R2, R3 and R4, were formed by linking the C2 and C6 (or C4) in the HMX structure using -
N(NO2)-CH2-N(NO2)-, -N(NO2)-, and -O- linkages, respectively. Finally, three novel cage nitramines were generated by properly introducing -N(NO2)-, -O-, and - linkages to link the C atoms in the molecular structure of bicyclic nitramines. Then, the electronic structure, HOFs, energetic properties, strain energy, thermal stability, and impact sensitivity for the title compounds were investigated by using density functional theory (DFT). Our main purpose is to screen novel energetic cage compounds with high energy and low sensitivity. < Scheme 2 about here> 2. COMPUTATIONAL METHODS The hybrid DFT-B3LYP methods with the 6-311G(d,p) basis set were adopted for the optimizations of the molecular structures and the predictions of HOFs. Previous studies have shown that the basis set 6-311G(d,p) is able to precisely predict the molecular structures and energies of energetic organic compounds.6,18-20 The gas-phase HOFs were estimated based on the isodesmic reactions, in which the numbers of all kinds of bonds can keep invariable is widely used to decrease the calculation errors of HOFs.20-23 To obtain a more accurate calculation results, the basic ring skeleton of the parent compound is kept invariable in the designed isodesmic reactions. The corresponding isodesmic reactions used to obtain the gasphase HOFs of the title compounds are as follows: NO2 N
NO2 N NO2 N NO2 + 3 CH + 4 NH N 4 3 N N NO2 O2N O NO2 N N NO2 + 2 CH4 N N NO2 O2N HMX + 4 CH3CH2CH3 + 4 NH3
For the isodesmic reaction, the heat of reaction ∆H298K at 298 K can be calculated from the following equation:
∆H 298 K = ∑ ∆H f , P −∑ ∆H f , R
(4)
where ∆Hf,R and ∆Hf,P are the HOFs of reactants and products at 298 K, respectively. At the same time, the ∆H298K can be calculated using the following expression:
∆H 298 K = ∆E298 K + ∆( PV ) = ∆E0 + ∆ZPE + ∆HT + ∆nRT
(5)
where ∆E0 is the change in total energy between the products and the reactants at 0 K; ∆ZPE is the difference between the zero-point energies (ZPE) of the products and the reactants at 0 K; ∆HT is thermal correction from 0 to 298 K. The ∆(PV) value in eq. (5) is the PV work term and equals ∆nRT for the reactions of ideal gas. Since most energetic compounds are usually solid, the calculation of detonation properties requires solid-phase HOF (∆Hf,solid).24 According to Hess’s law of constant heat summation,25 the gas-phase HOF (∆Hf,gas) and heat of sublimation (∆Hsub) are used to evaluate ∆Hf,solid:
∆H f ,solid = ∆H f , gas - ∆H sub
(6)
The ∆Hsub can be calculated by the empirical expression suggested by Politzer et al.:24,26
∆H sub = aA2 + b(νσ tot2 )0.5 + c
(7)
where A is the surface area of the 0.001 electrons/bohr3 isosurface of electronic density of the molecule, ν describes the degree of balance between positive and 2 negative potential on the isosurface, and σ tot is a measure of variability of the
electrostatic potential on the molecular surface. The coefficients a, b, and c were determined by Rice et al: a = 2.670×10-4 kcal/mol/Å4, b = 1.650 kcal/mol, and c 2 =2.966 kcal/mol.27 The descriptors A, ν, and σ tot were calculated using the
computational procedures proposed by Bulat et al..28 This approach has been used to credibly evaluate heats of sublimation of many energetic compounds.27,29,30 The detonation velocity and pressure were estimated by the Kamlet-Jacobs equations 31 as D = 1.01(N M
1/2
P = 1.558ρ2N M
Q1/2)1/2 (1 + 1.30ρ) 1/2
(8)
Q1/2
(9)
where each term is defined as follows: D, the detonation velocity (km/s); P, the detonation pressure (GPa); N, the moles of detonation gases per gram explosive; M , the average molecular weight of these gases; Q, the heat of detonation (cal/g), which can be evaluated by the HOF difference between products and explosives according to the principle of exothermic reactions; and ρ, the crystal density of explosives (g/cm3). The crystal density was obtained based on an improved approach proposed by 2 Politzer et al.,32 in which the interaction index νσ tot was introducd.
M 2 + β 2 (νσ tot ) + β 3 V (0.001)
(10)
ρ = β1
in which M is the molecular mass (g/mol), and V(0.001) is the volume of the 0.001 electrons/bohr3electronic density of the molecule (cm3/molecule). The coefficients β1, β2, and β3 are 1.0462, 0.0021, and -0.1586, respectively.33 Strain energy (SE) is an important parameter for assessing the stability and reactivity of organic polycyclic or cage compounds. Here, strain energies of the title compounds were investigated via the method of homodesmotic reaction, which can successfully predict strain energy from the change of total energies (E0) with zeropoint energies (ZPE):34-37
The strength of bonding, which could be evaluated by bond dissociation energy (BDE), is fundamental to understand chemical processes.38 The energy required for bond homolysis at 298 K and 1 atm corresponds to the enthalpy of reaction A-B(g) → A·(g) + B·(g), which is the bond dissociation enthalpy of the molecule A-B by definition.39 For many organic molecules, the terms “bond dissociation energy” (BDE) and “bond dissociation enthalpy” often appear interchangeably in the literature.40 Therefore, at 0 K, the homolytic bond dissociation energy can be given in terms of eq. (13). BDE0(A-B) → E0(A·) + E0(B·) – E0(A-B)
(12)
The bond dissociation energy with zero-point energy (ZPE) correction can be calculated by eq. (13). BDE(A-B)ZPE = BDE0(A-B) + ∆EZPE
(13)
where ∆EZPE is the difference between the ZPEs of the products and the reactants. The impact sensitivity (h50, cm) can be predicted by the equation proposed by Pospíšil et al.:14,41 h50 = ασ +2 + βν + γ
(14)
where h50 is measured by a 2.5 kg dropping mass upon a sample to determining the height from which there is a 50% probability of causing an explosion,42,43 σ +2 is the indicator the strengths and variabilities of the positive surface potentials, and ν is the balance of charges between positive potential and negative potential on the molecular surface. The coefficients α，β，and γ are -0.0064, 241.42, and -3.43, respectively. The calculations were performed with the Gaussian 09 package.44 The optimizations were performed without any symmetry restrictions using the default convergence criteria in the program. All of the optimized structures were characterized to be true local energy minima on the potential energy surfaces without
imaginary frequencies. 3. RESULT AND DISCUSSION 3.1. Molecular Geometry and Electronic Structure. The optimized structures of the title compounds are displayed in Figure 1. The 3D plots of highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and their energy gaps (∆E) of the seven energetic compounds were illustrated in Figure 2, in which the positive phase is shown in red, while the negative one is shown in green. Obviously, most of the HOMO and LUMO levels are 2-fold degenerate, which shows that the removal of an electron from the HOMO level or addition of an electron to the LUMO level could weaken the bicyclic or cage skeleton. The energy gap is an important parameter which can evaluate the reactivity in the chemical or photochemical processes with electron transfer or leap. Seen from Figure 2, all of the title compounds have relatively large energy gaps from 5.33 to 6.15 eV, which shows that these molecules exhibit good stabilities in the chemical process. Among them, R3 has the largest energy gap (∆E), whereas R4 has the smallest energy gap (∆E). Electrostatic potentials can be used to analyzing the impact sensitivity of energetic compounds. Previous studies indicated that the molecules that are more sensitive have significant electron deficiencies (positive potentials) within the molecule.45 Figure 3 illustrated molecular electrostatic potentials (MEPs) of the title compounds for the 0.001 electron/bohr3 isosurface of electron density that were evaluated at the B3LYP/6-311G(d, p) level. The colors range from -0.03 to 0.05 Hartree, with red denoting the most negative potential and blue denoting the most positive potential.
Seen from the MEPs of the title compounds, the positive potentials ranges at the center of the ring or cage skeleton, while the negative potentials appear to be mostly distributed on the N-NO2 moiety. Clearly, R1, R4, R5, and R6 have stronger positive potential focused in the inner region than other three compounds, which might result in relatively high impact sensitivity. < Figure 3 about here> 3.2. Gas-phase and Solid-phase Heats of Formation. The solid-phase HOF (∆Hf,solid) is an important property for energetic materials. Table 1 lists the total energies, ZPEs, thermal corrections and HOFs for reference compounds in the isodesmic reactions. The gas-phase HOFs of CH4, NH3, CH3NH2, CH3CH3, CH3NHCH3, CH3OCH3, CH3CH2CH3, and cyclooctane were taken from experimental results.46,47 The ∆Hf,gas of NH2NO2 was calculated from the atomization reaction at the G3 level.
Table 2 presents the total energies, ZPEs, thermal corrections, ∆Hf,gas, and ∆Hf,solid of the title compounds. The calculated ∆Hf,gas value of HMX is in agreement with previous reports,6,48,49 indicating that our predicted results is to be credible. Obviously, all of the title compounds exhibit high positive gas-phase and solid-phase HOFs. R4 has the highest ∆Hf,gas (804.01 kJ/mol) and ∆Hf,solid (654.86 kJ/mol) among these compounds. In particular, except for R3, the title compounds have much larger ∆Hf,gas and ∆Hf,solid values than the parent compound HMX. It shows that constructing a bicyclic or cage skeleton based on a monocyclic framework by incorporating energetic groups can remarkably increase the HOFs of the parent compound. The reason for that is mainly because the strain inherent in the bicyclic or cage system can release additional energy to result in large positive HOFs.4,50
3.3 Detonation Properties. Detonation velocity (D) and detonation pressure (P) are two important performance parameters for energetic materials. The calculated ρ, Q, D, P, and oxygen balance (OB) of the title compounds were presented in Table 3. For the purpose of comparison, the calculated energetic properties of HNHAA and HMX are given. The semi-empirical Kamlet-Jacobs formula has been proved to be reliable for predicting the explosive properties of energetic high-nitrogen compounds.12,21 The calculated ρ, D, and P of HMX are consistent with the experimental values and previous calculated values,4,6 indicating that our calculated results for the title compounds are very reliable.
Generally, the higher the oxygen balance is, the larger the detonation velocity and pressure are. However, too much oxygen is not favorable for improving explosive performance of energetic compounds, as the additional oxygen will produce O2 that takes away a great deal of energy during the explosion of energetic materials. Thus, the ideal oxygen balance is equal to zero. As shown in Table 4, the OB values (ranging from -10.32% to 3.29% ) of the title compounds are very close to zero, exhibiting a better oxygen balance compared to that of HMX (-21.62%). Especially, the oxygen balance of R7 is equal to zero, making it combust completely and so avoid releasing some toxic gases such as carbon monoxide in its decomposition. In addition, all of the title compounds possess higher heat of detonation (Q) compared to their parent compound HMX except for R3. Among them, R4 has an outstandingly high Q value (1784.42 cal/g). Figure 4 displays a comparison of the ρ, D, and P of the title compounds, HMX, CL-20, and HNHAA. As shown in Table 3 and Figure 4, all of the title compounds
exhibit surprisingly high density ranging from 1.91 to 2.03 g/cm3, which are higher than that of HMX. The densities of R5, R6, and R7 are comparable with that of CL-20 or HNHAA. Moreover, all of the title compounds have obviously higher density, better oxygen balance, and higher heat of detonation than HMX. Especially, R4, R5, R6, and R7 present extraordinary high detonation properties (D > 9.70 km/s and P > 44.30 GPa), superior to those of CL-20 (9.40 km/s and 42.00 GPa)15,24 and HNHAA (9.64 km/s and 44.10 GPa). In addition, even if R3 has a much lower HOF value than HMX, it possesses a remarkably high detonation performances superior to HMX, owing to its bicycle skeleton in the molecule to a great degree. Overall, all of the title compound exhibit high density and excellent detonation performances, which are obviously higher than those of HMX and comparable with those of CL-20 or HNHAA. The predicted results further confirm that constructing bicyclic or cage nitramine compounds based on the framework of HMX is an effective way to remarkably enhance the energetic properties. 3.4 Strain Energies. The calculated strain energies of the title compounds and HMX are given in Table 4. It is found that all of the title compounds have higher strain energy than HMX, and the bicyclic compound R4 have the highest strain energy among them. It may be inferred that the bicyclic or cage compounds have a larger strain than its monocyclic analogues. In addition, it is found that these compounds having relatively large strain energy often exhibit a higher HOF, as the high strain energy in the structure system can be released in explosion and so increase the energy for these energetic compounds. In addition, although R2 and R3 have similar bicyclic skeleton, the strain energy of R3 is lower than that of R2 (about 56 kJ/mol). A similar situation can also be found
between R5 and R7. Therefore, it may indicate that R3 or R7 has better thermal stability than R2 or R5, respectively. That is to say, the stability of energetic compounds can be improved when the N-NO2 group in the cyclic or cage nitramines is replaced by the oxygen atom. < Table 4 about here> 3.5 Thermal Stability. Bond dissociation energy (BDE) can provide useful information for understanding the stability of a molecule. On the whole, the smaller the energy for breaking a bond is, the weaker the bond is, and the easier the bond becomes a trigger bond. To investigate thermal stability of the title compounds, four possible bond dissociations are considered: (1) the N-NO2 bond linked to the ring or cage; (2) the C-N bond in the ring or cage; (3) the C-O bond in the ring or cage; (4) the C-C bond in the cage only for R6. The BDEs of the relatively weaker bonds of the title compounds were also presented in Table 4. Obviously, the N-NO2 bonds of the title compounds have lower BDE values than other bonds in the molecule except for R4, indicating that the N-NO2 bonds are the weakest one and the rupture of the N-NO2 bond is likely the initial step in thermal decomposition for these compounds. The weakest C-N bond of R4 has lowest BDE value (108.77 kJ/mol) among these compounds, and its BDE of the relatively weaker N-NO2 bond is much lower than those of other compounds. It shows that R4 has a relatively low thermal stability, which attributes to the relatively large strain in its bicyclic structure. On the whole, all of the title compounds exhibit good thermal stability, as they have relatively high BDE values of the weakest bond and meet the requirement that the candidate for HEDCs should have a dissociation barrier larger than 80-120 kJ/mol. 3.6. Impact Sensitivity. Impact sensitivity (h50) is often used to judge whether
energetic compounds are sensitive or insensitive to external impact.51 Generally, the higher h50 is, the more sensitive is the explosive. Table 5 lists the estimated impact sensitivity (h50) of the title compounds. For comparison, the predicted h50 values of HMX, CL-20, and HNHAA are given. The calculated h50 value of CL-20 or HMX agrees well with the experimental data,52,53 indicating that our predicted results in the section are credible. < Table 5 about here> Seen from Table 5, though the h50 values of the title compounds is lower than the parent compound HMX, these compounds exhibit much higher h50 values than CL-20 or HNHAA except for R1. It may be concluded that R2 to R7 are anticipated to be more insensitive to external impact than HNHAA or CL-20. In addition, R3 has the highest h50 value among all the compounds, and R5 has the highest h50 value among the three cage compounds. It may show that the introduction of the oxygen atom can effectively improve the sensitivity of the bicyclic or cage compound. Generally, among these compounds, R2, R3, and R7 have relatively high h50 values and show relatively low impact sensitivity, which is consistent with the analysis on molecular electrostatic potentials as mentioned above. Therefore, it may be concluded that all of the title compounds can be regarded as potential candidates of HEDCs. In particular, R2, R4, R5, R6, and R7 exhibit excellent detonation properties superior to or comparable to CL-20 or HNHAA, and lower impact sensitivity than CL-20 or HNHAA. Hence, the five nitramines may be very attractive potential HEDCs. 4. CONCLUSIONS In this work, four bicyclic nitramines and three cage nitramines were designed based on the framework of HMX. Then, their electronic structure, HOFs, energetic
properties, strain energy, thermal stability, and impact sensitivity were systematically studied using the DFT-B3LYP method. It is found that all the title compounds have much higher density, higher detonation properties and better oxygen balance than the parent compound HMX. Especially, R4, R5, R6, and R7 present extraordinary high detonation properties (D > 9.70 km/s and P > 44.30 GPa). Moreover, except for R1 and R3, the title compounds exhibit a best combination of better oxygen balance, good thermal stability, excellent energetic properties superior to or comparable with CL-20 or HNHAA, and lower impact sensitivity than CL-20 or HNHAA. Thus, all of the seven novel nitramine compounds are promising candidates for HEDCs. In addition, our design strategy that the construction of bicyclic or cage nitramines based on the framework of HMX by incorporating the intramolecular -N(NO2)-CH2N(NO2)-, -N(NO2)-, and -O- linkages is a valuable approach to develop novel HEDCs with both excellent performance and low sensitivity.
ASSOCIATED CONTENT Supporting Information Calculated Total Energies (E0), Zero-point Energies (ZPE), Thermal Corrections (HT), and Gas HOFs for the Title Compounds at the B3PW91/6-311G(d,p) level . Cartesian XYZ Coordinates (in Å) for the Optimized Structure of the Title Compounds (R1-R7) at the B3LYP/6-311G(d,p) level.
AUTHOR INFORMATION Corresponding Author *(W.H. Zhu) E-mail address: [email protected]. Fax: +86 25 84303919. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant
No. 21273115) and was sponsored by Qing Lan Project of Jiangsu Province in China.
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Scheme 1. Molecular structure of RDX, HMX, CL-20, and HNHAA Scheme 2. Molecular frameworks of seven designed nitramines (R1-R7) Figure 1. Molecular structures of the title compounds. Figure 2. HOMO and LUMO energy levels and energy gaps of seven designed compounds. Figure 3. Electrostatic potentials mapped of the title compounds, color coding for MEPs are from red (negative) to blue (positive). Figure 4. Densities, detonation velocities and detonation pressures of the title compounds. Table 1. Calculated Total Energies (E0), Zero-point Energies (ZPE), Thermal Corrections (HT), and Gas-phase HOFs for the Reference Compoundsa Table 2. Calculated Total Energies (E0), Zero-point Energies (ZPE), Thermal Corrections (HT), Heats of Sublimation (∆Hsub), and HOFs for the Title Compoundsa Table 3. Predicted Densities (ρ), Heats of Detonation (Q), Detonation Velocities (D), Detonation Pressures (P), and Oxygen Balance (OB) for the Title Compoundsa Table 4. Strain Energies (SE, kJ/mol) via Homodesmotic Reactions, and Bond
Table 2. Calculated Total Energies (E0), Zero-point Energies (ZPE), Thermal Corrections (HT), Heats of Sublimation (∆Hsub), and HOFs for the Title Compoundsa Compd.
444.22 276.08 0.10 165.08 125.65 318.57 177.79 250.42 0.12 165.76 113.33 64.46 804.01 304.68 0.08 276.43 149.15 654.86 729.22 339.16 0.08 190.79 168.38 560.83 590.15 314.00 0.08 257.13 154.72 435.43 460.18 317.29 0.10 179.11 153.75 306.42 267.35 HMX -1196.8744 0.1909 49.57 (263.70, 123.41 143.94 272.63)b a E0 and ZPE are in a.u.; HT, ∆Hsub and HOFs are in kJ/mol; σ tot2 is in kcal/mol and A is in Å2. The scaling factor for ZPE is 0.98. b
Table 3. Predicted Densities (ρ), Heats of Detonation (Q), Detonation Velocities (D), Detonation Pressures (P), and Oxygen Balance (OB) for the Title Compoundsa
Table 4. Strain Energies (SE, kJ/mol) via Homodesmotic Reactions, and Bond Dissociation Energies (BDE, kJ/mol) of the Relatively Weak Bonds for the Title Compounds BDE of BDE of C-N N-NO2 R1 322.30 156.89 250.48 R2 280.17 148.92 237.95 R3 219.40 151.31 279.17 R4 595.43 132.66 108.77 R5 463.03 143.04 257.15 R6 345.38 145.24 285.65 R7 399.41 135.19 308.44 143.85 246.52 HNHAA (142.65a) (252.07a) a The calculated value in parentheses are from Ref. 16. Compd.
