Theoretical Study on the Structure and Properties of Composite Energetic Groups

doi:10.6023/A26040105

Abstract

Breaking the development bottlenecks of traditional energetic materials has become an urgent problem to be solved in recent years. In general, energetic materials are composed of energetic groups and molecular skeletons. At present, most design strategies for energetic molecules focus on the construction of novel molecular skeletons. Inspired by the unconventional complex energetic groups reported in the literature, this study focused on the design of new "composite energetic groups". A total of 72 initial structures were obtained by combining traditional energetic groups. Theoretical calculations on their molecular structures, initial thermal decomposition mechanisms were performed via density functional theory (DFT) using the Gaussian16 program. Excellent kinetic stability ensures a sufficiently high thermal decomposition temperature and favorable chemical stability, which are essential prerequisites for the practical application of energetic molecules. Identifying accurate trigger bonds and reliable decomposition mechanisms is critical for determining the initial decomposition energy barriers. Multiple potentially fractured chemical bonds and various cleavage pathways were considered, including homolysis, heterolysis, group migration, and elimination. The Kamlet-Jacobs (KJ) equation and the EXPLO5 program were adopted to calculate detonation velocity and detonation pressure. Subsequently, 39 energetic groups were screened out based on energetic performance and kinetic stability, all possessing an initial decomposition energy barrier of ≥30 kcal•mol^-1, among which 34 were unprecedented new groups. For five experimentally synthesized structures, detailed comparisons demonstrated that the calculated thermal stability results were in excellent agreement with experimental data. Furthermore, molecular design was carried out using alkane skeletons and polyamine skeletons. It is revealed that the intramolecular strain and steric hindrance dominated by alkane skeletons, as well as the hyperconjugation effect, exert a significant influence on the kinetic stability of the final energetic molecules. All these molecules exhibit a density >2.0 g•cm^-3, a detonation velocity >8000 m•s^-1, and a detonation pressure >33 GPa.

Key words: composite energetic groups, energetic materials, molecular design, theoretical study, kinetic stability

Cite this article

Lingling Ma, Lin Ling, Yuxue Li, Long Lu. Theoretical Study on the Structure and Properties of Composite Energetic Groups[J]. Acta Chimica Sinica, 2026, 84(6): 828-839.

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Fig. & Tab. 17

Figure 1. (A) New energetic groups. 1E: Trinitromethylazo; 1H: Fluoro- bis(difluoroamino)methylazo; 1J: Tri(difluoroamino)methylazo; 2A: 2-Nitroazoxy; 2E: 1-Trinitromethylazoxy; 2F: 1-Fluorodinitromethyla- zoxy; 3A: Dinitramide; 7A: Bis(difluoramino)nitromethyl. (B) Representative compounds containing composite energetic groups

Figure 2. (A) Complex energetic groups can be regarded as combinations of simple traditional energetic groups. (B) Matrices are used to construct new "composite energetic groups"

Figure 3. Previous design strategies focused on molecular skeletons, whereas the design strategy in this work centers on energetic groups

Figure 4. The Construction Matrix for new energetic groups. Structures with a green background have an activation energy barrier greater than 30 kcal•mol-1; structures with a red background have an activation energy barrier less than 30 kcal•mol-1. Structures in blue boxes have relevant theoretical studies; structures in red boxes have reported experimental synthesis. The calculation of the energy barrier of the trigger bond is detailed in the Results and Discussion section. The red letter "R" in the leftmost column denotes the substitution position for combination

Figure 5. Typical examples of structures for composite energetic groups. Bond lengths are given in angstroms (Å). Calculated on the M06‑2X/6‑311＋G(d,p) level

Compd.	Barrier	∆_fH_Solid	ρ	Q/(cal•g^-1)	D/(km•s^-1)	P/GPa	Compd.	Barrier	∆_fH_Solid	ρ	Q/(cal•g^-1)	D/(km•s^-1)	P/GPa
1H	39.2	－156.2	1.94	1516	9.053	36.8	5I	40.2	－619.9	2.30	1617	10.098	50.6
2A	33.7	107.1	1.64	1644	8.881	33.0	5'D	33.9	524.6	1.65	1571	8.412	28.6
2B	40.4	52.4	1.70	1670	9.165	34.8	5'F	32.8	－509.3	2.09	1486	9.692	44.2
2E	35.9	136.5	1.88	1472	9.134	38.0	5'H	36.5	－641.6	2.35	1556	9.776	47.9
2F	51.1	－108.6	1.80	1410	8.800	33.2	5'I	39.2	－646.8	2.34	1649	10.136	51.5
2G	37.4	76.8	1.89	1703	9.606	41.0	6D	30.7	111.7	1.74	1243	8.578	31.9
2H	47.9	－200.3	1.98	1473	9.512	41.4	6E	32.2	－90.0	2.00	1292	9.134	39.4
2J	39.1	4.0	2.07	1719	10.107	47.9	6F	34.7	－316.4	1.94	1363	9.073	37.0
3F	32.7	－208.5	1.90	1321	8.982	35.8	6G	30.0	－127.6	2.02	1496	9.638	43.0
3G	30.7	－22.0	1.97	1483	9.566	41.7	6H	33.7	－388.4	2.09	1504	9.845	45.7
3H	33.2	－267.2	2.06	1509	9.900	45.9	6I	37.6	－370.8	2.12	1604	9.895	46.5
4B	37.7	－49.5	1.91	1142	6.618	19.0	6J	30.7	－177.0	2.15	1737	10.268	50.6
4E	34.5	－26.1	1.95	1479	9.475	40.6	7A	38.8	－210.1	1.96	1495	9.762	43.3
4F	39.4	－264.7	1.95	1573	9.663	42.2	7D	32.2	151.0	1.88	1663	9.172	37.1
4G	32.1	－79.6	2.02	1677	9.964	45.9	7F	35.9	－380.6	2.09	1511	9.852	45.7
4H	43.6	－335.0	2.12	1567	9.614	43.9	7G	31.8	－183.1	2.17	1732	10.325	51.4
4J	37.7	－134.6	2.19	1775	10.133	49.7	7H	39.6	－444.7	2.01	1592	8.956	36.8
5D	35.7	543.0	1.63	1464	8.174	27.9	7I	40.1	－435.1	2.20	1612	9.932	47.9
5F	31.6	－491.2	2.03	1312	9.248	39.5	7J	33.5	－249.0	2.27	1758	10.075	50.1
5H	32.0	－626.1	2.28	1424	9.956	49.0	CL-20	35.8	466.5	2.07	1618	9.796	46.1

Table 1. Calculated results for new energetic groups with trigger bond energy barrier≥30 kcal•mol-1. Barrier: Trigger bond energy barrier (in kcal•mol-1); ΔHf: Solid-state enthalpy of formation (in kJ•mol-1, See SI); ρ: Density (g•cm-3); Q: Detonation heat; D: Detonation velocity; P: Detonation pressure

Figure 6. The initial decomposition mechanism of 1E: (1) 1E-Path-a-Hetero: Heterolytic cleavage of Bond-a; (2) 1E-Path-b-Homo: Homolytic cleavage of Bond-b; (3) 1E-Path-b-NO2-1,3-shift: 1,3-migration of the NO2 group; (4) 1E-Path-b-HONO-Elimination: HONO elimination reaction. Selected bond lengths are in angstroms (Å), calculated at the M06-2X/6-311＋G(d,p) level

Figure 7. Key structures in the reaction pathways of Figure 6. Selected bond lengths are in angstroms (Å), calculated at the M06-2X/6-311＋G(d,p) level

Figure 8. The Initial decomposition mechanism of 2E: (1) 2E-Path-a-Hetero: Heterolytic cleavage of Bond-a; (2) 2E-Path-a-Homo: Homolytic cleavage of Bond-a; (3) 2E-Path-b-NO2-1,3-shift: 1,3-migration of the NO2 group; (4) 2E-Path-b-Homo: Homolytic cleavage of Bond-b (Å), calculated at the M06-2X/6-311＋G(d,p) level

Figure 9. Key structures in the reaction pathways of Figure 8. Selected bond lengths are in angstroms (Å), calculated at the M06-2X/6-311＋G(d,p) level

Group	Compd.	Stability	Ref.	Barrier/ (kcal•mol^-1)
1E	1E-1	室温下几天内分解	[11]	20.3
1H	1H-3	“沸点81 ℃”, “remarkable thermal stability”	[13]	39.2
1J	1J-1	核磁\色谱观察到很少量样品	[13]	21.6
2A	2A-4	DSC, T_p=164 ℃	[21]	33.7
2E	BTNAF	DSC, T_p=183.6 ℃	[34]	35.9
2F	FDNAF	DSC, T_p=233.4 ℃	[38]	51.1
3A	3A-1	在熔点分解(71~72 ℃)	[39]	26.7
7A	7A-F	室温数月没有观察到分解	[40]	38.8

Table 2. Comparison between the thermal stability of experimentally synthesized compounds containing composite energetic groups and the calculated decomposition energy barriers of trigger bonds

Figure 10. Energetic molecules composed of energetic group 7A with alkane skeletons and nitramine skeletons

Compd.	K-J Function		EXPLO5
Compd.	D	P	D	P	I_sp
7A	9762	43.3	8427	38.8	280.2
7A-PETN	10225	50.4	8679	44.1	270.3
7A-TMETN	9944	46.3	8746	43.9	275.4
7A-RDX	10145	49.2	8867	45.0	268.9
7A-HMX	10364	52.2	9007	47.1	268.9
7A-TNIW	10297	50.8	9443	48.6	278.5
Cl-20	9796	46.1	9773	44.8	272.1

Table 3. Detonation velocity (D, m•s-1), detonation pressure (P, GPa), and specific impulse (Isp, s) of the novel energetic molecules

Compd.	∆_fH_Solid	ρ	a/Å	b/Å	c/Å	Barrrier
7A	－210.1	1.96	1.480	1.541	—	38.8
7A-PETN	－513.0	2.17	1.491	1.536	1.539	33.3
7A-TMETN	－497.9	2.07	1.489	1.543	1.529	38.2
7A-RDX	－199.1	2.14	1.523	1.563	1.382	27.8
7A-HMX	－261.2	2.20	1.515	1.576	1.404	28.7
7A-TNIW	288.1	2.14	1.507	1.585	1.403	29.9

Table 4. Enthalpy of formation (∆fHSolid, kJ•mol-1), density (g•cm-3), key bond lengths (Å), and trigger bond energy barriers (kcal•mol-1) of the new energetic molecules

Figure 11. Initial decomposition mechanisms of energetic molecules 7A-PETN, 7A-TMETN and 7A-RDX

Figure 12. Selected atomic distances (Å) and bond angles (in degree) of the energetic group 7A and energetic molecules 7A-PETN, 7A-TMETN; atoms marked with C is the central carbon atom.

Figure 13. Spin density distribution of transition states and molecular orbitals related to hyperconjugation of (A) 7A-a-TS and (B) 7A-DMA-a-TS

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