## 3 High Energy Density Materials (HEDMs)  
High energy density materials (HEDMs) are a class of compounds characterized by a high ratio of potential energy to density. They are used in various fields, including quarries, pyrotechnics, artillery weapons, and even rocket fuels [88]. The first high-energy material to be developed was nitroglycerin (**32**, Figure 5), which was discovered by [PERSON] in the late 19 th century. Glycerol trinitrate (**32**, TNG) is notable for its high nitrogen (18.5%) and oxygen (63.4%) content, making it both an oxidant and a reductant. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Entry** & \begin{tabular}{c} **Precursor** \\ **(Method)** \\ \end{tabular} & \(\mathbf{R^{1},R^{2}}\) & **Conditions** & **Yield [\%]** & **Ref.** \\ \hline \multirow{4}{*}{1} & & & C(CH3)\({}_{3}\)\({}_{3}\) 3-NO\({}_{2}\)-C\({}_{6}\)H\({}_{4}\), & & & \\  & & R = 3-F-C\({}_{6}\)H\({}_{4}\), & & & & \\  & & 3,5-bis(CF3)-C\({}_{6}\)H\({}_{3}\), & & & reflux, [Ox] & 42–75 & [39; 40] \\  & & & 2-yl, 4-CF3-C\({}_{6}\)H\({}_{4}\), & & & \\  & & 2-NO\({}_{2}\)-C\({}_{6}\)H\({}_{4}\) & & & & \\ \hline \multirow{2}{*}{2} & \begin{tabular}{c} Aldehyde (**21**) \\ (Method 2.5) \\ \end{tabular} & CH\({}_{3}\), C\({}_{2}\)H\({}_{5}\), C(CH3)\({}_{3}\) & NH\({}_{2}\)NH\({}_{2}\), O\({}_{2}\) (Pd/C), & & & \\  & & & HNO\({}_{3}\) & & [19; 68; 69] \\ \hline \multirow{3}{*}{3} & \begin{tabular}{c} Guanidine \\ hydrochloride (**22**) \\ (Method 2.6) \\ \end{tabular} & \multirow{3}{*}{3,5-dimethyllypyrazol-1-yl} & \multirow{3}{*}{2,4-pentadiene, 70 \({}^{\circ}\)C, [Ox]} & \multirow{3}{*}{95} & \multirow{3}{*}{[71; 77; 78]} \\  & & & & & \\ \hline \multirow{2}{*}{4} & \begin{tabular}{c} Thiocarbohydrazide (**26**) \\ (Method 2.7) \\ \end{tabular} & H, CH\({}_{3}\), C\({}_{6}\)H\({}_{5}\) & RC(OC\({}_{2}\)H\({}_{5}\))\({}_{3}\), NE\({}_{3}\), EtOH, & & & \\ \hline \multirow{2}{*}{5} & \
\begin{tabular}{c} Ethyl diaoacetate (**29**) \\ (Method 2.8) \\ \end{tabular} & COOCH\({}_{3}\) & NaOH, HCl, SOCI\({}_{2}\), & & \\  & & & MeOH, \(-30\) \({}^{\circ}\)C, [Ox] & & \\ \hline \multirow{2}{*}{6} &
\begin{tabular}{c} Arylsulfonylhydrazrones (**31**) \\ (Method 2.9) \\ \end{tabular} & \multirow{2}{*}{\(p\)-NO\({}_{2}\)C\({}_{6}\)H\({}_{4}\)} & 1. NCS, KOH, CH\({}_{3}\)NO\({}_{2}\), & & & \\  & & & 0 \({}^{\circ}\)C & & \\ \end{tabular}
\end{table} 
Table 3: Summary of other precursors and conditions for the construction of the 1,2,4,5-tetrazine ring. Recent efforts have focused on designing new HEDM compounds with the highest possible density, as density influences potential energy (\(E\)) and other parameters such as detonation pressure (\(P\)) and detonation velocity (\(D\)). The detonation velocity and detonation pressure are correlated with density (\(\rho\)) through the Kamlet-Jacobs equations (Formulas (1) and (2)). \[D=1.01\varphi^{0.5}(1+1.30\rho) \tag{1}\]  
Formula (1). Kamlet-Jacobs equation for detonation velocity (\(D\), km/s). \[P=15.58\varphi\rho^{2} \tag{2}\]  
Formula (2). Kamlet-Jacobs equation for detonation velocity (\(P\), kbar). Detonation parameters depend not only on density but also on the detonation parameter (\(\varphi\)), as described in Formula (3):  
\[\varphi=NM_{ave}^{0.5}Q^{0.5} \tag{3}\]  
Formula (3). Equation for the detonation parameter (\(\varphi\)). The parameter \(\varphi\) is influenced by the number of moles of gaseous detonation products per gram of explosive (N), the average molar mass of gaseous products (\(M_{ave}\), g/mol), and the total heat released during detonation (Q), expressed in calories per gram of explosive (Q) [89]. Generally, for substances composed of carbon and hydrogen atoms, a critical density value of approximately 2.00 g/cm\({}^{3}\) poses a challenge for achieving higher density while maintaining stability under normal conditions [90]. Table 4 presents the detonation parameters of the selected high energy density materials.