Both X-ray crystallography and electronic structure calculations using the cc-pVDZ basis set at the DFT B3LYP level were employed to study the explosive properties of triacetone triperoxide (TATP) and diacetone diperoxide (DADP). The thermal decomposition pathway of TATP was investigated by a series of calculations that identified transition states, intermediates, and the final products. Counterintuitively, these calculations predict that the explosion of TATP is not a thermochemically highly favored event. It rather involves entropy burst, which is the result of formation of one ozone and three acetone molecules from every molecule of TATP in the solid state.

Figure S1: Time evolution of main species for 1800K and 3500K at 0.7V0 Scheme S1: Hydrogen transfer routes between TNT and TNT-H and the cleavage of C-NO 2 from TNT molecule missing a ring bound hydrogen. Units: kcal/mol. S4 Scheme S2: Reactions of TNT radical missing a NO 2 group (TNT-NO 2). Units: kcal/mol. S5 Scheme S3. Total energies for ortho hydrogen transfer (top part) and further decomposition routes (bottom part). Units: kcal/mol.

To study the initial chemical events related to the detonation of triacetonetriperoxide (TATP), we have performed a series of molecular dynamics (MD) simulations. In these simulations we used the ReaxFF reactive force field, which we have extended to reproduce the quantum mechanics (QM)-derived relative energies of the reactants, products, intermediates, and transition states related to the TATP unimolecular decomposition. We find excellent agreement between the QM-predicted reaction products and those observed from 100 independent ReaxFF unimolecular MD cookoff simulations. Furthermore, the primary reaction products and average initiation temperature observed in these 100 independent unimolecular cookoff simulations match closely with those observed from a TATP condensed-phase cookoff simulation, indicating that unimolecular decomposition dominates the thermal initiation of the TATP condensed phase. Our simulations demonstrate that thermal initiation of condensed-phase TATP is entropy-driven (rather than enthalpy-driven), since the initial reaction (which mainly leads to the formation of acetone, O(2), and several unstable C(3)H(6)O(2) isomers) is almost energy-neutral. The O(2) generated in the initiation steps is subsequently utilized in exothermic secondary reactions, leading finally to formation of water and a wide range of small hydrocarbons, acids, aldehydes, ketones, ethers, and alcohols.

Vapors of chemical substances may be detected with a solid-state sensor coated with a layer that selectively and specifically forms a bond with the vapor, leading to changes in the physicochemical properties of the sensor device. Triacetone triperoxide (TATP) is a homemade explosive that may evade detection by most commonly used detectors but could be detected by a sensor with the proper coating. The conformation and the strength of the bond formed between TATP and several ionsLi+, Cu+, Zn2+, Cd2+, In3+, Sb3+, Sc3+, and Ti4+have been calculated by quantum chemical methods. It was found that of the ions tested in the present work the bonds formed between TATP and Zn2+ and In3+ were the strongest and the interaction with Sb3+, Sc3+, and Ti4+ leads to cleavage of the TATP ring. Thus, in principle, a coating with a suitable ion may serve as the key element for detection of concealed TATP.

Ring expansion processes in 1-, 2-, and 5-methylenecyclopentadiene radicals and isomerizations among the three isomers were studied by the Becke three-parameter hybrid method with Lee-Yang-Parr correlation functional approximation (B3LYP). Structure, energy, and frequency calculations were carried out with the Dunning correlation consistent polarized double (cc-pVDZ) and augmented aug-cc-pVDZ basis sets. The potential energy surfaces for ring expansion in methylenecyclopentadiene radicals consist of several intermediates and transition states. The process that takes place by insertion of the methylene group into the cyclopentadiene ring in the three isomers occurs via two principal mechanisms. One mechanism is associated with cleavage of the five-membered ring of the cyclopentadiene ring. In the second mechanism, the transition states of the first stage consist of a newly formed three-membered ring fused to the original cyclopentadiene ring. In all the three isomers of methylenecyclopentadiene, the reaction pathways leading to ring expansion include intermediates that via additional transition states lead to the production of the cyclohexadienyl radical. The latter, by a very fast H-atom ejection produces benzene. The structure and energetics of the various pathways are shown. The isomerization processes 1-methylenecyclopentadiene S 5-methylenecyclopentadiene and 2-methylenecyclopentadiene S 1-methylenecyclopentadiene involve a single 1,2-H atom shift and proceeds in one step without intermediates. The ring expansion in 1-methylenecyclopentadiene proceeds much faster via isomerization to 5-methylenecyclopentadiene than via direct formation of cyclohexadienyl.