Multispin Entangled Polyradical Roaming Reactions from Spin-Symmetry Breakings and Aromatic Ring Fission in Nitroaromatic Energetic Molecules.

Roaming, as an unconventional and ubiquitous class of reaction processes that bypass the minimum energy path (MEP), has increasingly become essential for understanding and regulating chemical reactions. In this context, despite the emerging consensus on the spin-polarized diradical roaming model for energetic molecules, it remains elusive to elucidate complex energy transfer and release processes, necessitating a deep insight into roaming radicals and their contributions to reactivity. Herein, we report the discovery of polyradical roaming reactions in a nitroaromatic energetic prototype, 2,4,6-trinitrotoluene (TNT). High-level ab initio calculations show that one-step polyradical roaming reaction yields NO molecules required for two-step MEP, with an energy barrier commensurate with that of the conventional two-step MEP. In particular, these polyradical systems formed during this reaction exhibit multispin entanglement arising from spin-symmetry breakings and aromatic ring fission, along with a nontrivial arrangement of ferromagnetic and antiferromagnetic coupling on distinct radicals, corroborated by many-body electronic structure calculations. Rate constant analyses then reveal that the contribution of the roaming reaction to the thermal dissociation is comparable to MEP for NO formation at detonation, underscoring its mechanistic significance. Such polyradical roaming reactions beyond diradical are also identified in other nitroaromatic energetic molecules, including 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitroaniline (MATB), suggesting that polyradical roaming might be an emerging reaction mechanism in nitroaromatic decomposition.