Trigger bond analysis of nitroaromatic energetic materials using wiberg bond indices

• Published in: Journal of computational chemistry 2018-07, Vol.39 (19), p.1236-1248
• Main Authors: Shoaf, Ashley L., Bayse, Craig A.
• Format: Article
• Language: English
• Subjects: Bond strength; Bonding strength; Chemical bonds; Clean energy; Deactivation; density functional theory; Energetic materials; energetic properties; Flux density; Hydrogen; Hydrogen bonding; Hydrogen bonds; Molecular chains; Nitrogen dioxide; Phenols; Sensitivity; Steric effects; Sustainable development; trigger bonds; Wiberg bond index
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.25186

The identification of trigger bonds, bonds that break to initiate explosive decomposition, using computational methods could help direct the development of novel, “green” and efficient high energy density materials (HEDMs). Comparing bond densities in energetic materials to reference molecules using Wiberg bond indices (WBIs) provides a relative scale for bond activation (%ΔWBIs) to assign trigger bonds in a set of 63 nitroaromatic conventional energetic molecules. Intramolecular hydrogen bonding interactions enhance contributions of resonance structures that strengthen, or deactivate, the CNO2 trigger bonds and reduce the sensitivity of nitroaniline‐based HEDMs. In contrast, unidirectional hydrogen bonding in nitrophenols strengthens the bond to the hydrogen bond acceptor, but the phenol lone pairs repel and activate an adjacent nitro group. Steric effects, electron withdrawing groups and greater nitro dihedral angles also activate the CNO2 trigger bonds. %ΔWBIs indicate that nitro groups within an energetic molecule are not all necessarily equally activated to contribute to initiation. %ΔWBIs generally correlate well with impact sensitivity, especially for HEDMs with intramolecular hydrogen bonding, and are a better measure of trigger bond strength than bond dissociation energies (BDEs). However, the method is less effective for HEDMs with significant secondary effects in the solid state. Assignment of trigger bonds using %ΔWBIs could contribute to understanding the effect of intramolecular interactions on energetic properties. © 2018 Wiley Periodicals, Inc. Trigger bonds in energetic materials are proposed to initiate explosive decomposition using Wiberg bond indices. Steric effects and repulsion induce twists that activate nitros but hydrogen bonds enhance stability. Unidirectional OH hydrogen bonding deactivates the nitro involved in hydrogen bonding but activates the nitro with lone pair repulsion. %ΔWBIs can assign trigger bonds to help interpret impact sensitivities.