Bonding analysis of the effect of strain on trigger bonds in organic-cage energetic materials

• Published in: Theoretical chemistry accounts 2020-06, Vol.139 (6), Article 95
• Main Authors: Bayse, Craig A., Jaffar, Mohammad
• Format: Article
• Language: English
• Subjects: Atomic/Molecular Structure and Spectra; Bonding strength; Cage molecules; Chemical bonds; Chemistry; Chemistry and Materials Science; Covalent bonds; Energetic materials; Hydrocarbons; Inorganic Chemistry; Nitrogen dioxide; Organic Chemistry; Physical Chemistry; Regular Article; Substitutes; Theoretical and Computational Chemistry
• ISSN: 1432-881X; 1432-2234
• DOI: 10.1007/s00214-020-02604-0

Wiberg bond index and natural bond orbital analyses were used to examine the effect of strain on trigger bonds for a series of organic-cage molecules. In substituted cage hydrocarbons, weakening of the interior C–C bonds and strengthening of exterior C–X bonds are explained in terms of the contributions of the carbon 2 s and 2 p atomic orbitals to the bonds. The interior C–C, rather than C–NO 2 , bonds are expected to break to initiate explosive decomposition in nitro-substituted tetrahedranes, prismanes, and cubanes. Activation of C–C bonds in cage molecules increases with nitro substitution, but persubstituted cages are not necessarily the most activated. For example, heptanitrocubane is predicted to be more sensitive than octanitrocubane, consistent with experimental studies. In contrast, for a series of hypothetical nitroester substituted prismanes, the strengthening of the exterior C–ONO 2 bond weakens the O–NO 2 bond more than the interior C–C bonds. In CL-20 and TEX, cage strain as determined by WBI analysis in the fused five- and six-membered rings is less significant than for the cage hydrocarbon. In these known energetic materials, the N–NO 2 trigger bonds are activated by the orientation of the nitro groups.