Enhanced detonation sensitivities of silicon analogs of PETN: reaction force analysis and the role of σ–hole interactions |
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Authors: | Jane S Murray Pat Lane Anian Nieder Thomas M Klapötke Peter Politzer |
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Institution: | (1) Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA;(2) Department of Chemistry and Biochemistry, Ludwig-Maximilian University of Munich, Butenandtstr. 5-13(D), 81377 Munich, Germany;(3) Departments of Mechanical Engineering and Chemistry/Biochemistry, CECD, University of Maryland, College Park, MD 20742, USA |
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Abstract: | Si-pentaerythritol tetranitrate (PETN), SiCH2ONO2]4, is a silicon analog of the widely used explosive PETN, CCH2ONO2]4. Si-PETN is extremely sensitive to impact, much more so than PETN. This was attributed by Liu et al. to Si-PETN having a
much lower activation barrier to decomposition, via a facile rearrangement that is not as readily available to PETN, and which
releases considerable energy that can promote further steps. We have investigated computationally why the barrier to the rearrangement
is so much lower for Si-PETN than for PETN, using 5, (H3C)3C–CH2ONO2, and 6, (H3C)3Si–CH2ONO2, as models for PETN and Si-PETN. Reaction force analysis shows that most of the difference between the rearrangement barriers
for 5 and 6 comes about in the initial (reactant) stages of the processes, in which 6 benefits from a 1,3 electrostatic interaction involving a positive σ–hole on the silicon and the negative linking oxygen.
The analogous interaction is weaker in 5, since the central carbon does not have positive σ–holes; furthermore, this carbon is less able than silicon to temporarily
expand its coordination sphere. A similar explanation involving a positive silicon σ–hole and a linking oxygen is proposed
for Si-PETN. The greater exothermicity of the rearrangement of 6 (and also Si-PETN) can be rationalized, following Liu et al., in terms of the formation of the strong Si–O bond. |
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