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【JPCL】氮五环炸药结构稳定与储能机制:氢键、超氢键和反氢键耦合

已有 1505 次阅读 2019-12-12 21:37 |个人分类:控键工程|系统分类:论文交流

Stabilization of the Dual-Aromatic Cyclo-N5ˉ Anion by Acidic Entrapment

Lei Zhang, Chuang Yao, Yi Yu, Sheng-Li Jiang, Chang Q Sun, Jun Chen

J. Phys. Chem. Lett. 2019, 10, 10, 2378-2385

https://doi.org/10.1021/acs.jpclett.9b01047  JPCL-5N.pdf


Pentazole anion, the best candidate for full-nitrogen energetic materials, can be isolated only from acidic solution for unclear reasons, which hinders the high-yield realization of a full-nitrogen substance with higher energy density. Herein, we report for the first time the discovery of the dual aromaticity (π and σ) of cyclo-N5, which makes the anion unstable in nature but confers additional stability in acidic surroundings. In addition to the usual π-aromaticity, similar to that of the prototypical benzene, five lone pairs are delocalized in the equatorial plane of cyclo-N5, forming additional σ-aromaticity. It is the compatible coexistence of the inter-lone-pair repulsion and inter-lone-pair attraction within the σ-aromatic system that makes the naked cyclo-N5 highly reactive to electrophiles and easily broken. Only in sufficiently acid solution can the cyclo-N5 become unsusceptible to the electrophilic attack and gain extra stability through the formation of hydrogen-bonded complex from surrounding electrophiles; otherwise, the cyclo-N5 cannot be productively isolated. The dual aromaticity discovered in cyclo-N5 is expected to be universal for pnictogen five-membered ring systems.


Abstract Imageimage.png

  1. N sp2轨道杂化:环内N:=:N孤对(超氢键)排斥使其失稳,所以五环仅在富质子酸性环境中稳定;

  2. 3H-3H 排斥(反氢键)拉伸N:H-O氢键使H-O缩短并弱化N:=:N排斥并导致N-N共价键缩短,储能。


    Ref:

    Jiang, C. et al. Response to Comment on "Synthesis and characterization of the pentazolate anion cyclo-N5 in (N5)6(H3O)3(NH4)4Cl.". Science 359, eaas8953 (2018).

    Zhang, C., Sun, C., Hu, B., Yu, C. & Lu, M. Synthesis and characterization of the pentazolate anion cyclo-N5 in (N5)6(H3O)3(NH4)4Cl. Science 355, 374 (2017).



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