Hexazine (also known as hexaazabenzene) is a hypothetical allotrope of nitrogen composed of 6 nitrogen atoms arranged in a ring-like structure analogous to that of benzene. As a neutrally charged species, it would be the final member of the azabenzene (azine) series, in which all of the methine groups of the benzene molecule have been replaced with nitrogen atoms. The two last members of this series, hexazine and pentazine, have not been observed, although all other members of the azine series have (such as pyridine, pyrimidine, pyridazine, pyrazine, triazines, and tetrazines).
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| Names | |
|---|---|
| Preferred IUPAC name Hexazine (preselected name) | |
| Systematic IUPAC name Hexaazabenzene | |
| Other names | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| 1819 | |
PubChem CID |
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CompTox Dashboard (EPA) | |
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| Properties | |
| N6 | |
| Molar mass | 84.042 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
While a neutrally charged hexazine species has not yet been synthesized, two negatively charged variants, [N6]2-[2] and [N6]4-,[3] have been produced in potassium-nitrogen compounds under very high pressures (> 40 GPa) and temperatures (> 2000 K). In particular, [N6]4- is aromatic, respecting Hückel's rule, while [N6]2- is anti-aromatic.
Stability
The hexazine molecule bears a structural similarity to the very stable benzene molecule. Like benzene, it has been calculated that hexazine is likely an aromatic molecule. Despite this, it has yet to be synthesized. Additionally, it has been predicted computationally that the hexazine molecule is highly unstable, possibly due to the lone pairs on the nitrogen atoms, which may repel each other electrostatically and/or cause electron-donation to sigma antibonding orbitals. A figure-8-shaped isomer is predicted to be metastable.[4]
See also
- 6-membered rings with other numbers of nitrogen atoms: pyridines, diazines, triazines, tetrazines, and (like hexazine, theoretical) pentazines
- Azide
- Pentazole (HN5)
- Other molecular allotropes of nitrogen: tetranitrogen (N4), octaazacubane (N8)
- Other inorganic benzene analogues: borazine, hexaphosphabenzene
References
Further reading
- P. Saxe and H. F. Schaefer III (1983). "Cyclic D6h Hexaazabenzene-A Relative Minimum on the N6 Potential Energy Hypersurface?". Journal of the American Chemical Society. 105 (7): 1760–1764. doi:10.1021/ja00345a010.
- H. Huber (1982). "Is Hexazine Stable?". Angewandte Chemie International Edition. 21 (1): 64–65. doi:10.1002/anie.198200641.
- M. N. Glukhovtsev and P. von Ragué Schleyer (1992). "Structures, bonding and energies of N[6] isomers". Chemical Physics Letters. 198 (6): 547–554. Bibcode:1992CPL...198..547G. doi:10.1016/0009-2614(92)85029-A.
- T.-K. Ha, R. Cimiraglia and M.T. Nguyen (1981). "Can hexazine (N6) be stable?". Chemical Physics Letters. 83 (2): 317–319. Bibcode:1981CPL....83..317H. doi:10.1016/0009-2614(81)85471-1.
External links
Media related to Hexazine at Wikimedia Commons
