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Hexazine (also known as hexaazabenzene) is a hypothetical
allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...
of
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...
composed of 6 nitrogen atoms arranged in a ring-like structure analogous to that of
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
. It would be the final member of the azabenzene (azine) series, in which all of the
methine group In organic chemistry, a methine group or methine bridge is a trivalent functional group , derived formally from methane. It consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen. ...
s of the benzene molecule have been replaced with nitrogen atoms. The two last members of this series, hexazine and
pentazine Pentazine is a hypothetical compound that consists of a six-membered aromatic ring containing five nitrogen atoms with the molecular formula C H N5. The name ''pentazine'' is used in the nomenclature of derivatives of this compound. Pentazine ...
, have not been observed, although all other members of the azine series have (such as
pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with ...
,
pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The othe ...
,
pyridazine Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula . It contains a six-membered ring with two adjacent nitrogen atoms. It is a colorless liquid with a boiling point of 208 °C. It is isomeric with two other ...
,
pyrazine Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-lik ...
,
triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but ...
s, and
tetrazine Tetrazine is a compound that consists of a six-membered aromatic ring containing four nitrogen atoms with the molecular formula C2 H2 N4. The name ''tetrazine'' is used in the nomenclature of derivatives of this compound. Three core-ring isomer ...
s).


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 In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satu ...
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 pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...
s on the nitrogen atoms, which may repel each other electrostatically and/or cause electron-donation to sigma antibonding orbitals.


See also

* 6-membered rings with other numbers of nitrogen atoms:
pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with ...
s,
diazine In organic chemistry, diazines are a group of organic compounds having the molecular formula . Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen. There are three structural isomers: * pyrida ...
s,
triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but ...
s,
tetrazine Tetrazine is a compound that consists of a six-membered aromatic ring containing four nitrogen atoms with the molecular formula C2 H2 N4. The name ''tetrazine'' is used in the nomenclature of derivatives of this compound. Three core-ring isomer ...
s, and (like hexazine, theoretical)
pentazine Pentazine is a hypothetical compound that consists of a six-membered aromatic ring containing five nitrogen atoms with the molecular formula C H N5. The name ''pentazine'' is used in the nomenclature of derivatives of this compound. Pentazine ...
s * Azide *
Pentazole Pentazole is an aromatic molecule consisting of a five-membered ring with all nitrogen atoms, one of which is bonded to a hydrogen atom. It has the molecular formula . Although strictly speaking a homocyclic, inorganic compound, pentazole has ...
(HN5) * Other molecular
allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...
s of nitrogen:
tetranitrogen Tetranitrogen is a neutrally charged polynitrogen allotrope of the chemical formula and consists of four nitrogen atoms. The tetranitrogen cation is the positively charged ion, , which is more stable than the neutral tetranitrogen molecule and i ...
(N4),
octaazacubane Octaazacubane is a hypothetical explosive allotrope of nitrogen with formula N8, whose molecules have eight atoms arranged into a cube. (By comparison, nitrogen usually occurs as the diatomic molecule N2.) It can be regarded as a cubane-type c ...
(N8) * Other inorganic benzene analogues:
borazine Borazine, also known as borazole, is a non-polar inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For thi ...
, hexaphosphabenzene


References


Further reading

* * * *


External links

*{{Commonscatinline Azines (heterocycles) Aromatic compounds Hypothetical chemical compounds Allotropes of nitrogen Six-membered rings