circulene
{{Short description|Class of chemical}}
A circulene is a macrocyclic arene in which a central polygon is surrounded and fused by benzenoids.{{cite journal | last1 = Dopper | first1 = J.H. | last2 = Wynberg | first2 = Hans | year = 1972 | title = Heterocirculenes a new class of polycyclic aromatic hydrocarbons | journal = Tetrahedron Letters | volume = 13 | issue = 9| pages = 763–766 | doi = 10.1016/S0040-4039(01)84432-4 }} Nomenclature within this class of molecules is based on the number of benzene rings surrounding the core, which is equivalent to the size of the central polygon. Examples which have been synthesized include [5]circulene (corannulene), [6]circulene (coronene), [7]circulene,{{cite journal | last1 = Yamamoto | first1 = Koji | last2 = Harada | first2 = Tadashi | last3 = Nakazaki | first3 = Masao | last4 = Naka | first4 = Takuo | last5 = Kai | first5 = Yasushi | last6 = Harada | first6 = Shigeharu | last7 = Kasai | first7 = Nobutami | year = 1983 | title = Synthesis and characterization of [7]circulene | journal = Journal of the American Chemical Society | volume = 105 | issue = 24| pages = 7171–7172 | doi = 10.1021/ja00362a025 }}{{cite journal | last1 = Koji | first1 = Yamamoto | last2 = Tadashi | first2 = Harada | last3 = Yoshio | first3 = Okamoto | last4 = Hiroaki | first4 = Chikamatsu | last5 = Masao | first5 = Nakazaki | last6 = Yasushi | first6 = Kai | last7 = Takuo | first7 = Nakao | last8 = Mitsuya | first8 = Tanaka | last9 = Shigeharu | first9 = Harada | last10 = Nobutami | first10 = Kasai | year = 1988 | title = Synthesis and molecular structure of [7]circulene | journal = Journal of the American Chemical Society | volume = 110 | issue = 11| pages = 3578–3584 | doi = 10.1021/ja00219a036 }}{{cite journal | last1 = Yamamoto | first1 = K. | last2 = Sonobe | first2 = H. | last3 = Matsubara | first3 = H. | last4 = Sato | first4 = M. | last5 = Okamoto | first5 = S. | last6 = Kitaura | first6 = K. | year = 1996 | title = Convenient New Synthesis of [7]Circulene | journal = Angew. Chem. Int. Ed. Engl. | volume = 35 | pages = 69–70 | doi = 10.1002/anie.199600691 }}Extended systems of closed helicene. Synthesis and characterization of [7] and [7.7]-circulene Koji Yamamoto Pure Appl. Chem., Vol. 65, No. 1, pp. 157-163, 1993. [http://www.iupac.org/publications/pac/1993/pdf/6501x0157.pdf Online article] and [12]circulene (kekulene) These compounds belong to a larger class of geodesic polyarenes. Whereas [5]circulene is bowl-shaped and [6]circulene is planar, [7]circulene has a unique saddle-shaped structure (compare to cones and partial cones in calixarenes). The helicenes are a conceptually related class of structures in which the array of benzene rings form an open helix rather than a closed ring.
Quadrannulene ([4]circulene)
The simple [4]circulene compound itself has not been synthesized, but a derivative, tetrabenzo[4]circulene, also called quadrannulene, has.{{cite journal | last1 = Bharat | first1 = Bhola | last2 = Bally | first2 = T. | last3 = Valente | first3 = A. | last4 = Cyrański | first4 = Michał K. | last5 = Dobrzycki | first5 = Ł. | last6 = Spain | first6 = Stephen M. | last7 = Rempała | first7 = P. | last8 = Chin | first8 = Matthew R. | last9 = King | first9 = Benjamin T. | year = 2010 | title = Quadrannulene: A Nonclassical Fullerene Fragment | url = http://doc.rero.ch/record/17178/files/bally_qnf.pdf| journal = Angew. Chem. Int. Ed. | volume = 49 | issue = 2| pages = 399–402 | doi = 10.1002/anie.200905633 | pmid = 19957259 }}
[8]Circulenes
The isolation of the [8]circulene derivative 2,5,6,9,10,13,14-octamethyl-3,4,7,8,11,12,15,16-octa(4-tolyl)[8]circulene has been reported.{{cite journal | last1 = Feng | first1 = C.-N. | last2 = Kuo | first2 = M.-Y. | last3 = Wu | first3 = Y.-T. | year = 2013 | title = Synthesis, Structural Analysis, and Properties of [8]Circulenes | journal = Angew. Chem. Int. Ed. | volume = 52 | issue = 30| pages = 7791–7794 | doi = 10.1002/anie.201303875 | pmid = 23794166 }}
Tetrabenzo[8]circulene (TB8C), a functionally stable form of the parent molecule [8]circulene has also been reported.{{cite journal|last1=Miller|first1=Robert|last2=Duncan|first2=Alexandra|last3=Schneebeli|first3=Severin|last4=Gray|first4=Danielle|last5=Whalley|first5=Adam|title=Synthesis and Structural Data of Tetrabenzo[8]circulene|journal=Chem. Eur. J.|date=24 February 2014|volume=20|issue=13|page=3711|doi=10.1002/chem.201304657|pmid=24615957|pmc=4371848}}{{cite journal|last1=Nakamoto|first1=Youichi|last2=Suzuki|first2=Toshiyasu|title=Tetrabenzo[8]circulene: Aromatic Saddles from Negatively Curved Graphene|journal=J. Am. Chem. Soc.|date=2013|volume=135|issue=38|pages=14074–7|doi=10.1021/ja407842z|pmid=24015972}}{{cite journal|last1=Miller|first1=Robert W.|last2=Averill|first2=Summer E.|last3=Van Wyck|first3=Stephen J.|last4=Whalley|first4=Adam C.|title=General Method for the Synthesis of Functionalized Tetrabenzo[8]circulenes|journal=The Journal of Organic Chemistry|date=2 December 2016|volume=81|issue=23|page=12005|doi=10.1021/acs.joc.6b02244|pmid=27934450}}
Heterocyclic circulenes
File:Sulflower-from-xtal-3D-balls.png, an octacirculene]]
A heterocyclic circulene is one in which the fused rings around the periphery are not simple hydrocarbons, but instead contain at least one other element. Sulflower is a stable heterocyclic octacirculene based on thiophene.
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Gallery
Image:Corannulene.svg|Corannulene ([5]circulene)
Image:Coronene 200.svg|Coronene ([6]circulene)
Image:-7-circulene.svg|[7]circulene
Image:Kekulene.svg|Kekulene ([12]circulene)