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IUPAC name Dibenzo[ghi,mno]fluoranthene [1] | |
Other names [5]circulene; Buckybowl | |
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3D model (JSmol) | |
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PubChem CID | |
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CompTox Dashboard (EPA) | |
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Properties | |
C 20 H 10 | |
Molar mass | 250.29 g/mol |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Corannulene is a polycyclic aromatic hydrocarbon with chemical formula C 20 H 10. [2] The molecule consists of a cyclopentane ring fused with 5 benzene rings, so another name for it is [5]circulene. It is of scientific interest because it is a geodesic polyarene and can be considered a fragment of buckminsterfullerene. Due to this connection and also its bowl shape, corannulene is also known as a buckybowl. Buckybowls are fragments of buckyballs. Corannulene exhibits a bowl-to-bowl inversion with an inversion barrier of 10.2 kcal/mol (42.7 kJ/mol) at −64 °C. [3]
Several synthetic routes exist to corannulene. Flash vacuum pyrolysis techniques generally have lower chemical yields than solution-chemistry syntheses, but offer routes to more derivatives. Corannulene was first isolated in 1966 by multistep organic synthesis. [4] In 1971, the synthesis and properties of corannulane were reported. [5] A flash vacuum pyrolysis method followed in 1991. [6] One synthesis based on solution chemistry [7] consists of a nucleophilic displacement – elimination reaction of an octabromide with sodium hydroxide:
The bromine substituents are removed with an excess of n-butyllithium.
A kilogram scale synthesis of corannulene has been achieved. [8]
Much effort is directed at functionalization of the corannulene ring with novel functional groups such as ethynyl groups, [3] [9] [10] ether groups, [11] thioether groups, [12] platinum functional groups, [13] aryl groups, [14] phenalenyl fused [15] and indeno extensions. [16] and ferrocene groups. [17]
The observed aromaticity for this compound is explained with a so-called annulene-within-an-annulene model. According to this model corannulene is made up of an aromatic 6 electron cyclopentadienyl anion surrounded by an aromatic 14 electron annulenyl cation. This model was suggested by Barth and Lawton in the first synthesis of corannulene in 1966. [4] They also suggested the trivial name 'corannulene', which is derived from the annulene-within-an-annulene model: core + annulene.
However, later theoretical calculations have disputed the validity of this approximation. [18] [19]
Corannulene can be reduced up to a tetraanion in a series of one-electron reductions. This has been performed with alkali metals, electrochemically and with bases. The corannulene dianion is antiaromatic and tetraanion is again aromatic. With lithium as reducing agent two tetraanions form a supramolecular dimer with two bowls stacked into each other with 4 lithium ions in between and 2 pairs above and below the stack. [20] This self-assembly motif was applied in the organization of fullerenes. Penta-substituted fullerenes (with methyl or phenyl groups) charged with five electrons form supramolecular dimers with a complementary corannulene tetraanion bowl, 'stitched' by interstitial lithium cations. [21] In a related system 5 lithium ions are sandwiched between two corannulene bowls [22]
In one cyclopenta[bc]corannulene a concave - concave aggregate is observed by NMR spectroscopy with 2 C–Li–C bonds connecting the tetraanions. [23]
Metals tend to bind to the convex face of the annulene. Concave binding has been reported for a cesium / crown ether system [24]
UV 193-nm photoionization effectively removes a π-electron from the twofold degenerate E1-HOMO located in the aromatic network of electrons yielding a corannulene radical cation. [25] Owing to the degeneracy in the HOMO orbital, the corannulene radical cation is unstable in its original C5v molecular arrangement, and therefore, subject to Jahn-Teller (JT) vibronic distortion.
Using electrospray ionization, a protonated corannulene cation has been produced in which the protonation site was observed to be on a peripheral sp2-carbon atom. [25]
Corannulene can react with electrophiles to form a corannulene carbocation. Reaction with chloromethane and aluminium chloride results in the formation of an AlCl4− salt with a methyl group situated at the center with the cationic center at the rim. X-ray diffraction analysis shows that the new carbon-carbon bond is elongated (157 pm) [26]
Bicorannulenyl is the product of dehydrogenative coupling of corannulene. With the formula C20H9-C20H9, it consists of two corannulene units connected through a single C-C bond. The molecule's stereochemistry consists of two chiral elements: the asymmetry of a singly substituted corannulenyl, and the helical twist about the central bond. In the neutral state, bicorannulenyl exists as 12 conformers, which interconvert through multiple bowl-inversions and bond-rotations. [27] When bicorannulenyl is reduced to a dianion with potassium metal, the central bond assumes significant double-bond character. This change is attributed to the orbital structure, which has a LUMO orbital localized on the central bond. [28] When bicorannulenyl is reduced to an octaanion with lithium metal, it self-assembles into supramolecular oligomers. [29] This motif illustrates "charged polyarene stacking".
The corannulene group is used in host–guest chemistry with interactions based on pi stacking, notably with fullerenes (the buckycatcher) [30] [31] but also with nitrobenzene [32]
Alkyl-substituted corannulenes form a thermotropic hexagonal columnar liquid crystalline mesophase. [33] Corannulene has also been used as the core group in a dendrimer. [14] Like other PAHs, corannulene ligates metals. [34] [35] [36] [37] [38] [39] [40] Corannulenes with ethynyl groups are investigated for their potential use as blue emitters. [10] The structure was analyzed by infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. [41]
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
In organic chemistry, Hückel's rule predicts that a planar ring molecule will have aromatic properties if it has 4n + 2 π-electrons, where n is a non-negative integer. The quantum mechanical basis for its formulation was first worked out by physical chemist Erich Hückel in 1931. The succinct expression as the 4n + 2 rule has been attributed to W. v. E. Doering (1951), although several authors were using this form at around the same time.
A silabenzene is a heteroaromatic compound containing one or more silicon atoms instead of carbon atoms in benzene. A single substitution gives silabenzene proper; additional substitutions give a disilabenzene, trisilabenzene, etc.
In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a non-carbon radical anion is the superoxide anion, formed by transfer of one electron to an oxygen molecule. Radical anions are typically indicated by .
1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of its stoichiometric relationship to benzene, COT has been the subject of much research and some controversy.
Cyclodecapentaene or [10]annulene is an annulene with molecular formula C10H10. This organic compound is a conjugated 10 pi electron cyclic system and according to Huckel's rule it should display aromaticity. It is not aromatic, however, because various types of ring strain destabilize an all-planar geometry.
Cyclooctadecanonaene or [18]annulene is an organic compound with chemical formula C
18H
18. It belongs to the class of highly conjugated compounds known as annulenes and is aromatic. The usual isomer that [18]annulene refers to is the most stable one, containing six interior hydrogens and twelve exterior ones, with the nine formal double bonds in the cis,trans,trans,cis,trans,trans,cis,trans,trans configuration. It is reported to be a red-brown crystalline solid.
In organic chemistry, annulynes or dehydroannulenes are conjugated monocyclic hydrocarbons with alternating single and double bonds in addition to at least one triple bond.
An aromatic ring current is an effect observed in aromatic molecules such as benzene and naphthalene. If a magnetic field is directed perpendicular to the plane of the aromatic system, a ring current is induced in the delocalized π electrons of the aromatic ring. This is a direct consequence of Ampère's law; since the electrons involved are free to circulate, rather than being localized in bonds as they would be in most non-aromatic molecules, they respond much more strongly to the magnetic field.
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
Fullerene chemistry is a field of organic chemistry devoted to the chemical properties of fullerenes. Research in this field is driven by the need to functionalize fullerenes and tune their properties. For example, fullerene is notoriously insoluble and adding a suitable group can enhance solubility. By adding a polymerizable group, a fullerene polymer can be obtained. Functionalized fullerenes are divided into two classes: exohedral fullerenes with substituents outside the cage and endohedral fullerenes with trapped molecules inside the cage.
A geodesic polyarene in organic chemistry is a polycyclic aromatic hydrocarbon with curved convex or concave surfaces. Examples include fullerenes, nanotubes, corannulenes, helicenes and sumanene. The molecular orbitals of the carbon atoms in these systems are to some extent pyramidalized resulting a different pi electron density on either side of the molecule with consequences for reactivity.
Cyclododecahexaene or [12]annulene is a member of the series of annulenes with some interest in organic chemistry with regard to the study of aromaticity. Cyclododecahexaene is non-aromatic due to the lack of planarity of the structure. On the other hand the dianion with 14 electrons is a Hückel aromat and more stable.
The reduction of nitro compounds are chemical reactions of wide interest in organic chemistry. The conversion can be effected by many reagents. The nitro group was one of the first functional groups to be reduced. Alkyl and aryl nitro compounds behave differently. Most useful is the reduction of aryl nitro compounds.
Rhodizonic acid is a chemical compound with formula H2C6O6 or (CO)4(COH)2. It can be seen as a twofold enol and fourfold ketone of cyclohexene, more precisely 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone.
The Birch reduction is an organic reaction that is used to convert arenes to 1,4-cyclohexadienes. The reaction is named after the Australian chemist Arthur Birch and involves the organic reduction of aromatic rings in an amine solvent with an alkali metal and a proton source. Unlike catalytic hydrogenation, Birch reduction does not reduce the aromatic ring all the way to a cyclohexane.
Octalene is a polycyclic hydrocarbon composed of two fused cyclooctatetraene rings.
Thermal rearrangements of aromatic hydrocarbons are considered to be unimolecular reactions that directly involve the atoms of an aromatic ring structure and require no other reagent than heat. These reactions can be categorized in two major types: one that involves a complete and permanent skeletal reorganization (isomerization), and one in which the atoms are scrambled but no net change in the aromatic ring occurs (automerization). The general reaction schemes of the two types are illustrated in Figure 1.
Bis(cyclopentadienyl)titanium(III) chloride, also known as the Nugent–RajanBabu reagent, is the organotitanium compound which exists as a dimer with the formula [(C5H5)2TiCl]2. It is an air sensitive green solid. The complex finds specialized use in synthetic organic chemistry as a single electron reductant.
Lithium naphthalene is an organic salt with the chemical formula Li+[C10H8]−. In the research laboratory, it is used as a reductant in the synthesis of organic, organometallic, and inorganic chemistry. It is usually generated in situ. Lithium naphthalene crystallizes with ligands bound to Li+. The anion is a well-known example of an organic radical.