Cyclooctatetraene

Last updated
Cyclooctatetraene
Cyclooctatetraen.svg
Cyclooctatetraene-from-xtal-side-3D-bs-17.png
Cyclooctatetraene-from-xtal-top-3D-bs-17.png
Cyclooctatetraene-from-xtal-top-3D-sf.png
Names
Preferred IUPAC name
Cycloocta-1,3,5,7-tetraene [1]
Other names
[8]Annulene
(1Z,3Z,5Z,7Z)-Cycloocta-1,3,5,7-tetraene
1,3,5,7-Cyclooctatetraene
COT
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.010.074 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 211-080-3
PubChem CID
UNII
  • InChI=1S/C8H8/c1-2-4-6-8-7-5-3-1/h1-8H/b2-1-,3-1-,4-2-,5-3-,6-4-,7-5-,8-6-,8-7- Yes check.svgY
    Key: KDUIUFJBNGTBMD-BONZMOEMSA-N Yes check.svgY
  • InChI=1/C8H8/c1-2-4-6-8-7-5-3-1/h1-8H/b2-1-,3-1-,4-2-,5-3-,6-4-,7-5-,8-6-,8-7-
    Key: KDUIUFJBNGTBMD-BONZMOEMBR
  • C1=C\C=C/C=C\C=C1
Properties
C8H8
Molar mass 104.15 g/mol
AppearanceClear yellow
Density 0.9250 g/cm3, liquid
Melting point −5 to −3 °C (23 to 27 °F; 268 to 270 K)
Boiling point 142 to 143 °C (288 to 289 °F; 415 to 416 K)
immiscible
-53.9·10−6 cm3/mol
Hazards
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg
Danger
H225, H304, H315, H319, H335
P210, P233, P240, P241, P242, P243, P261, P264, P271, P280, P301+P310, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P312, P321, P331, P332+P313, P337+P313, P362, P370+P378, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
3
0
Flash point −11 °C (12 °F; 262 K)
561 °C (1,042 °F; 834 K)
Related compounds
Related hydrocarbons
Cyclooctane
Tetraphenylene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

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.

Contents

Unlike benzene, C6H6, cyclooctatetraene, C8H8, is not aromatic, although its dianion, C
8H2−
8 (cyclooctatetraenide), is. Its reactivity is characteristic of an ordinary polyene, i.e. it undergoes addition reactions. Benzene, by contrast, characteristically undergoes substitution reactions, not additions.

History

1,3,5,7-Cyclooctatetraene was initially synthesized by Richard Willstätter in Munich in 1905 using pseudopelletierine as the starting material and the Hofmann elimination as the key transformation: [2] [3]

Willstaetter Synthesis COT.svg

Willstätter noted that the compound did not exhibit the expected aromaticity. Between 1939 and 1943, chemists throughout the US unsuccessfully attempted to synthesize COT. They rationalized their lack of success with the conclusion that Willstätter had not actually synthesized the compound but instead its isomer, styrene. Willstätter responded to these reviews in his autobiography, where he noted that the American chemists were 'untroubled' by the reduction of his cyclooctatetraene to cyclooctane (a reaction impossible for styrene). During World War II, Walter Reppe at BASF Ludwigshafen developed a simple, one-step synthesis of cyclooctatetraene from acetylene, providing material identical to that prepared by Willstätter. [4] Any remaining doubts on the accuracy of Willstätter's original synthesis were resolved when Arthur C. Cope and co-workers at MIT reported, in 1947, a complete repetition of the Willstätter synthesis, step by step, using the originally reported techniques. They obtained the same cyclooctatetraene, [5] and they subsequently reported modern spectral characterization of many of the intermediate products, again confirming the accuracy of Willstätter's original work. [6] However, the freezing temperature of the product was different from pure COT, and the authors interpreted it as contamination with about 30% of styrene.

Structure and bonding

Cyclooctatetraene in its native "tub-shaped" conformation All-Z-Cyclooctatetraene 3D skeletal formula.svg
Cyclooctatetraene in its native "tub-shaped" conformation

Early studies demonstrated that COT did not display the chemistry of an aromatic compound. [7] Then, early electron diffraction experiments concluded that the C-C bond distances were identical. [8] However, X-ray diffraction data from H. S. Kaufman demonstrated cyclooctatetraene to adopt several conformations and to contain two distinct C–C bond distances. [9] This result indicated that COT is an annulene with fixed alternating single and double C-C bonds.

In its normal state, cyclooctatetraene is non-planar and adopts a tub conformation with angles C=C−C = 126.1° and C=C−H = 117.6°. [10] The point group of cyclooctatetraene is D2d. [11]

In its planar transition state, the D4h transitional state is more stable than the D8h transitional state due to the Jahn–Teller effect. [12]

Synthesis

Richard Willstätter's original synthesis (4 consecutive elimination reactions on a cyclooctane framework) gives relatively low yields. Reppe's synthesis of cyclooctatetraene, which involves treating acetylene at high pressure with a warm mixture of nickel cyanide and calcium carbide, was much better, with chemical yields near 90%: [4]

Reppe Synthesis COT.svg

COT can also be prepared by photolysis of barrelene, one of its structural isomers, the reaction proceeding via another isolable isomer, semibullvalene. [13] COT derivatives can also be synthesised by way of semibullvalene intermediates. In the sequence illustrated below, octaethylcyclooctatetraene (C8 Et 8) is formed by thermal isomerisation of octaethylsemibullvalene, itself formed by copper(I) bromide mediated cyclodimerisation of 1,2,3,4-tetraethyl-1,4-dilithio-1,3-butadiene. [14]

NewSemibullvaleneSynthesis.png

Because COT is unstable and easily forms explosive organic peroxides, a small amount of hydroquinone is usually added to commercially available material. Testing for peroxides is advised when using a previously opened bottle; white crystals around the neck of the bottle may be composed of the peroxide, which may explode when mechanically disturbed.

Natural occurrence

Cyclooctatetraene has been isolated from certain fungi. [15]

Reactions

The π bonds in COT react as usual for olefins, rather than as aromatic ring systems. Mono- and polyepoxides can be generated by reaction of COT with peroxy acids or with dimethyldioxirane. Various other addition reactions are also known. Furthermore, polyacetylene can be synthesized via the ring-opening polymerization of cyclooctatetraene. [16] COT itself—and also analogs with side-chains—have been used as metal ligands and in sandwich compounds.

Cyclooctatetraene also undergoes rearrangement reactions to form aromatic ring systems. For instance, oxidation with aqueous mercury(II) sulfate forms phenylacetaldehyde [4] [17] and photochemical rearrangement of its monoepoxide forms benzofuran. [18]

Cyclooctatetraenide as a ligand and ligand precursor

Ball-and-stick model of COT Cyclooctatetraenide-3D-ball.png
Ball-and-stick model of COT

COT readily reacts with potassium metal to form the salt K2COT, which contains the dianion C
8H2−
8. [19] The dianion is planar, octagonal, and aromatic with a Hückel electron count of 10.

Cyclooctatetraene forms organometallic complexes with some metals, including yttrium, lanthanides, and actinides. [20] The sandwich compound uranocene (U(COT)2) features two η8-COT ligands. In bis(cyclooctatetraene)iron (Fe(COT)2) one COT is η6 and the other is η4. (Cyclooctatetraene)iron tricarbonyl features η4-COT. The room-temperature 1H NMR spectra of these iron complexes are singlets, indicative of fluxionality. [21]

Uranocene, a sandwich compound containing two COT rings. Uranocene-3D-vdW.png
Uranocene, a sandwich compound containing two COT rings.

Cyclooctatetraene is chlorinated to give a [4.2.0]-bicyclic compound, which reacts further with dimethyl acetylenedicarboxylate in a Diels-Alder reaction (DA). Retro-DA at 200 °C releases cis-dichlorocyclobutene. This compound reacts with diiron nonacarbonyl to give cyclobutadieneiron tricarbonyl. [22] [23]

CyclobutadieneirontricarbonylSynthesis.png

See also

Related Research Articles

<span class="mw-page-title-main">Aromaticity</span> Chemical property

In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August Wilhelm Hofmann in 1855. There is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds.

<span class="mw-page-title-main">Polyacetylene</span> Organic polymer made of the repeating unit [C2H2]

Polyacetylene usually refers to an organic polymer with the repeating unit [C2H2]n. The name refers to its conceptual construction from polymerization of acetylene to give a chain with repeating olefin groups. This compound is conceptually important, as the discovery of polyacetylene and its high conductivity upon doping helped to launch the field of organic conductive polymers. The high electrical conductivity discovered by Hideki Shirakawa, Alan Heeger, and Alan MacDiarmid for this polymer led to intense interest in the use of organic compounds in microelectronics. This discovery was recognized by the Nobel Prize in Chemistry in 2000. Early work in the field of polyacetylene research was aimed at using doped polymers as easily processable and lightweight "plastic metals". Despite the promise of this polymer in the field of conductive polymers, many of its properties such as instability to air and difficulty with processing have led to avoidance in commercial applications.

<span class="mw-page-title-main">Hückel's rule</span> Method of determining aromaticity in organic molecules

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.

Antiaromaticity is a chemical property of a cyclic molecule with a π electron system that has higher energy, i.e., it is less stable due to the presence of 4n delocalised electrons in it, as opposed to aromaticity. Unlike aromatic compounds, which follow Hückel's rule and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions. In contrast to the diamagnetic ring current present in aromatic compounds, antiaromatic compounds have a paramagnetic ring current, which can be observed by NMR spectroscopy.

<span class="mw-page-title-main">Pentalene</span> Chemical compound

Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula C8H6. It is antiaromatic, because it has 4n π electrons where n is any integer. For this reason it dimerizes even at temperatures as low as −100 °C. The derivative 1,3,5-tri-tert-butylpentalene was synthesized in 1973. Because of the tert-butyl substituents this compound is thermally stable. Pentalenes can also be stabilized by benzannulation for example in the compounds benzopentalene and dibenzopentalene.

<span class="mw-page-title-main">Silabenzene</span> Chemical compound

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.

An alkyne trimerisation is a [2+2+2] cycloaddition reaction in which three alkyne units react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applicable to organic synthesis. Being a cycloaddition reaction, it has high atom economy. Many variations have been developed, including cyclisation of mixtures of alkynes and alkenes as well as alkynes and nitriles.

Cycloheptatriene (CHT) is an organic compound with the formula C7H8. It is a closed ring of seven carbon atoms joined by three double bonds (as the name implies) and four single bonds. This colourless liquid has been of recurring theoretical interest in organic chemistry. It is a ligand in organometallic chemistry and a building block in organic synthesis. Cycloheptatriene is not aromatic, as reflected by the nonplanarity of the methylene bridge (-CH2-) with respect to the other atoms; however the related tropylium cation is.

<span class="mw-page-title-main">Cyclic compound</span> Molecule with a ring of bonded atoms

A cyclic compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon, none of the atoms are carbon, or where both carbon and non-carbon atoms are present. Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be aromatic or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size numbers in the many billions.

<span class="mw-page-title-main">Homoaromaticity</span> Organic molecular structure

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.

Bullvalene is a hydrocarbon with the chemical formula C10H10. The molecule has a cage-like structure formed by the fusion of one cyclopropane and three cyclohepta-1,4-diene rings. Bullvalene is unusual as an organic molecule due to the C−C and C=C bonds forming and breaking rapidly on the NMR timescale; this property makes it a fluxional molecule.

Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by Howard Zimmerman in 1960, the name derives from the resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels–Alder adduct of benzene and acetylene. Due to its unusual molecular geometry, the compound is of considerable interest to theoretical chemists.

<span class="mw-page-title-main">Organoactinide chemistry</span> Study of chemical compounds containing actinide-carbon bonds

Organoactinide chemistry is the science exploring the properties, structure, and reactivity of organoactinide compounds, which are organometallic compounds containing a carbon to actinide chemical bond.

<span class="mw-page-title-main">Walter Reppe</span> German chemist (1892-1969)

Walter Julius Reppe was a German chemist. He is notable for his contributions to the chemistry of acetylene.

<span class="mw-page-title-main">Möbius aromaticity</span>

In organic chemistry, Möbius aromaticity is a special type of aromaticity believed to exist in a number of organic molecules. In terms of molecular orbital theory these compounds have in common a monocyclic array of molecular orbitals in which there is an odd number of out-of-phase overlaps, the opposite pattern compared to the aromatic character to Hückel systems. The nodal plane of the orbitals, viewed as a ribbon, is a Möbius strip, rather than a cylinder, hence the name. The pattern of orbital energies is given by a rotated Frost circle (with the edge of the polygon on the bottom instead of a vertex), so systems with 4n electrons are aromatic, while those with 4n + 2 electrons are anti-aromatic/non-aromatic. Due to incrementally twisted nature of the orbitals of a Möbius aromatic system, stable Möbius aromatic molecules need to contain at least 8 electrons, although 4 electron Möbius aromatic transition states are well known in the context of the Dewar-Zimmerman framework for pericyclic reactions. Möbius molecular systems were considered in 1964 by Edgar Heilbronner by application of the Hückel method, but the first such isolable compound was not synthesized until 2003 by the group of Rainer Herges. However, the fleeting trans-C9H9+ cation, one conformation of which is shown on the right, was proposed to be a Möbius aromatic reactive intermediate in 1998 based on computational and experimental evidence.

<span class="mw-page-title-main">Organonickel chemistry</span> Branch of organometallic chemistry

Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds featuring nickel-carbon bonds. They are used as a catalyst, as a building block in organic chemistry and in chemical vapor deposition. Organonickel compounds are also short-lived intermediates in organic reactions. The first organonickel compound was nickel tetracarbonyl Ni(CO)4, reported in 1890 and quickly applied in the Mond process for nickel purification. Organonickel complexes are prominent in numerous industrial processes including carbonylations, hydrocyanation, and the Shell higher olefin process.

In organic chemistry, two molecules are valence isomers when they are constitutional isomers that can interconvert through pericyclic reactions.

<span class="mw-page-title-main">Dibenzopentalene</span> Chemical compound

Dibenzopentalene (dibenzo[a,e]pentalene or dibenzo[b,f]pentalene) is an organic compound and a hydrocarbon with formula C16H10. It is of some scientific interest as a stable derivative of the highly reactive antiaromatic pentalene by benzannulation. The first derivative was synthesised in 1912 by Brand. The parent compound was reported in 1952. The NICS value for the 5-membered rings is estimated at 7.4 ppm and that of the six-membered rings -9.8 ppm. Aromatic dicationic salts can be obtained by reaction with antimony pentafluoride in sulfuryl chloride. The dianion forms by reduction with lithium metal or deprotonation of 5,10-dihydroindeno[2,1-a]indene with two equivalents of butyllithium. The aromatic nature of the dianion has been confirmed by X-ray analysis. Another isomer of this compound exists called dibenzo[a,f]pentalene with one of the benzene rings positioned on the other available pentalene face.

<span class="mw-page-title-main">Bis(cyclooctatetraene)iron</span> Chemical compound

Bis(cyclooctatetraene)iron is an organoiron compound with the formula Fe(C8H8)2, abbreviated Fe(COT)2. It is an air-sensitive black solid that is soluble in diethyl ether and aromatic solvents. The compound decomposes in solution after a few days even under inert atmosphere. It has no known practical applications but has been studied as a soluble source of Fe(0).

<span class="mw-page-title-main">Tris(cyclooctatetraene)triiron</span> Chemical compound

Tris(cyclooctatetraene)triiron or Fe3(COT)3, also referred to as the Lavallo-Grubbs compound (after its discoverers) is an organoiron compound with the formula Fe3(C8H8)3. It is a pyrophoric, black crystalline solid, which is insoluble in common organic solvents.The compound represents a rare example of a hydrocarbon analogue of the well-known Triiron dodecacarbonyl (Fe3(CO)12), originally prepared by Dewar and Jones in the early 20th century.

References

  1. ↑ "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. P001–P004. doi:10.1039/9781849733069-FP001 (inactive 2024-06-05). ISBN   978-0-85404-182-4.{{cite book}}: CS1 maint: DOI inactive as of June 2024 (link)
  2. ↑ Mason, S. (February 1997). "The Science and Humanism of Linus Pauling (1901−1994)". Chem. Soc. Rev. 26: 29–39. doi:10.1039/CS9972600029.
  3. ↑ Richard Willstätter; Ernst Waser (1911). "Über Cyclo-octatetraen" [On cyclooctatetraene]. Berichte der Deutschen Chemischen Gesellschaft . 44 (3): 3423–3445. doi:10.1002/cber.191104403216.
  4. 1 2 3 Reppe, Walter; Schlichtin, Otto; Klager, Karl; Toepel, Tim (1948). "Cyclisierende Polymerisation von Acetylen. I. Über Cyclooctatetraen" [Ring-forming polymerization of acetylene. I. Cyclooctatetraene]. Justus Liebigs Annalen der Chemie . 560 (1): 1–92. doi:10.1002/jlac.19485600102.
  5. ↑ Cope, Arthur C.; Overberger, C. G. (1947). "The synthesis of cycloöctatetraene from pseudopelletierine". Journal of the American Chemical Society . 69 (4): 976. doi:10.1021/ja01196a513. PMID   20292490.
  6. ↑ Cope, Arthur C.; Overberger, C. G. (1947). "Cyclic Polyolefins. I. Synthesis of Cycloöctatetraene from Pseudopelletierine". Journal of the American Chemical Society . 70 (4): 1433–1437. doi:10.1021/ja01184a041. PMID   18915758.
  7. ↑ Johnson, A. W. (1947). "Organic Chemistry". Sci. Progr. 35 (139): 506–515. JSTOR   43413011.
  8. ↑ Bastiensen, O.; Hassel, O.; Langseth, A. (1947). "The 'Octa-Benzene', Cyclo-octatetraene (C8H8)". Nature . 160 (4056): 128. Bibcode:1947Natur.160..128B. doi: 10.1038/160128a0 .
  9. ↑ Kaufman, H. S.; Fankuchen, I.; H., Mark (1948). "Structure of Cyclo-octatetraene". Nature . 161 (4083): 165. Bibcode:1948Natur.161..165K. doi: 10.1038/161165a0 .
  10. ↑ Thomas, P. M.; Weber, A. (1978). "High resolution Raman spectroscopy of gases with laser sources. XIII – the pure rotational spectra of 1,3,5,7-cyclooctatetraene and 1,5-cyclooctadiene". J. Raman Spectr. 7 (6): 353–357. Bibcode:1978JRSp....7..353T. doi:10.1002/jrs.1250070614.
  11. ↑ Claus, K. H.; Krüger, C. (15 September 1988). "Structure of cyclooctatetraene at 129 K". Acta Crystallogr. C . 44 (9): 1632–1634. Bibcode:1988AcCrC..44.1632C. doi:10.1107/S0108270188005840.
  12. ↑ Nishinaga, Tohru; Ohmae, Takeshi; Iyoda, Masahiko (5 February 2010). "Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene". Symmetry. 2 (1): 76–97. Bibcode:2010Symm....2...76N. doi: 10.3390/sym2010076 .
  13. ↑ Zimmerman, H. E.; Grunewald, G. L. (1966). "The Chemistry of Barrelene. III. A Unique Photoisomerization to Semibullvalene" (PDF). J. Am. Chem. Soc. 88 (1): 183–184. doi:10.1021/ja00953a045.
  14. ↑ Wang, C.; Yuan, J.; Li, G.; Wang, Z.; Zhang, S.; Xi, Z. (2006). "Metal-Mediated Efficient Synthesis, Structural Characterization, and Skeletal Rearrangement of Octasubstituted Semibullvalenes". J. Am. Chem. Soc. 128 (14): 4564–4565. doi:10.1021/ja0579208. PMID   16594680.
  15. ↑ Stinson, M.; Ezra, D.; Hess, W. M.; Sears, J.; Strobel, G. (2003). "An endophytic Gliocladium sp. of Eucryphia cordifolia producing selective volatile antimicrobial compounds". Plant Sci. 165 (4): 913–922. Bibcode:2003PlnSc.165..913S. doi:10.1016/S0168-9452(03)00299-1.
  16. ↑ Moorhead, Eric J.; Wenzel, Anna G. (August 2009). "Two Undergraduate Experiments in Organic Polymers: The Preparation of Polyacetylene and Telechelic Polyacetylene via Ring-Opening Metathesis Polymerization". Journal of Chemical Education . 86 (8): 973. Bibcode:2009JChEd..86..973M. doi:10.1021/ed086p973.
  17. ↑ Kunichika, Sango (1953). "Cyclopolyolefins Derived from Acetylene". Bulletin of the Institute for Chemical Research, Kyoto University. 31 (5): 323–335. hdl:2433/75368.
  18. ↑ Holovka, J. M.; Gardner, P. D.; Strow, C. B.; Hill, M. L.; Van Auken, T. V. (1968). "Photolysis and photoisomerization of cyclooctatetraene oxide". Journal of the American Chemical Society. 90 (18): 5041–5043. doi:10.1021/ja01020a058.
  19. ↑ Katz, Thomas J. (1960). "The cyclooctatetraenyl dianion". J. Am. Chem. Soc. 82 (14): 3784–3785. doi:10.1021/ja01499a077.
  20. ↑ "JST Nanostructed Materials Project Highlights – Prof. Nakajima's Presentation". Archived from the original on 2008-02-19. Retrieved 2005-11-24.
  21. ↑ Cotton, F. Albert; Hunter, Douglas L. (1976). "Carbon-13 Nuclear Magnetic Resonance Study of the Fluxional Behavior of Cyclooctatetraenetricarbonyliron and -Ruthenium". Journal of the American Chemical Society. 98 (6): 1413–1417. doi:10.1021/ja00422a022.
  22. ↑ R. Pettit and J. Henery (1970). "cis-dichlorocyclobutene". Organic Syntheses. 50: 36. doi:10.15227/orgsyn.050.0036.
  23. ↑ "CYCLOBUTADIENE IN SYNTHESIS: Endo-TRICYCLO[4.4.0.02,5]DECA-3,8-DIENE-7,10-DIONE". Organic Syntheses. 55: 43. 1976. doi:10.15227/orgsyn.055.0043.
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