Cyclopentadiene: Difference between revisions
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| OtherNames = pentole, pyropentylene, CPD, CpH |
| OtherNames = pentole, pyropentylene, CPD, CpH |
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| Section1 = {{Chembox Identifiers |
| Section1 = {{Chembox Identifiers |
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| SMILES = |
| SMILES = C\1=C\C=C/C/1 |
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| ChemSpiderID = 7330 |
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| InChI = 1/C5H6/c1-2-4-5-3-1/h1-4H,5H2 |
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| InChIKey = ZSWFCLXCOIISFI-UHFFFAOYAI |
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| CASNo_Ref = {{cascite}} |
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| CASNo = 542-92-7 |
| CASNo = 542-92-7 |
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| RTECS = GY1000000 |
| RTECS = GY1000000 |
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Revision as of 15:27, 27 January 2010
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| Names | |||
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| Other names
pentole, pyropentylene, CPD, CpH
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| Identifiers | |||
3D model (JSmol)
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| ChemSpider | |||
| ECHA InfoCard | 100.008.033 | ||
| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |||
| C5H6 | |||
| Molar mass | 66.10 g/mol | ||
| Appearance | colourless liquid | ||
| Density | 0.786 g/cm³, liquid | ||
| Melting point | -85 °C (188 K) | ||
| Boiling point | 41 °C (314 K) | ||
| Insoluble | |||
| Structure | |||
| Planar[1] | |||
| Hazards | |||
| Flash point | 25 °C | ||
| Related compounds | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cyclopentadiene is a organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels-Alder reaction. This dimer "cracks" to give the monomer upon heating.
The compound is the precursor to the popular cyclopentadienyl-ligand ('Cp') in cyclopentadienyl complexes in organometallic chemistry. Both cyclopentadiene and dicyclopentadiene can serve as ligands as well, but such complexes are uncommon.
Production and reactions
Cyclopentadiene production is usually not distinguished from dicyclopentadiene since they are interconverted. They are obtained from coal tar (about 10 – 20 g/ton) and steam cracking from naphtha (about 14 kg/ton).[2]
Sigmatropic rearrangement
The hydrogen atoms in cyclopentadiene undergo rapid [1,5]-sigmatropic shifts as indicated by the variable temperature1H NMR spectra recorded at various temperatures.[3]
Diels-Alder reactions
Famously, cyclopentadiene dimerizes via a reversible Diels-Alder reaction. The rate is convenient at room temperature, and the monomer can be stored for days at -20 °C.[2]
| Relative rate of dimerization of C5H6 | Temperature °C |
|---|---|
| 0.05 | _20 |
| 0.5 | 0 |
| 3.5 | 25 |
| 15 | 40 |
Cyclopentadiene readily undergoes other Diels-Alder reactions with dienophiles, such as 1,4-benzoquinone.[4] Cycloaddition of O2 gives the bicyclic peroxide.
Deprotonation
The compound is acidic with pKa = 16, which is unusual for a hydrocarbon. This relatively high acidity (and low pKa) is explained by the stability of the aromatic, anionic, 5-membered ring (cyclopentadienyl anion, C5H5−). Derivatives of this anion are often depicted as salts, although the free anion does not exist in any appreciable extent in solution.[citation needed] Deprotonation can be achieved, e.g. by alkali metal bases. Sodium cyclopentadienide is commercially available. The anion serves as a weak nucleophile in organic synthesis and combines with numerous anhydrous halides of the transition metals to form cyclopentadienyl complexes, such as metallocenes.[5]
Uses
Cyclopentadiene is a versatile synthetic intermediate, often used to prepare monomers that modify the production of polyolefins. Cyclopentadiene reacts with linseed oil to facilitate "drying" upon contact with oxygen.
See also
- Aromaticity
- Methylcyclopentadiene and pentamethylcyclopentadiene, also found as ligands in organometallic chemistry
References
- ^ Valery I. Faustov, Mikhail P. Egorov, Oleg M. Nefedov and Yuri N. Molin (2000). "Ab initio G2 and DFT calculations on electron affinity of
cyclopentadiene, silole, germole and their 2,3,4,5-tetraphenyl substituted analogs : structure, stability and EPR parameters of the radical anions". Phys. Chem. Chem. Phys. 2: 4293–4297. doi:10.1039/b005247g.
{{cite journal}}: line feed character in|title=at position 58 (help)CS1 maint: multiple names: authors list (link) - ^ a b Dieter Hönicke, Ringo Födisch, Peter Claus, Michael Olson “Cyclopentadiene and Cyclopentene” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_227
- ^ Streitwieser, A.; Heathcock, C. H.; Kosower, E. M. (1998). Introduction to Organic Chemistry (4th Edn.) Upper Saddle River, NJ: Prentice Hall.
- ^ Masaji Oda, Takeshi Kawase, Tomoaki Okada, and Tetsuya Enomoto (1998). "2-Cyclohexene-1,4-dione". Organic Syntheses
{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 9, p. 186. - ^ Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999.ISBN 0935702482