| Cyclopentadiene | |
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| Other names | pentole, pyropentylene, CPD |
| Identifiers | |
| CAS number | 542-92-7  |
| RTECS number | GY1000000 |
| SMILES |
C1C=CC=C1
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| Properties | |
| Molecular formula | C5H6 |
| Molar mass | 66.10 g/mol |
| Appearance | colourless liquid |
| Density | 0.81 g/cm³, liquid |
| Melting point |
-85 °C (188 K) |
| Boiling point |
41 °C (314 K) |
| Solubility in water | Insoluble |
| Structure | |
| Molecular shape | Planar[1] |
| Hazards | |
| Flash point | 25 °C |
| Related compounds | |
| Related hydrocarbon | Benzene Cyclobutadiene Cyclopentene |
| Related compounds | Dicyclopentadiene |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Cyclopentadiene is a chemical compound with the formula C5H6. This colorless liquid organic chemical 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 these are uncommon.
Contents |
Properties
The hydrogen atoms in cyclopentadiene undergo rapid [1,5]-sigmatropic shifts as indicated by the variable temperature1H NMR spectra recorded at various temperatures.[2]
Reactivity of cyclopentadiene
Cyclopentadiene readily undergoes Diels-Alder reactions with dienophiles, such as 1,4-benzoquinone.[3]
The compound is acidic with pKa=16, which is unusual for a hydrocarbon. This relatively high acidity 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.[4]
Uses
Aside from its use as a synthetic intermediate, cyclopentadiene itself has few applications because it reverts so readily to dicyclopentadiene. 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:.
- ^ 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", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv9p0186; Coll. Vol. 9: 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
External links
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