Cyclopentadiene
| Cyclopentadiene | |
|---|---|
| |
| General | |
| Systematic name | 1,3-cyclopentadiene |
| Other names | cyclopentadien, pentole, pyropentylene |
| Molecular formula | C5H6 |
| SMILES | C1C=CC=CC1 |
| Molar mass | 66.10 g/mol |
| Appearance | colourless liquid |
| CAS number | [542-92-7] |
| Properties | |
| Density and phase | 0.81 g/cm³, liquid |
| Solubility in hexane, benzene, toluene |
miscible |
| Melting point | -85 °C (188 K) |
| Boiling point | 41 °C (314 K) |
| Structure | |
| Molecular shape | envelope structure |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| EU classification | not listed |
| NFPA 704 | |
| Flash point | 25 °C |
| RTECS number | GY1000000 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related hydrocarbon | Benzene Cyclobutadiene |
| Related compounds | Dicyclopentadiene |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references | |
Cyclopentadiene, with molecular formula C5H6, is a clear, colorless, liquid organic chemical, with an odor reminiscent of turpentine or camphor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene through a Diels-Alder reaction. This dimer can be cracked and separated into the monomer by distillation at atmospheric pressure.
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.
Properties
Monomeric cyclopentadiene's methylene hydrogens rapidly undergo [1,5] sigmatropic shifts and occupy positions at all carbons; at room temperature the NMR spectrum appears as a single peak at 4.8 ppm. At lower temperatures, these resolve into peaks at 4.0, 5.2, and 5.4 ppms, which reflect the static structure drawn in most depictions of cyclopentadiene.
The compound is weakly acidic, unusual for a hydrocarbon. This relatively high acidity is caused by the formation of an energetically favourable aromatic, anionic, 5-membered ring (cyclopentadienyl anion, C5H5−, commonly abbreviated as Cp). Deprotonation can easily be achieved, e.g. by alkali metal bases. The anion can act as a weak nucleophile in organic reactions, or combine with a number of different transition metals to form cyclopentadienyl complexes, such as metallocenes.
Reactivity of cyclopentadiene
Cyclopentadiene readily undergoes Diels-Alder reactions with dienophiles.
Deprotonation results in the cyclopentadienyl-anion
Uses
- Reacts with Linseed oil & makes it dry more quickly on contact with oxygen.
- Could be used to accelerate Oil paintings dry time, but it can cost the painting itself & possibly canvas rot.
See also
References
- Girolami, G. S.; Rauchfuss, T. B.; & Angelici, R. J. (1999). Synthesis and Technique in Inorganic Chemistry, A Laboratory Manual (3rd Edn.) Sausalito, CA: University Science Books.
- Streitwieser, A.; Heathcock, C. H.; Kosower, E. M. (1998). Introduction to Organic Chemistry (4th Edn.) Upper Saddle River, NJ: Prentice Hall.
- ChemFinder "Dicyclopentadiene" Accessed 2005-04-13.