Cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−.
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| Names | |||
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| Preferred IUPAC name
Cyclopenta-1,3-diene | |||
| Other names
1,3-Cyclopentadiene Pyropentylene | |||
| Identifiers | |||
3D model (JSmol) |
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| Abbreviations | CPD, HCp | ||
| 471171 | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.008.033 | ||
| EC Number |
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| 1311 | |||
| MeSH | 1,3-cyclopentadiene | ||
PubChem CID |
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| RTECS number |
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| UNII | |||
CompTox Dashboard (EPA) |
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| Properties | |||
| C5H6 | |||
| Molar mass | 66.103 g·mol−1 | ||
| Appearance | Colourless liquid | ||
| Odor | irritating, terpene-like | ||
| Density | 0.802 g cm−3 | ||
| Melting point | −90 °C; −130 °F; 183 K | ||
| Boiling point | 39 to 43 °C; 102 to 109 °F; 312 to 316 K | ||
| insoluble | |||
| Vapor pressure | 400 mmHg (53 kPa) | ||
| Acidity (pKa) | 16 | ||
| Conjugate base | Cyclopentadienyl anion | ||
| −44.5×10−6 cm3 mol−1 | |||
Refractive index (nD) |
1.44 (at 20 °C) | ||
| Structure | |||
| Planar | |||
| 0.419 D | |||
| Thermochemistry | |||
Heat capacity (C) |
115.3 J·mol−1·K−1 | ||
Std molar entropy (S⦵298) |
182.7 J·mol−1·K−1 | ||
Std enthalpy of formation (ΔfH⦵298) |
105.9 kJ·mol−1 | ||
| Hazards | |||
| Flash point | 25 °C (77 °F; 298 K) | ||
| Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration) |
14,182 ppm (rat, 2 hr) 5091 ppm (mouse, 2 hr) | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) |
TWA 75 ppm (200 mg/m3) | ||
REL (Recommended) |
TWA 75 ppm (200 mg/m3) | ||
IDLH (Immediate danger) |
750 ppm | ||
| Related compounds | |||
Related hydrocarbons |
Benzene Cyclobutadiene Cyclopentene | ||
Related compounds |
Dicyclopentadiene | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |||
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 can be restored by heating to give the monomer.
The compound is mainly used for the production of cyclopentene and its derivatives. It is popularly used as a precursor to the cyclopentadienyl anion (Cp−), an important ligand in cyclopentadienyl complexes in organometallic chemistry.
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