Editing Cyclopentadiene (section)

{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 448739996
| ImageFileL1 = Cyclopentadiene.png
| ImageNameL1 = Skeletal formula of cyclopentadiene
| ImageFileR1 = Cyclopentadiene-3D-vdW.png
| ImageNameR1 = Spacefill model of cyclopentadiene
| ImageFile2 = Cyclopentadiene-3D-balls.png
| ImageSize2 = 100
| ImageName2 = Ball and stick model of cyclopentadiene
| PIN = Cyclopenta-1,3-diene
| OtherNames = 1,3-Cyclopentadiene<ref name=PGCH/><br />Pyropentylene<ref>{{cite book |author = William M. Haynes |title = CRC Handbook of Chemistry and Physics |publisher = CRC Press/Taylor and Francis |date = 2016 |isbn = 978-1498754286 |volume=97 |page=276 (3-138) |trans-title=Physical Constants of Organic Compounds}}</ref>
|Section1={{Chembox Identifiers
| Abbreviations = CPD, HCp
| CASNo = 542-92-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 7612
| ChemSpiderID = 7330
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII = 5DFH9434HF
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 208-835-4
| MeSHName = 1,3-cyclopentadiene
| ChEBI = 30664
| ChEBI_Ref = {{ebicite|correct|EBI}}
| RTECS = GY1000000
| Beilstein = 471171
| Gmelin = 1311
| SMILES = C1C=CC=C1
| StdInChI = 1S/C5H6/c1-2-4-5-3-1/h1-4H,5H2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/C5H6/c1-2-4-5-3-1/h1-4H,5H2
| StdInChIKey = ZSWFCLXCOIISFI-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = ZSWFCLXCOIISFI-UHFFFAOYAI
}}
|Section2={{Chembox Properties
| C = 5
| H = 6
| Appearance = Colourless liquid
| Odor = irritating, [[terpene]]-like<ref name=PGCH/>
| Density = 0.802 g/cm<sup>3</sup>
| MeltingPtK = 183
| BoilingPtK = 312 to 316
| pKa = 16
| ConjugateBase = [[Cyclopentadienyl anion]]
| Solubility = insoluble<ref name=PGCH/>
| VaporPressure = {{convert|400|mmHg|kPa|abbr=on}}<ref name=PGCH/>
| RefractIndex = 1.44 (at 20&nbsp;°C)<ref name="CRC97">{{Cite book |url=https://www.worldcat.org/oclc/930681942 |title=CRC handbook of chemistry and physics : a ready-reference book of chemical and physical data. |date=2016 |editor1=William M. Haynes |editor2=David R. Lide |editor3=Thomas J. Bruno |isbn=978-1-4987-5428-6 |edition=2016-2017, 97th |location=Boca Raton, Florida |publisher=CRC Press |oclc=930681942}}</ref>
| MagSus = {{val|-44.5e-6|u=cm<sup>3</sup>/mol}}
}}
|Section3={{Chembox Structure
| MolShape = Planar<ref>{{cite journal | title = 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 | first1= Valery I. |last1=Faustov |first2=Mikhail P. |last2=Egorov |first3=Oleg M. |last3=Nefedov |first4=Yuri N. |last4=Molin | journal = Phys. Chem. Chem. Phys. | year = 2000 | volume = 2 | pages = 4293–4297 | doi = 10.1039/b005247g | issue = 19| bibcode= 2000PCCP....2.4293F }}</ref>
| Dipole = 0.419 [[Debye|D]]<ref name="CRC97"/>
}}
|Section4={{Chembox Thermochemistry
| Entropy = 182.7&nbsp;J/(mol·K)
| HeatCapacity = 115.3&nbsp;J/(mol·K)
| DeltaHform = 105.9&nbsp;kJ/mol<ref name="CRC97"/>
}}
|Section5={{Chembox Hazards
| FlashPtC = 25
| PEL = TWA 75 ppm (200&nbsp;mg/m<sup>3</sup>)<ref name=PGCH>{{PGCH|0170}}</ref>
| IDLH = 750 ppm<ref name=PGCH/>
| REL = TWA 75 ppm (200&nbsp;mg/m<sup>3</sup>)<ref name=PGCH/>
| LC50 = 14,182 ppm (rat, 2&nbsp;[[hour|h]])<br/>5091 ppm (mouse, 2&nbsp;h)<ref>{{IDLH|542927|Cyclopentadiene}}</ref>
| AutoignitionPtC = 640
| NFPA-H = 2
| NFPA-F = 3
| NFPA-I = 0
}}
|Section6={{Chembox Related
| OtherFunction_label = [[hydrocarbon]]s
| OtherFunction = [[Benzene]]<br/>[[Cyclobutadiene]]<br/>[[Cyclopentene]]
| OtherCompounds = [[Dicyclopentadiene]]
}}
}}

'''Cyclopentadiene''' is an [[organic compound]] with the [[chemical formula|formula]] C<sub>5</sub>H<sub>6</sub>.<ref name=scha1965>LeRoy H. Scharpen and Victor W. Laurie (1965): "Structure of cyclopentadiene". ''The Journal of Chemical Physics'', volume 43, issue 8, pages 2765–2766. {{doi|10.1063/1.1697207}}.</ref> It is often abbreviated '''CpH''' because the [[cyclopentadienyl anion]] is abbreviated Cp<sup>&minus;</sup>.

This colorless liquid has a strong and [[unpleasant odor]]. At room temperature, this cyclic [[diene]] [[dimer (chemistry)|dimerizes]] over the course of hours to give [[dicyclopentadiene]] via a [[Diels–Alder reaction]]. This dimer can be [[retro-Diels–Alder reaction|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<sup>&minus;</sup>), an important [[ligand]] in [[cyclopentadienyl complex]]es in [[organometallic chemistry]].<ref>{{cite book |last=Hartwig |first= J. F. |title=Organotransition Metal Chemistry: From Bonding to Catalysis |publisher=University Science Books |location=New York, NY |date=2010 |isbn=978-1-891389-53-5}}</ref>