Editing Cyclopentadiene (section)

===Diels–Alder reactions===
Cyclopentadiene is a highly reactive [[diene]] in the [[Diels–Alder reaction]] because minimal distortion of the diene is required to achieve the envelope geometry of the transition state compared to other dienes.<ref>{{cite journal |first1=Brian |last1=Levandowski |first2=Ken |last2=Houk |date=2015 |title=Theoretical Analysis of Reactivity Patterns in Diels–Alder Reactions of Cyclopentadiene, Cyclohexadiene, and Cycloheptadiene with Symmetrical and Unsymmetrical Dienophiles |doi=10.1021/acs.joc.5b00174 |pmid=25741891 |journal=[[J. Org. Chem.]] |volume=80 |issue=7 |pages=3530–3537}}</ref> Famously, cyclopentadiene dimerizes. The conversion occurs in hours at room temperature, but the monomer can be stored for days at −20&nbsp;°C.<ref name=Ullmann>{{Ullmann|first1=Dieter |last1=Hönicke |first2=Ringo |last2=Födisch |first3=Peter |last3=Claus |first4=Michael |last4=Olson |title=Cyclopentadiene and Cyclopentene |DOI=10.1002/14356007.a08_227}}</ref>