Propalene

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| ImageFile = Propalene.png

| ImageFile1 = Propalene-3D.png

| PIN = Bicyclo[1.1.0]buta-1,3-diene

| OtherNames = Propalene, Bicyclobutadiene

|Section1={{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|??}}

| CASNo = 13969-14-7

| PubChem = 20577920

| SMILES = C1=C2C1=C2

| InChI = 1S/C4H2/c1-3-2-4(1)3/h1-2H

| InChIKey = QYGHRDRLUMAIGS-UHFFFAOYSA-N

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| ChEBI =

| ChemSpiderID_Ref =

| ChemSpiderID = 35806075

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|Section2={{Chembox Properties

| C=4|H=2

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Propalene or bicyclo[1.1.0]buta-1,3-diene is a polycyclic hydrocarbon composed of two fused cyclopropene rings.{{cite journal |title= The nonsinglet instabilities of the hartree-fock solutions for nonalternant hydrocarbons |first1= Azumao |last1= Toyota |first2= Takeshi |last2= Nakajima |journal= Theoretica Chimica Acta |year= 1979 |volume= 53 |issue= 4 |pages= 297–308 |doi= 10.1007/BF00555689 }}{{cite journal |title= cycloButadiene and some other pseudoaromatic compounds |author= D. P. Craig |journal= J. Chem. Soc. |year= 1951 |pages= 3175–3182 |doi= 10.1039/JR9510003175 }} Computational studies indicate that the molecule is planar, with the carbon framework forming a parallelogram that has distinctly alternating short and long carbon–carbon bonds.{{cite journal |title= Numerical Estimation of the Pseudo-Jahn–Teller Effect Using Nonadiabatic Coupling Integrals in Monocyclic and Bicyclic Conjugated Molecules |first1= Shiro |last1= Koseki |first2= Azumao |last2= Toyota |first3= Takasi |last3= Muramatsu |first4= Toshio |last4= Asada |first5= Nikita |last5= Matsunaga |journal= Journal of Physical Chemistry A |year= 2016 |volume= 120 |issue= 51 |pages= 10207–10215 |doi= 10.1021/acs.jpca.6b09632 |bibcode= 2016JPCA..12010207K }}