Cyclopropene
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| Names | |||
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Systematic IUPAC name
Cyclopropene
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| Identifiers | |||
2781-85-3 
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| 3D model (Jmol) | Interactive image | ||
| ChemSpider |
109788 
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| MeSH | cyclopropene | ||
| PubChem | 123173 | ||
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| Properties | |||
| C3H4 | |||
| Molar mass | 40.07 g·mol−1 | ||
| Boiling point | −36 °C (−33 °F; 237 K) | ||
| Thermochemistry | |||
| 51.9-53.9 J K−1 mol−1 | |||
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Std enthalpy of
combustion (ΔcH |
-2032--2026 kJ mol−1 | ||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is ?) |
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| Infobox references | |||
Cyclopropene is an organic compound with the formula C3H4. It is the simplest cycloalkene. It has a triangular structure. Because the ring is highly strained, cyclopropene is difficult to prepare, and a useful core for studies of bonding and molecular orbitals. The reduced length of the double bond compared to a single bond causes the angle opposite the double bond to narrow to about 51° from the 60° angle found in cyclopropane. As with cyclopropane, the carbon–carbon bonding in the ring has increased p character: the alkene carbons use sp2.68hybridization for the ring.
The first confirmed synthesis of cyclopropene, carried out by Dem'yanov and Doyarenko, involved the thermal decomposition of trimethylcyclopropylammonium hydroxide over platinized clay at 320–330 °C under a CO2 atmosphere. This reaction produces mainly trimethylamine and dimethylcyclopropyl amine, together with about 5% of cyclopropene. Cyclopropene can also be obtained in about 1% yield by thermolysis of the adduct of cycloheptatriene and dimethyl acetylenedicarboxylate.
Allyl chloride undergoes dehydrohalogenation upon treatment with the base sodium amide at 80 °C to produce cyclopropene in about 10% yield.
The major byproduct of the reaction is allylamine. Adding allyl chloride to sodium bis(trimethylsilyl)amide in boiling toluene over a period of 45–60 minutes produces the targeted compound in about 40% yield with an improvement in purity:
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