methylacetylene (propyne). C3H4 -> H3CC#CH Attempted fractional distillation of cyclopropene at –36 °C (its predicted boiling point) results in polymerization. The mechanism is assumed to be a free-radical chain reaction, and the product, based on NMR spectra, is thought to be polycyclopropane. Cyclopropene undergoes the Diels–Alder reaction with cyclopentadiene to give endo-tricyclo[3.2.1.02,4]oct-6-ene. This reaction is commonly used to check for the presence of cyclopropene, following its synthesis. Related compounds Malvalic acid is a toxic cyclopropene fatty acid that occurs in cottonseed oil. 1-Methylcyclopropene (1-MCP) is used to slow the ripening in fruits. Borirenes, phosphirenes, and silirenes are boron-, phosphorus-, and silicon-substituted cyclopropenes, with the formula , and . Cyclopropene fatty acids a class of naturally occurring cyclopropenes. References External links Cycloalkenes Gases Annulenes