a colourless, flammable, nontoxic, chemically stable gas belonging to the family of organohalogen compounds (organohalogen compound) and used as the starting material in making polyvinyl fluoride, a plastic used in films for weather-resistant coatings of structural materials. Vinyl fluoride is prepared from acetylene and hydrogen fluoride by direct reaction in the presence of HgCl₂ or by first treating acetylene with excess hydrogen fluoride to form CH₃CHF₂, which is then converted to H₂C=CHF by heating at 700 °C (1,300 °F). Vinyl fluoride is also prepared by the reaction of vinyl chloride with hydrogen fluoride to give 1-chloro-1-fluoroethane, followed by dehydrochlorination at 500–600 °C (930–1,100 °F).