The molecule was found in an interstellar cloud of dust and gas near the centre of the Milky Way Galaxy by radio astronomers using the National Science Foundation's 12 Meter Telescope at Kitt Peak, Arizona.
"The discovery of vinyl alcohol is significant," said Barry Turner from the US National Radio Astronomy Observatory, "because it gives us an important tool for understanding the formation of complex organic compounds in interstellar space".
"It may also help us better understand how life might arise elsewhere in the Cosmos."
Mr Turner made the discovery with A. J. Apponi of the University of Arizona's Steward Observatory in Tucson.
Vinyl alcohol is an important intermediary in many organic chemical reactions on Earth. There are three stable members of the C2H4O group of isomers. Vinyl alcohol is the last of the three to be found in interstellar space.
Isomers are molecules with the same atoms, but in different arrangements.
It is thought that most of the molecules detected in space are formed by gas-phase chemistry, where small molecules (and occasionally atoms) manage to "lock horns" when they collide in space.
But this process cannot explain how vinyl alcohol and other complex chemicals are formed in detectable amounts. The question is how building blocks for vinyl alcohol and other chemicals form the necessary chemical bonds to make larger molecules - those containing six or more atoms.
"It has been an ongoing quest to understand exactly how these more complex molecules form and become distributed throughout the interstellar medium," said Mr Turner.
The researchers found the vinyl alcohol in Sagittarius B - a massive molecular cloud located some 26,000 light-years from Earth.
Turner and others speculate that since the cloud lies near an area of young, energetic star formation, the energy from these stars could evaporate the icy surface layers of the microscopic dust grains in interstellar clouds, which is where molecules are thought to form.
This evaporation would liberate the molecules, depositing them into interstellar space where they can be detected by sensitive radio antennas on Earth.
The astronomers were able to detect the specific radio signature of vinyl alcohol using 2- and 3-mm band radio frequencies during the observational period of May and June this year.