Ethene, C2H4

Ethene C2H4, formerly called ethylene, has a typical C=C double bond in a flat molecule.

C2H4 molecule model as a ball & stick model and as a more common structure drawing. Every carbon atom is directly bonded to two hydrogen atoms. In between the carbon atoms there is a double bond which is around 1.3 Å long, 1 Å is 1*10-10 m (the Ångstrom unit).


C2H4 is a colorless gas with a slightly sweet smell. The vapor can cause tiredness or dizzyness and gives a high risk for suffocation. Ethene is very flammable and could easily be ignited by sparks. Ethene is wellknown for its ability to stimulate ripening of fruits. In nature the gas is produced during plant metabolism and it´s classified as a plant hormone. Also it´s used in chemical factories for producing plastics such polyethene (polyethylene) and polyvinyl chloride (PVC).


IR of spectrum ethene, C2H4

The IR spectrum of ethene is rather uncomplicated due to its simple structure. It has a strong band at 900 cm-1 (11 µm) due to H-C-H out- of-plane wagging. Also, ethene has relatively weak absorption peaks at 1400 cm-1 (7.1 µm) from H-C-H scissoring and 3100 cm-1 (3.2 µm) from C-H assymetric stretching. Note that the C=C double bond in the C2H4 molecule cannot absorb IR radiation, because it has a totally symmetric vibration. Such a bond is called IR inactive.

Theoretical IR absorption spectrum of ethene, C2H4, from Spectracalc at