Alkene

Not to be confused with Alkane or Alkyne.

Distincton of Alkanes and Alkenes. On the left: Cyclohexane does not react with water bromide On the right: Cyclohexene does.

In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond. The simplest alkenes, with only one double bond, no rings, and no other functional groups, are hydrocarbons with the general formula C_nH_2n.

Aromatic compounds are often drawn as cyclic alkenes, but their structure and properties are different and they are not considered to be alkenes.

The double bond in the middle makes them more reactive because the molecule is not saturated. An alkene's unsaturation means that it will take the color out of bromine. The names of alkenes always end with -ene.

List of Alkenes

The following is a list of the first 10 alkenes:

• Ethene (C₂H₄)

• Propene (C₃H₆)
• Butene (C₄H₈)
• Pentene (C₅H₁₀)
• Hexene (C₆H₁₂)
• Heptene (C₇H₁₄)
• Octene (C₈H₁₆)
• Nonene (C₉H₁₈)
• Decene (C₁₀H₂₀)
• Undecene (C₁₁H₂₂)

Physical properties

The physical properties of alkenes are comparable with those of alkanes. The main differences between the two are that the acidity levels of alkenes are much higher than the ones in alkanes. The physical state depends on molecular mass (gases from ethene to butene - liquids from pentene onwards). The simplest alkenes, ethene, propene and butene are gases. Linear alkenes of approximately five to sixteen carbons are liquids, and higher alkenes are waxy solids.

Fuel

Alkenes are not used as fuels because:

1. They are scarce in nature. They are made from other hydrocarbons to make plastics, anti–freeze and many other useful compounds.
2. They burn with a smoky flame due to less efficient, and more polluting incomplete combustion, so the heat energy release is lower than for alkanes.