In organic chemistry, the suffix -ene tells you a molecule contains a carbon-carbon double bond (C=C). It replaces the -ane ending of the matching alkane, so ethane becomes ethene, marking the compound as an unsaturated alkene.
The -ene suffix is the naming tag for a carbon-carbon double bond (). When you see it at the end of a name, you know the molecule is an alkene, an unsaturated hydrocarbon. You build the name by finding the longest carbon chain that passes through the double bond, then swapping the alkane's -ane ending for -ene: ethane → ethene, propane → propene, butane → butene.
A number usually sits in front of the suffix to show where the double bond starts, like but-2-ene, meaning the C=C begins at carbon 2. That number matters because the same molecular formula can give different molecules depending on where the double bond lives. The -ene also signals reactivity: that double bond is an electron-rich site that loves addition reactions, which is a big reason alkenes behave so differently from their saturated alkane cousins.
The -ene suffix shows up in two places you'll lean on all course long. In Topic 3.1 (Functional Groups), the C=C is one of the first functional groups you learn to spot, because it changes how a molecule dissolves and reacts. In Topic 7.3 (Naming Alkenes), the suffix is the core of the nomenclature rules, where you practice locating the parent chain through the double bond and assigning the lowest possible locant number. Getting comfortable with -ene early pays off when you reach alkene reaction mechanisms, since you can't track what's happening to a double bond if you can't name where it is.
Keep studying Organic Chemistry Unit 7
Visual cheatsheet
view galleryAlkene (Units 3, 7)
Any compound whose name ends in -ene is an alkene by definition. The suffix is literally how you label the whole class of molecules built around a C=C double bond.
Unsaturated (Unit 3)
The -ene ending means the molecule is unsaturated, meaning it has fewer hydrogens than the equivalent alkane because two carbons share a double bond instead of single bonds to extra H atoms.
Addition Reaction (Unit 7)
The double bond that -ene signals is exactly what gets attacked in addition reactions. Knowing a molecule is an -ene tells you it can add HBr, H2, or water across that C=C.
Alkyne (Unit 7)
Swap -ene for -yne and you've gone from a double bond to a triple bond. The two suffixes work the same way structurally, so learning -ene sets you up to read -yne names instantly.
Expect -ene to come up in naming problems and structure-drawing questions. On problem sets and quizzes you'll be handed a structure and asked to name it (assign the parent chain through the double bond, give the locant, finish with -ene) or given a name like 3-methylpent-2-ene and asked to draw it. In reaction questions, spotting the -ene tells you the molecule has a reactive double bond, which is your cue to predict an addition product. A common point loss is putting the locant in the wrong spot or forgetting that the parent chain must include the C=C even when a longer chain exists elsewhere.
-ene means a carbon-carbon double bond (C=C), while -yne means a carbon-carbon triple bond (C≡C). Ethene has a double bond; ethyne (acetylene) has a triple bond. The suffixes look similar, so check whether the molecule has two or three bonds between those carbons before you name it.
The -ene suffix means the molecule contains at least one carbon-carbon double bond and is an alkene.
You name an alkene by replacing the alkane's -ane ending with -ene, so ethane becomes ethene and propane becomes propene.
A number in front of -ene shows where the double bond starts, like but-2-ene meaning the C=C begins at carbon 2.
The parent chain must pass through the double bond, even if a longer chain exists somewhere else in the molecule.
The double bond marked by -ene makes alkenes unsaturated and reactive, especially toward addition reactions.
It means the molecule has a carbon-carbon double bond (C=C) and belongs to the alkene family. You get the name by replacing the matching alkane's -ane ending with -ene, like turning butane into butene.
Not always. One double bond gives -ene, but two gives -diene and three gives -triene (as in buta-1,3-diene). The suffix tells you there's a C=C present, and prefixes like di- or tri- tell you how many.
-ene means a carbon-carbon double bond (C=C) and names an alkene, while -yne means a carbon-carbon triple bond (C≡C) and names an alkyne. Ethene has a double bond; ethyne has a triple bond.
The number is the locant, and it tells you which carbon the double bond starts on. In pent-2-ene the C=C begins at carbon 2, and you always number the chain to give the double bond the lowest possible locant.
The C=C double bond is an electron-rich site that attracts reagents, so alkenes readily undergo addition reactions. Alkanes only have single bonds, so they're much less reactive by comparison.