Alkenes Alkenes: hydrocarbons that contain a carbon–carbon double bond. Use the same prefix as for alkane but follow by “-ene” General formula: C n H 2n CH 2 =CH 2 ethene CH 3 CH 2 =CH 2 propene

Alkenes C 4 H 8 is butene and the placement of the double bond must be indicated with the lowest number. CH 3 CH 2 CH=CH 2 1-butene CH 3 CH=CHCH 3 2-butene CH 2 =CHCH 2 CH 3 Still 1-butene!

Cis-Trans Isomerism Alkenes exhibit cis-trans isomerism depending on whether the alkyl groups connected to the carbons with the double bond are on the same side of the double bond (cis) or on opposite sides of the double bond (trans). This is because, unlike single bonds, double bonds are rigid and are unable to rotate.

Example: cis-2-butene trans-2-butene

Example: Cis-Trans Isomerism 1-butene: Note that cis-trans isomerism is not possible with 1-butene because there is only one alkyl group connected to a carbon with the double bond.

Alkynes Alkynes: contain a triple bond and have the general formula C n H 2n-2 Use the same prefixes as for alkane but follow by “-yne” HC ≡ CH ethyne (acetylene) HC ≡ CCH 3 propyne Just like with alkenes the placement of the triple bond must be indicated with a number.

Name the following alkyne: Example: Parent name? 3-heptyne5-ethyl- Substituents?

Name the following: Example: Parent name? 2-hexenetrans-4-methyl- Substituents?

Aromatic Hydrocarbons Aromatic hydrocarbons are cyclic unsaturated (contain multiple bonds) hydrocarbons. The most important aromatic hydrocarbon is benzene, C 6 H 6 (an important non-polar solvent).

Benzene Benzene can be drawn in different ways: Or summarized as:

Substituents on Aromatic Hydrocarbons When substituents are added to benzene rings you can use the naming rules previously mentioned, or use: ortho (o) for substituents on the 1,2 carbons meta (m) for substituents on the 1,3 carbons para (p) for substituents on the 1,4 carbons

Name the following: Example: Parent name? benzene1-ethyl-4-methyl Substituents? para-ethylmethylbenzene p-ethylmethylbenzene