Study Chemistry notes on Alkenes from Hamilton High School. Useful for tertiary revision, coursework support, and exam preparation in Zimbabwe.
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HAMILTON HIGH SCHOOL SCIENCE DEPARTMENT
"ORGANIC CHEMISTRY-ALKENES" COMPILED BY C CHAKWANA
Alkenes are a family of hydrocarbons (compounds containing carbon and hydrogen only) containing a carbon-carbon double bond. Eg the first two are:
ethene | $\mathrm{C}_{2} \mathrm{H}_{4}$
propene | $\mathrm{C}_{3} \mathrm{H}_{6}$
They are a homologous series with a general formula: $\mathbf{C}_{\mathbf{n}} \mathbf{H}_{\mathbf{2 n}}$
Boiling Points
The boiling point of each alkene is very similar to that of the alkane with the same number of carbon atoms. Ethene, propene and the various butenes are gases at room temperature. All the rest that you are likely to come across are liquids.
In each case, the alkene has a boiling point which is a small number of degrees lower than the corresponding alkane. The only attractions involved are Van der Waals dispersion forces, and these depend on the shape of the molecule and the number of electrons it contains. Each alkene has 2 fewer electrons than the alkane with the same number of carbons.
Naming of alkenes
-Alkenes are generally named using the prefix that denotes the number of carbons and the suffix: -ene that denotes that they are alkenes Many of the same rules for alkanes apply to alkenes
1. Name the parent hydrocarbon by locating the longest carbon chain that contains the double bond and name it according to the number of carbons with the suffix -ene.
Parent = pentene
not hexene
(does not contain double bond)
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