Beginner Topic 734 of 1102 Organic Chemistry
Alkanes
Saturated hydrocarbons with only single bonds and the formula CnH2n+2.
In-depth explanation of Alkanes
Alkanes are saturated hydrocarbons containing only carbon-carbon and carbon-hydrogen single bonds, with the general formula CnH2n+2. Each carbon is sp3 hybridized and the molecules are nonpolar, so they dissolve in nonpolar solvents and are insoluble in water. Their bonds are strong and have low polarity, which makes them fairly unreactive, the main exceptions being combustion and free radical halogenation under light. Boiling points increase with chain length because dispersion forces grow, and branching lowers the boiling point because the molecules pack less closely.
Going deeper: Alkanes
Key ideas: Alkanes are saturated sp3 hydrocarbons CnH2n+2 with only sigma bonds. Boiling point rises with chain length and falls with branching (n-pentane 36 C, isopentane 28 C, neopentane 9.5 C). Characteristic reactions are combustion and free radical halogenation; radical reactivity of C-H is tertiary > secondary > primary. Wurtz reaction doubles the alkyl chain; soda lime decarboxylation gives an alkane with one fewer carbon.
Common mistakes and connections: Students call alkanes completely unreactive; they burn and halogenate readily under light. Another error is assuming branching always lowers the melting point, when symmetrical molecules pack well (neopentane melts higher than n-pentane). Links to petroleum, conformations and radical mechanisms.
Visualization of Alkanes
Boiling points of the straight-chain alkanes climb steadily with chain length as London dispersion forces strengthen. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Propane and butane are common fuels, used in cylinders for cooking and heating.
Frequently asked questions about Alkanes
What is Alkanes?
Saturated hydrocarbons with only single bonds and the formula CnH2n+2.
Is Alkanes a beginner, intermediate or advanced topic?
Alkanes is a beginner topic in Organic Chemistry. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Alkanes?
Study these earlier topics in Organic Chemistry first: Catenation, Functional Groups, Homologous Series.
What comes after Alkanes?
The next topics in Organic Chemistry are Alkenes and Alkynes.
Can I practise Alkanes with quizzes?
Yes. The interactive lesson includes a self-check question on Alkanes, and the Organic Chemistry quiz draws on every topic in this area.
Where Alkanes fits in Organic Chemistry
Alkanes is topic 6 of 148 in Organic Chemistry.