1. Structure of aliphatic hydrocarbons

2. Aliphatic hydrocarbons
Aliphatic hydrocarbons are hydrocarbons that consist of straight or branched chains of carbon atoms, or rings of carbon atoms other than those containing a special ring called a benzene ring

3. Pentane – a straight chain aliphatic hydrocarbon

4. A branched chain hydrocarbon

5. Cyclohexane – a cyclic aliphatic hydrocarbon

6. Homologous series
A homologous series is a family of organic compounds with the same general formula, similar chemical properties, and successive members differing by CH2
Alkanes, alkenes and alkynes are three different homologous series of aliphatic hydrocarbons

7. Alkanes
Alkanes are a homologous series of hydrocarbons with the general formula CnH2n+2
They are named systematically, with a prefix indicating the number of carbon atoms per molecule, and the ending “ane”

8. Alkanes Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10
Pentane C5H12
Hexane C6H14
Heptane C7H16
Octane C8H18

9. Alkanes
Alkane molecules are tetrahedral, e.g. propane

10. Structural formulas
The structural formula of an alkane indicates the way atoms in a molecule of the alkane are bonded together
The following slides show the structural formulas of some of the alkanes

11. Methane

12. Ethane

13. Propane

14. Butane

15. Pentane

16. Structural isomers
Structural isomers are compounds that have the same molecular formula but different structural formulas
Butane (C4H10)is the simplest alkane which has structural isomers, called butane and 2-methylpropane respectively
The name 2-methylpropane indicates that there is a methyl (CH3) group attached instead of one of the hydrogen atoms to the second carbon in propane

17. Isomers of butane

18. An isomer of octane (C8H18)
2,2,4-trimethylpentane is so called because there are two methyl groups attached (in place of hydrogen atoms) to the second carbon atom and one (in place of another hydrogen atom) to the fourth carbon atom in a pentane molecule

19. Physical properties of alkanes
Physical state: The first four alkanes are gases, while pentane and higher alkanes are liquids
Insoluble in water
Soluble in non-polar solvents such as cyclohexane

20. Alkenes
Alkenes are a homologous series of hydrocarbons with the general formula CnH2n
They are named systematically, with a prefix indicating the number of carbon atoms per molecule, and the ending “ene”

21. Alkenes
Ethene C2H4
Propene C3H6
But-1-ene C4H8
But-2-ene C4H8

22. Ethene

23. Propene

24. But-1-ene

25. But-2-ene

26. Physical properties of alkenes
Physical state: Gases
Insoluble in water
Soluble in non-polar solvents such as cyclohexane

27. Alkynes
Alkynes are a homologous series of hydrocarbons with the general formula CnH2n-2
Ethyne (C2H2) is the first member of the series

28. Physical properties of ethyne
Physical state: Gas
Insoluble in water
Soluble in non-polar solvents such as cyclohexane