10.1.4 Organic Families - Hydrocarbons

• Hydrocarbons are compounds containing hydrogen and carbon only
• There are four families of hydrocarbons you should know: alkanes, alkenes, alkynes and arenes
• Alkanes have the general molecular formula C_nH_2n+2. They contain only single bonds and are said to be saturated
• Alkanes are named using the nomenclature rule alk + ane
• The alk depends on the number of carbons as outlined in the previous Section 10.1.2

The first six members of the alkane family

• Alkenes have the general molecular formula C_nH_2n
• They are said to be unsaturated
• Alkenes are named using the nomenclature rule alk + ene
• In molecules with a straight chain of 4 or more carbon atoms, the position of the C=C double bond must be specified
• The carbon atoms on the straight chain must be numbered, starting with the end closest to the double bond
• The lowest-numbered carbon atom participating in the double bond is indicated just before the -ene:

The first five members of the alkene family

• There is a distinction to be made between the name of the functional group and the name of the family
• The name of the family is alkene, but the name of the functional group is alkenyl

• Alkynes have the general molecular formula C_nH_2n-2
• The triple bond makes them unsaturated molecules
• Alkynes are named using the nomenclature rule alk + yne
• As with alkenes, in molecules with a straight chain of 4 or more carbon atoms, the position of the triple bond must be specified
• The carbon atoms on the straight chain must be numbered, starting with the end closest to the triple bond
• The lowest-numbered carbon atom participating in the triple bond is indicated just before the -yne:

The first five members of the alkyne family

• The name of the functional group is alkynyl

• Arene is the collective name given to compounds with one or more rings with pi electrons that are delocalised throughout the ring(s)
• Compounds with this feature are said to be aromatic
• This doesn't mean they are necessarily smelly, although a lot of naturally occurring arenes do have distinctive smells!

Arenes are present in many everyday chemicals and pharmaceuticals

• Benzene, C₆H₆, is the only aromatic hydrocarbon that is covered in IB Chemistry and is dealt with in Section 10.1.12
• The functional group in benzene is known as a phenyl group when attached to other molecules