A hydrocarbon is a substance that contains only carbon and hydrogen.
There are three main hydrocarbons on the course – alkanes, alkenes and alkynes.
A homologous series is a series of compounds:
- of similar chemical type.
- that show gradual change in their physical properties.
- all are prepared in a similar way.
- have a common general formula .
- differ one from the next by a group.
The first homologous series we deal with is calles the alkanes (The ending tells us the chemical family).
- Methane –
- Ethane –
- Propane –
- Butane –
- Pentane –
- Hexane –
- Heptane –
- Octane –
- Nonane –
- Decane –
Structural isomers are compounds with the same molecular formula but different structural formulas.
The isomers are named systematically by IUPAC (International UNion of Pure and Applied Chemistry). The above is names as 2, methy propane.
How to give systematic names to Isomers
- Identify the longest straight chain. (eg. propane).
- Identify any groups hanging off the chain. (eg. – methyl).
- Number the carbons to identify (bu the lowest number) which carbon the methyl group is hanging off – (In this case 2).
The name of the compound: 2, methyl propane.
Representing Structures of Organic Molecules
The alkenes are the second homologous series of hydrocarbons in the course.
- Alkenes contain a carbon-carbon double bond
- Alkenes are said to be unsaturated.
- General formula:
- In the lab ethene is made by dehydrating ethanol using the dehydrating agent aluminium oxide.
Alkynes are hydrocarbons characterised by a carbon-carbon triple bond.
- Alkynes contain a carbon-carbon triple bond
- They are highly unsaturated.
- General formula:
- To prepare ethyne, we drop water onto calcium dicarbide or calcium carbide.
Configurations of carbons
When a carbon is surrounded by four single bonds, it is said to be in tetrahedral configuration.
Aromatic compounds are compounds that contain a benzene ring structure in their molecules.
An aliphatic compound is an organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble then in chemical properties.