Traditionally, the term hydrocarbons has been used to represent compounds derived from petroleum distillation, and hence were considered synonymous with petroleum distillates. But this is incorrect since the term should (logically) cover all organic compounds made of predominantly carbon and hydrogen molecules. The number of carbon molecules can vary from 1 to 60. In general, compounds which contain 1 to 4 carbon molecules are gaseous, while those which have 5 to 19 are liquids, and compounds with more than 20 are solids.
These comprise compounds with saturated molecules (containing no carbon-carbon double or triple bonds) which have straight or branched-chain arrangements. Common examples include butane, ethane, methane, and propane (gaseous) ; benzine, gasoline or petrol, diesel oil, kerosene, mineral seal oil, lubricating oil or mineral oil, and turpentine or pine oil (liquids) ; paraffin wax, petro-leum jelly or vaseline, grease, tar, and asphalt (semi-liquids or solids).
They contain at least one benzene ring and are unsaturated compounds. Common examples include benzene, toluene, xylene, styrene and naphthalene.
Most of these are clear, colourless liquids which have a chloroform-like odour. Common examples include carbon tetrachloride, ethylene dibromide, ethylene dichloride, dichloroethylene, trichloroethylene, methylene chloride, propylene chloride, chloroform, methyl chloroform, methyl bromide, fluorocarbons and organochlorine insec-ticides.
They are saturated hydrogen compounds which are arranged in closed rings. Common examples include cyclohexane and methylcyclopentane.
These compounds contain one carbon-carbon double bond in the molecule. They are mostly used in the manufacture of other hydrocarbon products such as halogenated hydro-carbons.