Hydrocarbons

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic; their odor is usually faint, and may be similar to that of gasoline or lighter fluid. They occur in a diverse range of molecular structures and phases: they can be gases (such as methane and propane), liquids (such as hexane and benzene), low melting solids (such as paraffin wax and naphthalene) or polymers (such as polyethylene and polystyrene). In the fossil fuel industries, hydrocarbon refers to naturally occurring petroleum, natural gas and coal, or their hydrocarbon derivatives and purified forms. Combustion of hydrocarbons is the main source of the world's energy. Petroleum is the dominant raw-material source for organic commodity chemicals such as solvents and polymers. Most anthropogenic (human-generated) emissions of greenhouse gases are either carbon dioxide released by the burning of fossil fuels, or methane released from the handling of natural gas or from agriculture. As defined by the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry, hydrocarbons are classified as follows: Saturated hydrocarbons, which are the simplest of the hydrocarbon types. They are composed entirely of single bonds and are saturated with hydrogen. The formula for acyclic saturated hydrocarbons (i.e., alkanes) is C_nH_2n+2. The most general form of saturated hydrocarbons, (whether linear or branched species, and whether with without one or more rings) is C_nH_2n+2(1-r), where r is the number of rings. Those with exactly one ring are the cycloalkanes. Saturated hydrocarbons are the basis of petroleum fuels and may be either linear or branched species. One or more of the hydrogen atoms can be replaced with other atoms, for example chlorine or another halogen: this is called a substitution reaction. An example is the conversion of methane to chloroform using a chlorination reaction.