methane and its homologues are called limit (saturated) paraffinic hydrocarbons or alkanes.The last-named organic substances (have the general chemical formula CnH2n + 2, which reflects the saturation of the molecules, atoms that are related by simple covalent carbon-hydrogen bonds or carbon-carbon) are given in accordance with the International Nomenclature of chemical compounds.They have two main sources: crude oil and natural gas.Properties in the homologous series of alkanes with an increase in the number of carbon atoms of the molecule are changed regularly.
first four members of the homologous series have historically name.Hydrocarbons, behind them are denoted by the Greek numerals ending -en.The relative molecular weight of each subsequent hydrocarbon different from the previous 14 amuPhysical properties of alkanes, such as melting point (solidification) and boiling (condensation), the density and the refractive index increase with increasing molecular weight.With methane butane - gases with pentane at pentadecane-liquid, followed by the solids.All paraffins lighter than water and does not dissolve in it.By alkanes include:
- CH4 - methane;
- C2H6 - ethane;
- C3H8 - propane;
- C4H10 - butane;
- C5H12 - pentane;
- C6H14 - Hexane;
- C7H16 - heptane;
- C8H18 - octane;
- C9H20 - nonane;
- C10H22 - Dean;
- C11H24 - undecane;
- C12H26 - dodecane;
- C13H28 - tridecane;
- C14H30 - tetradecane;
- C15H32 - pentadecane;
- C16H34 - hexadecane;
- C17H36 - heptadecane;
- C18H38 - octadecane;
- C19H40 - nonadecan;
- C20H42 - eicosane and so on.
chemical properties of alkanes have low activity.This is due to the relative strength of the non-polar C-C and low-C-H bonds, as well as the saturated molecules.All atoms are linked by a single σ-bonds, which are difficult to break down because of their low polarizability.Breaking them can be realized only under certain conditions, with the formation of radicals, which are the names of the paraffin compounds with replacement of the end.For example, propane - propyl (C3H7-), ethane - ethyl (C2H5-), methane - methyl (CH3-) and so on.
chemical properties of alkanes talking about the inertia of these compounds.They are not capable of addition reactions.Typical of these are a substitution reaction.Oxidation (combustion) of paraffinic hydrocarbons takes place only at elevated temperatures.They can be oxidized to alcohols, aldehydes and acids.As a result kreginga (the process of thermal cracking of hydrocarbons) higher alkanes at a temperature of 450 to 550 ° C may form saturated hydrocarbons with a lower molecular weight.With increasing temperature, the thermal decomposition is called pyrolysis.
alkanes Chemical properties depend not only on the number of carbon atoms in the molecule, but also on the structure.All normal paraffins can be separated (one C atom can be connected with not more than two carbon atoms) and iso-structure (C atom can be connected to four other C-atoms through this molecule has a spatial structure).For example, pentane, and 2,2-dimethylpropane have the same molecular weight and the chemical formula C5H12, but the chemical and physical properties, they are different: mp 129.7 ° C minus and minus 16.6 ° C, boiling point 36,1 ° Cand 9,5 ° C, respectively.Isomers easier to enter into chemical reactions than hydrocarbons of normal structure with the same number of atoms C.
characteristic chemical properties of alkanes - a substitution reaction, which include halogenation or sulfonation.The reaction of chlorine with paraffin by a radical mechanism under the influence of heat or light generated chlorinated methane CH3Cl chloromethane, dichloromethane, CH2Cl2, CHCl3 trichloromethane and carbon tetrachloride CCl4.Sulfonation alkanes under UV light, sulfonyl chlorides are obtained: R-H + SO2 + Cl2 → R-SO2-Cl + HCl.These substances are used in the production of surfactants.
