Saturated hydrocarbons (paraffins) are saturated aliphatic hydrocarbons, where there is a simple (single) bond between carbon atoms.
All other valences are fully saturated with hydrogen atoms.
Homological series
Ultimate saturated hydrocarbons have the general formula SpH2p+2. Under normal conditions, representatives of this class show a weak reactivity, so they are called "paraffins". Saturated hydrocarbons start with methane, which has the molecular formula CH4.
Structure features on the example of methane
This organic substance is odorless and colorless, the gas is almost twice as light as air. In nature, it is formed during the decomposition of animal and plant organisms, but only in the absence of air access. It is found in coal mines, in swampy reservoirs. In small quantities, methane is part of natural gas, which is currently used as a fuel in production, in everyday life.
This saturated hydrocarbon belonging to the class of alkanes has a covalent polar bond. The tetrahedral structure is explained by sp3hybridization of a carbon atom, the bond angle is 109°28'.
Nomenclature of paraffins
Saturated hydrocarbons can be named according to systematic nomenclature. There is a certain procedure that allows you to take into account all the branches that are present in the molecule of the saturated hydrocarbon. First you need to identify the longest carbon chain, then number the carbon atoms. To do this, select the part of the molecule in which there is a maximum branching (a greater number of radicals). If there are several identical radicals in the alkane, specifying prefixes are indicated with their name: di-, tri-, tetra. Numbers are used to clarify the position of active particles in a hydrocarbon molecule. The final step in the name of paraffins is the indication of the carbon chain itself, with the addition of the suffix -an.
Saturated hydrocarbons differ in their state of aggregation. The first four representatives of this cash register are gaseous compounds (from methane to butane). As the relative molecular weight increases, there is a transition to a liquid, and then to a solid state of aggregation.
Saturated and unsaturated hydrocarbons do not dissolve in water, but can dissolve in organic solvent molecules.
Features of isomerism
What types of isomerism do saturated hydrocarbons have? Examples of the structure of representatives of this class, starting with butane, indicatepresence of isomerism of the carbon skeleton.
The carbon chain formed by covalent polar bonds has a zigzag shape. This is the reason for the change in the main chain in space, that is, the existence of structural isomers. For example, when changing the arrangement of atoms in a butane molecule, its isomer is formed - 2methylpropane.
Chemical properties
Let's consider the basic chemical properties of saturated hydrocarbons. For representatives of this class of hydrocarbons, addition reactions are not characteristic, since all bonds in the molecule are single (saturated). Alkanes enter into interactions associated with the replacement of a hydrogen atom by a halogen (halogenation), a nitro group (nitration). If the formulas of saturated hydrocarbons have the form SpH2n + 2, then after substitution a substance of the composition CnH2n + 1CL is formed, as well as CnH2n + 1NO2.
The substitution process has a free radical mechanism. First, active particles (radicals) are formed, then the formation of new organic substances is observed. All alkanes react with representatives of the seventh group (main subgroup) of the periodic table, but the process proceeds only at an elevated temperature, or in the presence of a light quantum.
Also, all representatives of the methane series are characterized by interaction with atmospheric oxygen. During combustion, carbon dioxide and water vapor act as reaction products. The reaction is accompanied by the formation of a significant amount of heat.
When methane interacts with atmospheric oxygenan explosion is possible. A similar effect is typical for other representatives of the class of saturated hydrocarbons. That is why a mixture of butane with propane, ethane, methane is dangerous. For example, such accumulations are typical for coal mines, industrial workshops. If the saturated hydrocarbon is heated above 1000 °C, it decomposes. Higher temperatures lead to the production of unsaturated hydrocarbons, as well as to the formation of hydrogen gas. The dehydrogenation process is of industrial importance, it makes it possible to obtain a variety of organic substances.
For hydrocarbons of the methane series, starting with butane, isomerization is characteristic. Its essence lies in changing the carbon skeleton, obtaining saturated branched hydrocarbons.
Application features
Methane as natural gas is used as a fuel. Chlorine derivatives of methane are of great practical importance. For example, chloroform (trichloromethane) and iodoform (triiodomethane) are used in medicine, and carbon tetrachloride in the process of evaporation stops the access of atmospheric oxygen, so it is used to extinguish fires.
Due to the high value of the calorific value of hydrocarbons, they are used as fuel not only in industrial production, but also for domestic purposes.
A mixture of propane and butane, called "liquefied gas", is especially relevant in areas where natural gas is not available.
Interesting facts
Representatives of hydrocarbons, which are in a liquid state, are fuel for internal combustion engines in cars (gasoline). In addition, methane is an affordable raw material for various chemical industries.
For example, the reaction of decomposition and combustion of methane is used for the industrial production of soot, which is necessary for the production of printing ink, as well as the synthesis of various rubber products from rubber.
To do this, such a volume of air is supplied to the furnace along with methane so that partial combustion of saturated hydrocarbon occurs. As the temperature rises, some of the methane will decompose, producing fine soot.
Formation of hydrogen from paraffins
Methane is the main source of industrial hydrogen used for ammonia synthesis. To carry out dehydrogenation, methane is mixed with steam.
The process takes place at a temperature of about 400 °C, a pressure of about 2-3 MPa, aluminum and nickel catalysts are used. In some syntheses, a mixture of gases is used, which is formed in this process. If subsequent transformations involve the use of pure hydrogen, in this case, catalytic oxidation of carbon monoxide with water vapor is carried out.
Chlorination produces a mixture of methane chlorine derivatives, which have a wide industrial application. For example, chloromethane is able to absorb heat, which is why it is used as a refrigerant in modern refrigeration systems.
Dichloromethane is a good solvent for organic substances, used in chemical synthesis.
Hydrogen chloride, formed in the process of radical halogenation, after dissolving in water, becomes hydrochloric acid. Currently, acetylene is also obtained from methane, which is a valuable chemical raw material.
Conclusion
Representatives of the methane homologous series are widely distributed in nature, which makes them popular substances in many branches of modern industry. From methane homologues, branched hydrocarbons can be obtained, which are necessary for the synthesis of various classes of organic substances. The highest representatives of the alkanes class are the raw materials for the production of synthetic detergents.
In addition to paraffins, alkanes, cycloalkanes, called cycloparaffins, are also of practical interest. Their molecules also contain simple bonds, but the peculiarity of the representatives of this class is the presence of a cyclic structure. Both alkanes and cycloacanes are used in large quantities as gaseous fuels, since the processes are accompanied by the release of a significant amount of heat (exothermic effect). Currently, alkanes, cycloalkanes are considered the most valuable chemical raw materials, so their practical use is not limited to typical combustion reactions.
