Alkanes, alkenes, alkynes, alkadienes, the formulas of which differ in the number of hydrogen atoms, belong to hydrocarbons. Consider the distinctive features of each class, the type of hybridization, characteristic properties.
Paraffins
Marginal hydrocarbons have the general formula C p H 2p + 2 . In them, all bonds between hydrogen and carbon atoms are single. If only hydrogen is detached in the reaction, the alkane turns into an active particle - a radical. The first representatives of this series are gaseous substances that are slightly soluble in water.
With an increase in the number of carbons in the main chain, the solubility decreases, and hydrocarbons pass into a solid state of aggregation under normal conditions.
Among the main chemical properties inherent in representatives of this class, we single out the substitution. Due to the fact that all bonds are saturated, addition to alkanes is uncharacteristic. Like all other organic substances, alkanes react with oxygen (combustion), as a result of which energy is released. This process is endothermic, used in production for heating residential and industrial premises.
Cycloalkanes
A feature of this class is the presence of a closed molecular structure. The general formula of such hydrocarbons is of the form C p H 2p . Given the structural features of this class, they are characterized by substitution reactions in the side chain, as well as the addition of hydrogen, which is accompanied by the destruction of the cycle.
Alkenes
In the homologous series of ethylene, the general formula has the form C n H 2n + 2 . Among the distinctive features of hydrocarbons (naphthenes), we highlight the presence of a double bond between carbon atoms. A pi bond is formed due to the overlap of two non-hybrid p-orbitals at adjacent carbon atoms.
Its presence determines not only the type of carbon hybridization in alkenes, but also the characteristic chemical properties of all representatives of this class of organic compounds. A qualitative reaction to an unsaturated (double) bond will be the discoloration of bromine water.
As a result of the interaction, a double bond is cleaved, and a halogen molecule is attached to the alkene. In addition, bleaching of potassium permanganate also applies to specific reactions characteristic of this homologous series.
Among the properties of ethylene and its homologues, it is necessary to distinguish other types of addition reactions. During hydrogenation (interaction with hydrogen), the formation of the corresponding alkane occurs. Hydration (with water) and hydrohalogenation (with a hydrogen halide molecule) occur in unsaturated alkenes according to the Markovnikov rule.
Its essence lies in the fact that when a molecule of water or hydrogen halide is attached to an asymmetric alkene (bond position 1), a double bond splits. Hydrogen is attached in the interaction to a more hydrogenated (hydrogenated) carbon atom, and a hydroxo group or halogen is attached to less hydrogenated N.
In addition to addition, polymerization reactions are characteristic of ethylene and its homologues. A large polymer molecule consisting of the same structural units is formed from a small initial monomer. Polymerization is widely used in the chemical industry to create modern plastics.
Alkadienes
To begin with, we note that alkadienes are unsaturated hydrocarbons having the general formula C p H 2n + 2 . There is a certain similarity of representatives of this homologous series with alkenes. Since alkadienes are unsaturated hydrocarbons, addition reactions are also characteristic of them.
The difference is that there are two unsaturated double bonds in the dienes, so an excess of bromine water, hydrogen, water, and hydrogen halide is required for complete attachment.
Representatives of a number of propadiene enter into the polymerization reaction. The products obtained during this reaction are used for the production of synthetic rubbers and rubber. Since alkadienes are unsaturated substances, a qualitative reaction for their determination will be the discoloration of potassium permanganate and bromine water. Alkadienes, the homologous series of which begins with propadiene, are liquids or solids.
Among the applications of representatives of this class, we single out the production of polymer materials.
Alkins
In the homologous series of acetylene, the general formula has the form C p H 2p-2 . If alkadienes are substances in which there are two double bonds, then alkynes are characterized by one triple bond. A qualitative response to a triple bond for asymmetric alkynes is the interaction of representatives of this class with a complex compound - silver diamine hydroxide (1). As a result of the interaction, a salt is formed - silver acetylenide.
Representatives of this homologous series are interclass isomers for alkadienes. Like alkenes, alkadienes, all alkynes undergo addition reactions with halogens, hydrogen, hydrogen halide, water. When an insufficient amount of hydrogen is attached to the acetylene molecule, ethylene is formed. In the case of interaction with an excess of hydrogen, ethane (saturated hydrocarbon) is formed from acetylene.
Conclusion
Alkines, alkenes, alkadienes, alkadienes, the chemical properties of which were considered above, clearly demonstrate the main similarities and differences between different classes of substances. All hydrocarbons in their composition have carbon and hydrogen atoms, therefore they are an excellent type of fuel.