Consider aromatic hydrocarbons. The formula for the representatives of this homologous series is SpN2p-6.
Class features
At the beginning of the nineteenth century, Faraday discovered benzene - C6H6. Compared to saturated hydrocarbons, the structural formulas of aromatic hydrocarbons are presented as cycles. Given that the molecule does not contain enough hydrogen, an aromatic ring forms inside the ring.
How to burn aromatic hydrocarbons? The formula proposed by Kekule explains the structure of this class of hydrocarbons. The presence of double bonds confirms the aromatic nature of benzene and its homologs.
Chemical properties
The general formula of aromatic hydrocarbons implies the existence of all compounds of this class of addition reactions: hydrogenation, halogenation, hydration. The results of numerous experiments have shown insignificant chemical activity of benzene.
It exhibits increased oxidation resistance, is capable of joining only in the presence of ultraviolet radiation or elevated temperature.
Features of the structure of benzene
The molecular formula of the aromatic hydrocarbon is C6H6. All carbon atoms are in the cp2 hybrid state and are located in the same plane. Each of them has one non-hybrid atom C left, which are combined into a common electron cloud located perpendicular to the plane of the ring. This cyclic system of conjugated p-bonds determines the chemical passivity of benzene.
The American chemist L. Pauling proposed to consider benzene in the form of two interconnected structures that differ in the distribution of electron density, turning into each other.
Nomenclature and isomerism
What can be called aromatic hydrocarbons? The formula of all compounds that belong to a number of aromatic hydrocarbons should correspond to the proposed molecular structure. The simplest homologue of benzene is toluene. The difference between it and the simplest aromatic hydrocarbon is CH2.
In the name of representatives of this class, benzene is taken as the basis. The carbon atoms are numbered clockwise, starting from the oldest to the youngest substituent. Even (2 and 6) positions are considered ortho-positions, and 3 and 5 (odd) meta-variants.
Characterization of physical properties
What physical characteristics do aromatic hydrocarbons possess, the class formula of which corresponds to SpN2p-6?
Under normal conditions, benzene, as well as its nearest homologs, are toxic liquids with an unpleasant characteristic odor. All arenas are characterized by low solubility in water. In unlimited quantities, they are able to dissolve in organic solvents.
Receipt options
As an industrial option for the production of benzene and other representatives of the class of aromatic hydrocarbons, we can consider the processing of coal tar or oil. The synthetic option for obtaining representatives of this class is as follows:
- cleavage of hydrogen molecules from cycloparaffins (dehydrogenation);
- aromatization of saturated hydrocarbons (alkanes).
Both proposed methods for the conversion of compounds into an aromatic variant involve the use of elevated temperature and a catalyst.
Among the common methods for laboratory preparation of arenas, Würz synthesis can be mentioned. It is characterized by the interaction of a halogenated alkane with metallic sodium.
Features of benzene homologues
Toluene, in which a methyl group is present, reacts faster than benzene. Since CH3 is a first-order orientant, incoming substituents will be oriented in ortho (even) positions. Toluene is capable of halogenation (chlorination, bromination, iodination), as well as nitration.
Conclusion
All aromatic hydrocarbons correspond to the general formula SpN2p-6. When they are burned in air oxygen, a sufficient amount of soot is released, which is easily explained by the increased carbon content in them.