Cycloalkanes are hydrocarbons that have closed structures in their composition. Consider the features of these compounds, their scope.
Class features
What are cycloalkanes? The formula of the class CnH2n indicates a lack of hydrogen atoms. A similar situation involves two scenarios. Either a double bond must be present in the structure, or a closed structure is contained in the molecule. What structure do cycloalkanes have? Their formula corresponds to the second case, that is, the presence of a closed structure in the molecule. It is the specificity of the structure that determines the characteristics of the physical and chemical properties of this class of hydrocarbons.
How many different cycloalkanes does C4H8 have? To find the answer to this question, it is necessary to analyze those types of isomerism that are characteristic of cycloalkanes. Two isomers with such a qualitative and quantitative composition can have a cyclic structure: cyclobutane, methylcyclopropane. A similar option is called isomerism of the side chain.
Since cycloalkanes are interclass isomers of unsaturated olefins, one can consider the formulas of substances that contain a double bond. In this form, two structures can exist: butene-1 and butene-2. Answering the question of how many different cycloalkanes can exist for the proposed formula, it is necessary to consider not only cycloalkanes, but also alkenes. Only in this case it will be possible to present the correct answer.
So, cycloalkanes are hydrocarbons that have at least two types of isomerism.
Features of the item
The names of specific hydrocarbons of cyclic composition are given in full accordance with international nomenclature. For the basis, the amount of carbon in the closed chain is used. Next, the atoms in the side chain are taken into account. For example, methylcyclopropane. Cycloalkanes are compounds in which carbon atoms are in the sp3 hybrid state, similar to saturated hydrocarbons. A similar feature determines the main methods of preparation and the characteristic properties of this class.
Options for obtaining cycloalkanes
How can I get cycloalkanes? Examples of the main reactions indicate that there are several options for their formation. For example, cyclohexane is formed by hydrogenation of aromatic benzene. Compounds with three, four carbon atoms in the cycle can be obtained by the removal of halogens from molecules of dihalogenated alkanes. Cycloalkanes are also obtained by pyrolysis of salts of dicarboxylic organic acids. Heating without the presence of air leads to the formation of cyclopentane and cyclohexane.
Chemical properties
The chemical properties of naphthenes are similar to saturated hydrocarbons. They are characterized by substitutional reactions with halogens. In addition, representatives of naphthenes enter into a chemical interaction with nitric acid. Cycloalkanes are resistant to concentrated sulfuric acid. A reaction with chlorosulphuric acid and oleum is also possible: as a result, sulfur oxide is formed (4).
Naphthenes having 5 and 6 carbon atoms in the molecules are considered chemically stable compounds. But when exposed to bromide or aluminum chloride, their isomerization occurs, accompanied by a narrowing or expansion of the original cycle.
Isomerization
For example, in the process of isomerization, cyclohexane forms methylcyclopentane. A variety of derivatives of cyclopentane and cyclohexane were found in oil, the remaining representatives of naphthenes are practically absent in it.
Distinctive features of middle cycles are considered the ability to form such conformations in which some carbon atoms are directed not outward, but inside the cycle. Such bonds are called intranular, and those inside the ring are called extranular bonds.
For example, for cyclodecane, in the most favorable conformation, six intranular and fourteen extranular hydrogen atoms are assumed. This implies the inequality of the CH2 groups, which is reflected in an increase in the binding energy, and helps to improve the chemical properties of this compound.
For hydrocarbons with 12 or more carbon atoms, conformational mobility is characteristic. Since free rotation is possible via the CC bond, the existence of trans and cis forms is not assumed for such compounds.
Cyclanes (naphthenes) can be contained with natural oil in the range of 25 to 75 percent. Their quantitative content depends on the weighting of the fraction. In oil fractions that have high boiling points, an increase in the number of aromatic structures occurs. Especially a lot of naphthenes are found in emben and Baku oils.
In a quantitative ratio, indicators are up to 80 percent. The relationship between the types of oil and the distribution of cycloalkanes in fractions is revealed. Monocyclic hydrocarbons, which have a long alkyl side chain, are considered less thermodynamically stable. The distribution of CnH2n by structure type is directly related to the temperatures used in the distillation of oil.
For example, monocyclic naphthenes are not detected in the temperature range of 300-350 degrees Celsius, and bicyclic compounds disappear when the temperature exceeds 400 degrees Celsius.
Cyclopropane Characterization
C3H6 is the simplest representative of naphthenes. It is a gaseous substance with little solubility in water. Among the main chemical properties characteristic of this organic compound, we distinguish catalytic hydrogenation. The product of this interaction will be a saturated hydrocarbon propane. In addition, cyclopropane, like other hydrocarbons, interacts with atmospheric oxygen, forming carbon dioxide, water vapor, and a sufficient amount of energy.
Features of representatives of this class
If we compare the boiling points of representatives of the class of cycloalkanes with indicators for alkanes having a similar number of carbon atoms, they will be slightly higher. The reason is the cyclical structure of this class. The density of naphthenes is higher than that for alkanes, but slightly inferior to arenas.
To understand how many different cycloalkanes correspond to one formula, it is necessary to compose variants of isomers not only of a cyclic type, but also with a straight skeleton, which contains a double bond. In the presence of substituents in the molecule in the form of hydrocarbon radicals, the melting point of the cycloalkane decreases.
If we analyze the physical and chemical properties of this class of hydrocarbons, we can conditionally subdivide the substances into compounds with small cycles (three to four), standard (five, six, seven), medium (eight to twelve), as well as large cycles (from twelve carbons).
Areas of use
Let's talk about what the main use of cycloalkanes is. Naphthenes are used in medicine. For example, cyclopropane is a drug. Cyclopentane is considered a good solvent, it is in demand in organic synthesis. Cyclohexane is necessary in the chemical reaction of the synthesis of nylon, nylon (production of polyamide fibers), in addition, it is in demand for the production of benzene. Saturated alkanes and cycloalkanes have little reactivity. This fact can be explained by the insignificant polarity of the CC bond. In addition, a significant number of cycloalkanes are used in the chemical industry.
Conclusion
Mixtures of naphthenes and individual hydrocarbons are used for the manufacture of lubricants. Representatives of this class of hydrocarbons are able to improve the operational characteristics of diesel fuel. For example, the addition of cycloalkanes significantly increases the octane number, increases the viscosity, increases the calorific value of the engine. That is why cycloalkanes are not isolated from oil products, but left in the gasoline fraction.
Naphthenic concentrates are used as organic solvents. Cycloalkanes with average molecular weights are in demand in the production of synthetic detergents. A sufficient amount of naphthenes is also used as fuel, since a considerable amount of heat is generated during their combustion.