Cycloalkanes are ... Cycloalkanes: preparation, formula, chemical and physical properties

Cycloalkanes are hydrocarbons, which in their composition have closed structures. Consider the features of these compounds, their scope.

Class Features

What are the cycloalkanes? The formula for the CnH2n class indicates a shortage of hydrogen atoms. This situation assumes two development scenarios. Either in the structure there must be a double bond, or the molecule contains a closed structure. What structure have cycloalkanes? 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 specific physical and chemical properties of this class of hydrocarbons.

How many different cycloalkanes correspond to the composition of C4H8? To find the answer to this question, it is necessary to analyze the types of isomerism that are characteristic of cycloalkanes. Two isomers with such qualitative and quantitative composition can have a cyclic structure: cyclobutane, methylcyclopropane. This is called the side chain isomerism.

Since cycloalkanes are interclass isomers of unsaturated olefins, it is possible to consider formulas of substances in which there is a double bond. In this form, there may exist two structures: butene-1 and butene-2. Answering the question about 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, which have at least two kinds of isomerism.

Nomenclature Features

The names of specific hydrocarbons of cyclic composition are given in full accordance with the international nomenclature. The basis uses the amount of carbon in the closed circuit. Next, take into account the atoms available in the side chain. For example, methylcyclopropane. Cycloalkanes are compounds in which the carbon atoms are in the sp3 hybrid state, similar to the limiting hydrocarbons. This feature determines the main methods of obtaining and the characteristic properties of this class.

Variants for the preparation of 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 ring can be obtained by cleavage of halogens from molecules of dihalogenated alkanes. Also, cycloalkanes are obtained by the pyrolysis of salts of dicarboxylic organic acids. Heating without the presence of air leads to the formation of cyclopentane and cyclohexane.

Chemical properties

By chemical properties, naphthenes are similar to the ultimate hydrocarbons. They are characterized by reactions with halogens by substitution. In addition, representatives of naphthenes react chemically with nitric acid. Cycloalkanes are resistant to concentrated sulfuric acid. With chlorosulfuric acid and oleum, the reaction is also possible: eventually, sulfur oxide is formed (4).

Naphthenes, having in molecules of 5 and 6 carbon atoms, are considered to be chemically stable compounds. But when exposed to them with bromide or aluminum chloride, their isomerization occurs, accompanied by a narrowing or widening of the initial cycle.

Isomerization

For example, in the process of isomerization, cyclohexane forms methylcyclopentane. In the oil, various derivatives of cyclopentane and cyclohexane were found, the rest of the naphthenes in it are practically absent.

Distinctive features of average cycles are the ability to form conformations in which some carbon atoms are directed not outward, but inside the cycle. Such connections are called intranular, and those that are inside the ring are called extranular connections.

For example, for cyclodechane, six intranular and fourteen extranular hydrogen atoms are assumed in the most advantageous conformation. This implies the unequality of the CH2 groupings, which reflects the increase in binding energy, contributes to the improvement of the chemical properties of this compound.

For hydrocarbons with 12 or more carbon atoms, conformational mobility is characteristic. Since free rotation is possible through the CC bond, no trans- and cis forms exist for such compounds.

Cyclones (naphthenes) can be contained with natural oil ranging from 25 to 75 percent. The quantitative content of these depends on the weighting of the fraction. In oil fractions, which have high boiling points, an increase in the amount of aromatic structures occurs. Especially a lot of naphthenes were found in the embmen and Baku oil.

In a quantitative ratio, the figures are up to 80 percent. The dependence between the types of oil and the distribution of cycloalkanes on fractions was revealed. Less thermodynamically resistant are monocyclic hydrocarbons, which have a long side alkyl chain. The distribution of CnH2n by type of structure is directly related to the temperatures used in the distillation of oil.

For example, monocyclic naphthenes are not detected at a temperature range of 300-350 degrees Celsius, and bicyclic compounds disappear when the temperature is exceeded by 400 degrees Celsius.

Characterization of cyclopropane

C3H6 is the simplest representative of naphthenes. It is a gaseous substance with little solubility in water. Among the basic chemical properties characteristic of this organic compound, we select catalytic hydrogenation. The product of this interaction is the ultimate hydrocarbon propane. In addition, cyclopropane, like other hydrocarbons, reacts with air oxygen, forming carbon dioxide, water vapor, sufficient energy.

Features of representatives of this class

If we compare the boiling points of representatives of the cycloalkane class with those for alkanes having a similar number of carbon atoms, they will be slightly higher. The reason lies in 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 cyclic form, but also with a direct skeleton, in which there is a double bond. When there are substituents in the molecule in the form of hydrocarbon radicals, the melting temperature of the cycloalkane decreases.

If we analyze the physical and chemical properties of this class of hydrocarbons, we can perform a conditional subdivision of substances into compounds with small cycles (three to four), standard (five, six, seven), medium (from eight to twelve), and also with large cycles Twelve carbons).

Spheres of use

Let's talk about the main application of cycloalkanes. Naphthenes are used in medicine. For example, cyclopropane is a narcotic drug. Cyclopentane is considered a good solvent, it is in demand in organic synthesis. Cyclohexane is necessary in the chemical reaction for the synthesis of nylon, kapron (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 negligible polarity of the C-C bond. In addition, a significant amount of cycloalkanes is used in the chemical industry.

Conclusion

Naphthene mixtures and individual hydrocarbons are used for the manufacture of lubricants. Representatives of this class of hydrocarbons can improve the performance of diesel fuel. For example, the addition of cycloalkanes significantly increases the octane number, increases the viscosity, increases the heat of combustion of the engine. This is why cycloalkanes are not isolated from refined products, but are left in the gasoline fraction.

Concentrates of naphthenes are used in the form of organic solvents. Cycloalkanes with average molecular weights are in demand in the production of synthetic detergents. A sufficient number of naphthenes is also used as fuel, since during their combustion a considerable amount of heat is released.