How to make isomers and homologues? How to make isomers of alkanes?

Before analyzing how to make isomers of limit hydrocarbons, we will reveal the features of this class of organic substances.

Saturated hydrocarbons

In organic chemistry, many classes of CxHy are distinguished. Each has its own general formula, homology series, qualitative reactions, application. Saturated hydrocarbons of the alkane class are characterized by single bonds (sigma). The general formula for this class of organic substances is CnH2n + 2. This explains the main chemical properties: substitution, combustion, oxidation. Paraffins are not characterized by addition, since the bonds in the molecules of these hydrocarbons are single.

Isomerism

Such phenomenon as isomerism explains the variety of organic substances. By isomerism, it is customary to understand the phenomenon in which there are several organic compounds having the same quantitative composition (the number of atoms in the molecule), but their different arrangement in the molecule. The resulting substances are called isomers. They can be representatives of several classes of hydrocarbons, and therefore differ in chemical properties. Different compounds in the molecule of alkanes of C atoms lead to the appearance of structural isomerism. How to make isomers of alkanes? There is a certain algorithm, according to which it is possible to depict the structural isomers of a given class of organic substances. There is a similar possibility with only four carbon atoms, that is, with the butane molecule C4H10.

Varieties of isomerism

In order to understand how to make isomer formulas, it is important to have an idea of its forms. If there are identical atoms inside the molecule in equal amounts, arranged in space in different orders, we are talking about spatial isomerism. Otherwise, it is called stereoisomerism. In such a situation, the use of structural formulas alone is clearly not enough; it will require the use of special projection or spatial formulas. The limiting hydrocarbons, starting with H3C-CH3 (ethane), have different spatial configurations. This is due to the rotation of the molecule inside the C-C bond. It is a simple σ-bond that creates a conformational (rotational) isomerism.

Structural isomerism of paraffins

Let's talk about how to make isomers of alkanes. The class has a structural isomerism, that is, the carbon atom forms different chains. Otherwise, the possibility of changing the position in the chain of carbon atoms is called the isomerism of the carbon skeleton.

Isomers of heptane

So, how to leave isomers for a substance having the composition of C7H16? First, you can arrange all the carbon atoms in one long chain, add a certain number of C atoms for each. How many? Given that the carbon valence is four, the outermost atoms will have three hydrogen atoms, and the inner atoms have two hydrogen atoms. The resulting molecule has a linear structure, such a hydrocarbon is called n-heptane. The letter "n" means a straight carbon skeleton in this hydrocarbon.

Now we change the arrangement of carbon atoms, "shortening" the straight carbon chain in C7H16. It is possible to compose isomers in expanded or shortened structural form. Consider the second option. First, we arrange one C atom in the form of a methyl radical in different positions.

This isomer of heptane has the following chemical name: 2-methylhexane. Now we "move" the radical to the next carbon atom. The resulting limiting hydrocarbon is called: 3-methylhexane.

If we continue to move the radical, the numbering will begin on the right side (the hydrocarbon radical is closer to the beginning), that is, we will get an isomer that we already have. Therefore, thinking about how to make isomer formulas for the original substance, let's try to make the skeleton even "shorter".

The remaining two carbon can be represented as two free radicals - methyl.

We first arrange them for different carbons entering the main chain. We call the obtained isomer -2,3 dimethylpentane.

Now we leave one radical in the same place, and the second we transfer to the next carbon atom of the main chain. This substance is called 2,4-dimethylpentane.

Now arrange the hydrocarbon radicals from one carbon atom. First, the second, we get 2,2 dimethylpentane. Then at the third, obtaining 3,3 dimethylpentane.

Now we leave in the main chain four carbon atoms, the remaining three we use as methyl radicals. We arrange them as follows: two for the second atom C, one for the third carbon. We call the obtained isomer: 2,2, 3 trimethylbutane.

Using the example of heptane, we analyzed how correctly to make isomers for the ultimate hydrocarbons. The photo shows examples of structural isomers for butene6 of its chloro derivatives.

Alkenes

This class of organic substances has the general formula CnH2n. In addition to saturated C-C bonds, there is also a double bond in this class. It determines the main properties of this series. Let's talk about how to leave isomers of alkenes. Let's try to identify their differences from the ultimate hydrocarbons. In addition to the isomerism of the main chain (structural formulas), three more types of isomers are also characteristic of representatives of this class of organic hydrocarbons: geometric (cis and transform), multiple bond positions, and interclass isomerism (with cycloalkanes).

Isomers of C6H12

Let's try to find out how to compose the isomers c6h12, given the fact that the substance with this formula can belong directly to two classes of organic substances: alkenes, cycloalkanes.

First, let's think about how to make isomers of alkenes, if there is a double bond in the molecule. We put a straight carbon chain, put a multiple bond after the first carbon atom. Let's try not only to compose the isomers of c6n12, but also to name the substances. This substance - hexene - 1. The figure indicates the position in the double bond molecule. When it moves along a carbon chain, we get hexene-2, as well as hexene-3

Now we are discussing how to make isomers for a given formula, changing the number of atoms in the main circuit.

First, we shorten the carbon skeleton to one carbon atom, it will be considered as a methyl radical. We leave the double bond after the first atom C. The obtained isomer from the systematic nomenclature will have the following name: 2 methylpentene - 1. Now we move the hydrocarbon radical along the main chain, leaving the position of the double bond unchanged. This unsaturated hydrocarbon of a branched structure is called 3 methylpentene-1.

A further isomer is possible without changing the main chain and the double bond position: 4 methylpentene-1.

For the composition of C6H12, you can try to move the double link from the first to the second position, without converting the main chain itself. The radical will then move along the carbon skeleton, beginning with the second atom C. This isomer is called 2 methylpentene-2. In addition, it is possible to place the radical CH3 of the third carbon atom, while obtaining 3 methyl pentene-2

If a radical is placed on the fourth carbon of an atom in a given chain, another new substance is formed, an unsaturated hydrocarbon with a sinuous carbon skeleton - 4 methylpentene-2.

With further reduction of the number C in the main chain, one can obtain another isomer.

We leave the double bond after the first carbon atom, and put two radicals to the third atom C of the main chain, we obtain 3,3 dimethylutene-1.

Now we put radicals at neighboring carbon atoms, without changing the position of the double bond, we get 2,3 dimethylbutene-1. Let's try, without changing the size of the main chain, to move the double link to the second position. Radicals in this case we can supply only 2 and 3 C atoms, yielding 2.3 dimethylbutene-2.

There are no other structural isomers for this alkene, any attempts to come up with them will lead to a violation of the theory of the structure of organic substances of AM Butlerov.

The spatial isomers of C6H12

Now we will find out how to make isomers and homologues from the point of view of spatial isomerism. It is important to understand that the cis and trans forms of alkenes are possible only for the position of the double bond 2 and 3.

When the hydrocarbon radicals are in the same plane, a cis-measurement of hexene-2 is formed, and when the radicals are located in different planes, the trans-form of hexene is 2.

Interclass isomers of C6H12

Arguing over how to make isomers and homologues, one should not forget about such an option as inter-class isomerism. For unsaturated hydrocarbons of the series of ethylene having the general formula CnH2n, such isomers are cycloalkanes. A feature of this class of hydrocarbons is the presence of a cyclic (closed) structure with saturated single bonds between carbon atoms. It is possible to formulate the formulas of cyclohexane, methylcyclopentane, dimethylcyclobutane, trimethylcyclopropane.

Conclusion

Organic chemistry is multifaceted, mysterious. The quantity of organic substances exceeds in hundreds times the number of inorganic compounds. This fact is easily explained by the existence of such a unique phenomenon as isomerism. If in one homologous series there are similar substances and structures, then when the position of the carbon atoms in the chain changes, new compounds appear called isomers. Only after the appearance of the theory of the chemical structure of organic substances, it was possible to classify all the hydrocarbons, to understand the specificity of each class. One of the propositions of this theory directly concerns the phenomenon of isomerism. The great Russian chemist was able to understand, explain, prove that the chemical properties of the substance, its reactive activity, practical application depend on the location of the carbon atoms. If we compare the number of isomers formed by limiting alkanes and unsaturated alkenes, alkenes, of course, are leading. This is explained by the fact that in their molecules there is a double bond. It is this substance that allows this class of organic substances to form not only alkenes of different types and structures, but also to talk about the metabolic isomerism with cycloalkanes.