Before analyzing how to make isomers of saturated hydrocarbons, we reveal the features of this class of organic substances.
Saturated hydrocarbons
In organic chemistry, many CxHy classes stand out. Each has its own general formula, homologous series, qualitative reactions, application. Saturated hydrocarbons of the alkane class are characterized by single (sigma) bonds. The general formula for this class of organic substances is CnH2n + 2. This explains the basic chemical properties: substitution, combustion, oxidation. Attachment is not characteristic for paraffins, since the bonds in the molecules of these hydrocarbons are single.
Isomerism
Such a phenomenon as isomerism explains the diversity of organic substances. Isomerism is understood to mean a phenomenon in which there are several organic compounds having the same quantitative composition (the number of atoms in a 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. A different compound in the molecule of alkanes of C atoms leads 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 this 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 formulate isomer formulas, it is important to have an idea of its types. If there are equal atoms inside the molecule in equal numbers, which are located in space in different order, we are talking about spatial isomerism. Otherwise, it is called stereoisomerism. In such a situation, the use of structural formulas alone will not be enough, the use of special projection or spatial formulas will be required. Marginal hydrocarbons, starting with H3C – CH3 (ethane), have different spatial configurations. This is due to rotation inside the molecule at the C – C bond. It is a simple σ-bond that creates the conformational (rotational) isomerism.
Structural isomerism of paraffins
Let's talk about how to make isomers of alkanes. The class has 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.
Heptane isomers
So, how to leave isomers for a substance having the composition of C7H16? To begin with, you can arrange all the carbon atoms in one long chain, add for each a certain number of atoms C. How many? Considering that the valency of carbon is four, the outer atoms will have three hydrogen atoms, and the inner atoms will have two. The resulting molecule has a linear structure, such a hydrocarbon is called n - heptane. The letter “n” refers to the straight carbon skeleton in a given hydrocarbon.
Now we change the arrangement of carbon atoms, while “shortening” the direct carbon chain in C7H16. It is possible to make isomers in expanded or reduced structural form. Consider the second option. First, we place one C atom in the form of a methyl radical in different positions.
This heptane isomer has the following chemical name: 2-methylhexane. Now we “move” the radical to the next carbon atom. The resulting saturated hydrocarbon is called: 3-methylhexane.
If we move the radical further, the numbering will begin on the right side (the hydrocarbon radical is located closer to the beginning), that is, we will get the isomer that we already have. Therefore, thinking about how to make isomer formulas for the starting material, we will 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 in the main chain. We call the resulting isomer -2.3 dimethylpentane.
Now leave one radical in the same place, and transfer the second to the next carbon atom of the main chain. This substance is called 2,4 dimethylpentane.
Now we place hydrocarbon radicals at one carbon atom. First, the second, we get 2.2 dimethylpentane. Then the third, receiving 3.3 dimethylpentane.
Now we leave four carbon atoms in the main chain, and use the remaining three as methyl radicals. We arrange them as follows: two at the second C atom, one at the third carbon. We call the resulting isomer: 2,2, 3 trimethylbutane.
Using heptane as an example, we examined how to correctly formulate isomers for saturated hydrocarbons. The photo shows examples of structural isomers for butene6 and its chlorine derivatives.
Alkenes
This class of organic substances has the general formula CnH2n. In addition to saturated C — C bonds, this class also has a double bond. It determines the basic properties of this series. Let's talk about how to leave isomers of alkenes. Let's try to identify their differences from saturated hydrocarbons. In addition to the main chain isomerism (structural formulas), representatives of this class of organic hydrocarbons are also characterized by three more types of isomers: geometric (cis and transform), multiple bond positions, and interclass isomerism (with cycloalkanes).
Isomers of C6H12
Let’s try to figure out how to compose the isomers of c6h12, given the fact that a substance with this formula can belong to two classes of organic substances: alkenes, cycloalkanes.
To begin with, let's think about how to compose 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 us try not only to compile the isomers of c6h12, but also to name the substances. This substance is hexene - 1. The number indicates the position in the double bond molecule. When moving along the carbon chain, we get hexene -2, as well as hexene - 3
Now we will discuss how to make isomers for this formula by changing the number of atoms in the main chain.
First, we shorten the carbon skeleton by one carbon atom, it will be considered as a methyl radical. We leave the double bond after the first atom C. The resulting isomer according to 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 branched unsaturated hydrocarbon is called 3 methylpentene -1.
One more isomer is possible without changing the main chain and the position of the double bond: 4 methylpentene -1.
For C6H12, you can try moving the double bond from the first to the second position without transforming the main chain itself. In this case, the radical will move along the carbon skeleton, starting from the second atom C. This isomer is called 2 methylpentene-2. In addition, the CH3 radical of the third carbon atom can be placed to obtain 3 methylpentene-2
If you place the radical at the fourth carbon of the atom in this chain, another new substance is formed, an unsaturated hydrocarbon with a meandering carbon skeleton - 4 methylpentene-2.
With a further reduction in the number C in the main chain, one more isomer can be obtained.
We leave the double bond after the first carbon atom, and put the two radicals on the third atom C of the main chain, we get 3.3 dimethylutene-1.
Now we place the radicals at the adjacent carbon atoms, without changing the position of the double bond, we obtain 2,3 dimethylbutene-1. Let’s try, without changing the size of the main chain, to move the double bond to the second position. In this case, we can deliver radicals only at 2 and 3 C atoms, having obtained 2,3 dimethylbutene-2.
There are no other structural isomers for this alkene; any attempts to invent them will lead to a violation of the theory of the structure of organic substances by A. M. Butlerov.
Spatial Isomers C6H12
Now we find out how to compose isomers and homologs from the point of view of spatial isomerism. It is important to understand that cis and alkene transformations are possible only for the double bond position 2 and 3.
When hydrocarbon radicals are in the same plane, cis is formed - measuring hexene -2, and when radicals are located in different planes, the trans form of hexene is 2.
Interclass isomers C6H12
In discussing how to compose isomers and homologues, one should not forget about such an option as interclass isomerism. For unsaturated hydrocarbons of a number of ethylene having the general formula CnH2n, cycloalkanes are such isomers. A feature of this class of hydrocarbons is the presence of a cyclic (closed) structure with saturated single bonds between carbon atoms. Formulas of cyclohexane, methylcyclopentane, dimethylcyclobutane, trimethylcyclopropane can be formulated.
Conclusion
Organic chemistry is multifaceted, mysterious. The amount of organic substances exceeds hundreds of times the number of inorganic compounds. This fact is easily explained by the existence of such a unique phenomenon as isomerism. If substances homogeneous in properties and structure are located in the same homological series, then when the position of carbon atoms in the chain changes, new compounds called isomers appear. Only after the appearance of the theory of the chemical structure of organic substances was it possible to classify all hydrocarbons, to understand the specifics of each class. One of the provisions of this theory is directly related to the phenomenon of isomerism. The great Russian chemist was able to understand, explain, prove that the chemical properties of a substance, its reaction activity, and practical application depend precisely on the location of carbon atoms. If we compare the number of isomers formed by saturated alkanes and unsaturated alkenes, alkenes are certainly in the lead. This is explained by the fact that in their molecules there is a double bond. Namely, it allows this class of organic substances to form not only alkenes of various types and structures, but also to talk about meclass isomerism with cycloalkanes.