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>> Chemistry: Isomerism and its types
There are two types of isomerism: structural and spatial (stereoisomerism). Structural isomers differ from each other by the order of bonds of atoms in the molecule, stereo-isomers - by the arrangement of atoms in space with the same order of bonds between them.
The following types of structural isomerism are distinguished: isomerism of the carbon skeleton, positional isomerism, isomerism of various classes organic compounds(interclass isomerism).
Structural isomerism
Isomerism of the carbon skeleton is due to the different bond order between the carbon atoms forming the skeleton of the molecule. As has already been shown, the molecular formula C4H10 corresponds to two hydrocarbons: n-butane and isobutane. For the C5H12 hydrocarbon, three isomers are possible: pentane, iso-pentane and neopentane.
As the number of carbon atoms in a molecule increases, the number of isomers increases rapidly. For hydrocarbon C10H22 there are already 75 of them, and for hydrocarbon C20H44 - 366,319.
Positional isomerism is due to different position multiple bond, substituent, functional group with the same carbon skeleton of the molecule:
Isomerism of different classes of organic compounds (interclass isomerism) is due to different positions and combinations of atoms in the molecules of substances that have the same molecular formula, but belong to different classes. Thus, the molecular formula C6B12 corresponds to the unsaturated hydrocarbon hexene-1 and cyclic cyclohexane: 
Isomers of this type contain different functional groups and belong to different classes of substances. Therefore, they differ in physical and chemical properties much more than carbon skeleton isomers or positional isomers.
Spatial isomerism
Spatial isomerism is divided into two types: geometric and optical.
Geometric isomerism is characteristic of compounds containing double bonds and cyclic compounds. Since free rotation of atoms around a double bond or in a ring is impossible, the substituents can be located either on the same side of the plane of the double bond or ring (cis position) or on opposite sides (trans position). The designations cis and trans usually refer to a pair of identical substituents. 
Geometric isomers differ in physical and chemical properties.
Optical isomerism occurs when a molecule is incompatible with its image in a mirror. This is possible when the carbon atom in the molecule has four different substituents. This atom is called asymmetric. An example of such a molecule is the molecule α-aminopropionic acid (α-alanine) CH3CH(KH2)COOH.
As you can see, the a-alanine molecule cannot coincide with its mirror image no matter how it moves. Such spatial isomers are called mirror, optical antipodes, or enantiomers. All physical and almost all Chemical properties these isomers are identical.
The study of optical isomerism is necessary when considering many reactions occurring in the body. Most of these reactions occur under the action of enzymes - biological catalysts. The molecules of these substances must fit the molecules of the compounds on which they act, like a key to a lock; therefore, the spatial structure, the relative arrangement of sections of the molecules and other spatial factors play a role in the course of these reactions great importance. Such reactions are called stereoselective.
Most natural compounds are individual enantiomers, and their biological effects (from taste and smell to medicinal effects) differ sharply from the properties of their optical antipodes obtained in the laboratory. This difference in biological activity is of great importance, since it underlies most important property all living organisms - metabolism.
What types of isomerism do you know?
How does structural isomerism differ from spatial isomerism?
Which of the proposed connections are:
a) isomers;
b) homologues? 
Give all substances names.
4. Is geometric (cis-, trans) isomerism possible for: a) alkanes; b) alkenes; c) alkynes; d) cycloalkanes?
Explain, give examples. 
Isomers, isomerism
Isomers- these are substances that have the same qualitative and quantitative composition, but different structures and, therefore, different properties
The phenomenon of the existence of isomers is called isomerism
For example, a substance with the composition C 4 H 10 has two isomeric compounds.
The physical properties of butane and isobutane are different: isobutane has lower melting and boiling points than n.butane.
Ball-and-stick model of the butane molecule 
Ball-and-stick model of the isobutane molecule
The chemical properties of these isomers differ slightly, because they have the same qualitative composition and the nature of the bonds between the atoms in the molecule.
Another definition of isomers can be given as follows:
Isomers – substances that have the same molecular but different structural formulas.
Types of isomerism
Depending on the nature of the differences in the structure of the isomers, there are structural And spatial isomerism.
Structural isomers- connections of the same quality and quantitative composition, differing in the order of bonding of atoms, i.e. chemical structure.
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Structural isomerism is divided into: |
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1.Isomerism of the carbon skeleton |
2.Positional isomerism (multiple bond, functional group, substituent) |
3.Interclass isomerism CH 3 -CH 2 -NO 2 nitroethane HOOC-CH 2 -NH 2 aminoacetic acid (glycine) |
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Position isomerism |
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multiple connection CH 2 = CH-CH = CH 2 CH 3 -CH= C= CH 2 |
functional group CH 3 -CHON -CH 3 CH 2 OH -CH 2 -CH 3 |
Deputy CH 3 -CHCI -CH 3 CH 2 CI -CH 2 -CH 3 |
Structural isomerism
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Isomerism of the position of a multiple (double) bond: Butene-1 and butene-2 |
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Carbon skeleton isomerism: Cyclobutane and methylcyclopropane |
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Interclass isomerism: Butene and cyclobutane |
Spatial isomers (stereoisomers) with the same composition and the same chemical structure, they differ in the spatial arrangement of atoms in the molecule
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Spatial isomerism is divided into: |
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Characteristic of substances containing double bonds or cyclic ones. |
Optical isomers are also called mirror or chiral (like left and right hand)
In this article we will talk about structural isomers, features of their structure and types of isomerism. We will analyze in detail the phenomenon of isomerism itself, and will also provide examples of their use in life.
The phenomenon of isomerism
Isomerism is a special phenomenon that predetermines the existence of chemicals. compounds, those same isomers, substances with identical atomic compositions and molecular weights, differing only in the atomic arrangement in space or in their structure, which leads to a change and acquisition of different, new properties. Structural isomers are substances formed as a result of such a change in the position of their atoms in space, which will be discussed in more detail below.
Speaking about isomerism, it is worth remembering the existence of such a process as isomerization, which is the process of transition of one isomer to another as a result of chemical reactions. transformations.
Types of isomerism
Valence isomerism is a type of structure of isomers in which the transfer of the isomers themselves (one to another) is possible as a result of the redistribution of valence bonds.
Positional isomerism is a type of substance with an identical carbon skeleton but a different position of the functional groups. A striking example is the 2- and 4-acids of chlorobutane.
Interclass isomerism conceals its difference between isomers in the nature of the functional groups.
Metamerism is the distribution of the position of carbon atoms between a certain number of carbon radicals, the heteroatom of the molecule serving as a separator. This type of isomerism is typical for amines, thioalcohols, and ethers, both simple and complex.
Isomerism of the carbon skeleton is the difference in the position of carbon atoms, or rather their order. For example: phenanthrene and anthracene have a common formula C14H10, but a different type of redistribution of valence bonds.
Structural isomers
Structural isomers are substances that have a similar formula of the structure of the substance, but differ in the formula of the molecule. Structural isomers are those that are identical to each other in quantitative and qualitative composition, but the order of atomic bonding ( chemical structure) has differences.
Structural isomers are classified according to the type of isometric structure, the types of which are given above in the paragraph on the types of isomerism.
The structural formula of the isomer of the substance has a wide range of modifications. Some examples of isomerism are substances such as butanoic acid, 2-methylpropanoic acid, methyl propionate, dioxane, ethyl acetate, isopropyl formate, which have the same composition of all three types of atoms in the substance, but differ in the position of the atoms in the compound itself.
Another striking example of isomerism is the existence of pentane, neopentane and isopentane.
Names of isomers
As mentioned earlier, structural isomers are substances that have a similar formula in the structure of the substance, but differ in the formula of the molecule. Such compounds have a classification that corresponds to the characteristics of their properties, the structure and position of atoms in the isomer molecule, differences in the number of functional groups, valence bonds, the presence of atoms of a certain element in the substance, etc. The names of structural isomers are obtained in various ways. Let's consider this using the example of 3-methylbutanol 1, as a representative of alcohols.
In the case of alcohols, when obtaining the name of alcohols, everything begins with the selection of the carbon chain, which is dominant, and numbering is carried out, the purpose of which is to assign the OH group the smallest possible number, taking into account the order. The name itself begins with a substituent in the carbon chain, then the name of the main chain follows, and then the suffix -ol is added, and the number indicates the carbon atom associated with the OH group.
ἴσος - equal + μέρος - share, part) - a phenomenon consisting in the existence of chemical compounds - isomers, - identical in atomic composition and molecular weight, but differing in structure or arrangement of atoms in space and, as a result, in properties.Encyclopedic YouTube
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This type of isomerism is divided into enantiomerism(optical isomerism) and diastereomerism.
Enantiomerism (optical isomerism)
The process of interconversion of enantiomers is called racemization: it leads to the disappearance of optical activity as a result of the formation of an equimolar mixture of (−)- and (+)-forms, that is, the racemate. The interconversion of diastereomers leads to the formation of a mixture in which the thermodynamically more stable form. In the case of π-diastereomers, this is usually the trans form. The interconversion of conformational isomers is called conformational equilibrium.
The phenomenon of isomerism greatly contributes to the growth in the number of known (and, to an even greater extent, the number of potentially possible) compounds. Thus, the possible number of structural isomeric decyl alcohols is more than 500 (about 70 of them are known), and there are more than 1500 spatial isomers.
In the theoretical consideration of problems of isomerism, topological methods are becoming increasingly widespread; Mathematical formulas have been derived to calculate the number of isomers.