By the first half of the 19th century, an enormous amount of factual material had been accumulated in organic chemistry, the further study of which was hampered by the lack of any systematizing basis. Starting from the 20s of the 19th century, successive theories began to appear, claiming to provide a generalized description of the structure of organic compounds. One of them was the theory of types, developed in the 1960s by the French scientist C. Gerard. According to this theory, all organic compounds were considered as derivatives of the simplest inorganic substances, taken as types.Sh. Gerard
Shortly before the appearance of the theory of the structure of A.M. Butlerov, the German chemist F.A. Kekule (1857) developed the theory of valency in relation to organic compounds, which established such facts as the tetravalency of the carbon atom and its ability to form carbon chains due to combination with carbon atoms.A. M. Butlerova F.A. Kekule
Theoretical developments of the pre-Butler period made a certain contribution to the knowledge of the structure of organic compounds. But none of the early theories was universal. And only A.M. Butlerov managed to create such a logically complete theory of structure, which to this day serves as the scientific basis of organic chemistry. Theory of the structure of A.M. Butlerov is based on a materialistic approach to a real molecule and proceeds from the possibility of knowing its structure experimentally. A.M. Butlerov attached fundamental importance to chemical reactions when establishing the structure of substances. Theory of the structure of A.M. Butlerova not only explained already known facts, her scientific significance lay in predicting the existence of new organic compounds. A.M. Butlerov A.M. Butlerova A.M. Butlerov A.M. Butlerov
Isomers are substances that have the same molecular formula, but different chemical structures, and therefore have different properties. Isomerism received a true explanation only in the second half of the 19th century on the basis of the theory of chemical structure by A.M. Butlerov (structural isomerism) and the stereochemical theory of Ya. G. Van't Hoff (spatial isomerism). Ya. G. van't Hoff
FormulaName Number of isomers CH 4 methane1 C4H6C4H6 ethane1 C3H8C3H8 propane1 C 4 H 10 butane2 C 5 H 12 pentane3 C 6 H 14 hexane5 C 7 H 16 heptane9 C 8 H 18 octane18 C 9 H 20 nonane35 C 10 H 22 decane75 C 11 H 24 undecane159 C 12 H 26 dodecane355 C 13 H 28 tridecane802 C 14 H 30 tetradecane1 858 C 15 H 32 pentadecane4 347 C 20 H 42 eicosane C 25 H 52 pentacosane C 30 H 62 triacontane C 40 H 82 tetracontane
Structural isomers are those that correspond to different structural formulas of organic compounds (with different orders of atoms). Spatial isomers have the same substituents on each carbon atom and differ only in their relative location in space.
Spatial isomers (stereoisomers). Stereoisomers can be divided into two types: geometric isomers and optical isomers. Geometric isomerism is characteristic of compounds containing a double bond or ring. In such molecules it is often possible to draw a conventional plane in such a way that the substituents on different carbon atoms can be on the same side (cis-) or on opposite sides (trans-) of this plane. If a change in the orientation of these substituents relative to the plane is possible only due to the breaking of one of the chemical bonds, then they speak of the presence of geometric isomers. Geometric isomers differ in their physical and chemical properties.
A new method for obtaining optical isomers of organic molecules has been discovered. When Alice found herself in her own, but “mirror” room, she was surprised: the room seemed similar, but still completely different. Mirror isomers of chemical molecules differ in the same way: they look similar, but behave differently. A critical area of organic chemistry is the separation and synthesis of these mirror variants. (Illustration by John Tenniel for Lewis Carroll's book "Alice Through the Looking Glass")
American scientists have learned to obtain optical isomers of aldehyde-based compounds, finally carrying out an important reaction that chemists have been working on for many years. In the experiment, they combined two catalysts operating on different principles. As a result of the combined action of these catalysts, two active organic molecules are formed, which combine to form the desired substance. Using this reaction as an example, the possibility of synthesizing a whole class of biologically important organic compounds is demonstrated.
At least 130 organic synthesis reactions are now known in which more or less pure chiral isomers are obtained. If the catalyst itself has chiral properties, then an optically active product will be obtained from an optically inactive substrate. This rule was derived at the beginning of the 20th century and remains basic today. The principle of selective action of a catalyst in relation to optical isomers is similar to a handshake: it is “convenient” for the catalyst to bind to only one of the chiral isomers, and therefore only one of the reactions is preferentially catalyzed. By the way, the term “chiral” comes from the Greek chéir hand.
Lesson content: Theories of the structure of organic compounds: prerequisites for their creation, basic principles. Chemical structure as the order of connection and mutual influence of atoms in molecules. Homology, isomerism. Dependence of the properties of substances on the chemical structure. Main directions of development of the theory of chemical structure. The dependence of the appearance of toxicity in organic compounds on the composition and structure of their molecules (the length of the carbon chain and the degree of its branching, the presence of multiple bonds, the formation of cycles and peroxide bridges, the presence of halogen atoms), as well as on the solubility and volatility of the compound.
Lesson objectives:
- Organize student activities to familiarize and initially consolidate the basic principles of the theory of chemical structure.
- Show students the universal nature of the theory of chemical structure using the example of inorganic isomers and the mutual influence of atoms in inorganic substances.
During the classes:
1. Organizational moment.
2. Updating students' knowledge.
1) What does organic chemistry study?
2) What substances are called isomers?
3) What substances are called homologues?
4) Name the theories known to you that arose in organic chemistry at the beginning of the 19th century.
5) What shortcomings did the theory of radicals have?
6) What shortcomings did type theory have?
3. Setting goals and objectives for the lesson.
The concept of valency formed an important part of A.M.’s theory of chemical structure. Butlerov in 1861
The periodic law formulated by D.I. Mendeleev in 1869, revealed the dependence of the valence of an element on its position in the periodic table.
The wide variety of organic substances that have the same qualitative and quantitative composition, but different properties, remained unclear. For example, about 80 different substances were known that corresponded to the composition C 6 H 12 O 2. Jens Jakob Berzelius proposed calling these substances isomers.
Scientists from many countries, with their work, have paved the way for the creation of a theory explaining the structure and properties of organic substances.
At a congress of German naturalists and doctors in the city of Speyer, a report was read entitled “Something in the chemical structure of bodies.” The author of the report was Kazan University professor Alexander Mikhailovich Butlerov. It was this very “something” that constituted the theory of chemical structure, which formed the basis of our modern ideas about chemical compounds.
Organic chemistry received a solid scientific basis, which ensured its rapid development in the next century until the present day. This theory made it possible to predict the existence of new compounds and their properties. The concept of chemical structure made it possible to explain such a mysterious phenomenon as isomerism.
The main principles of the theory of chemical structure are as follows:
1. Atoms in molecules of organic substances are combined in a certain sequence according to their valency.
2. The properties of substances are determined by the qualitative, quantitative composition, order of connection and mutual influence of atoms and groups of atoms in the molecule.
3. The structure of molecules can be established based on the study of their properties.
Let's consider these provisions in more detail. Molecules of organic substances contain atoms of carbon (valence IV), hydrogen (valence I), oxygen (valency II), nitrogen (valency III). Each carbon atom in molecules of organic substances forms four chemical bonds with other atoms, and carbon atoms can be connected in chains and rings. Based on the first principle of the theory of chemical structure, we will draw up structural formulas of organic substances. For example, it has been established that methane has the composition CH4. Taking into account the valences of carbon and hydrogen atoms, only one structural formula of methane can be proposed:
The chemical structure of other organic substances can be described by the following formulas:
ethanol
The second position of the theory of chemical structure describes the relationship known to us: composition - structure - properties. Let's see the manifestation of this pattern using the example of organic substances.
Ethane and ethyl alcohol have different qualitative compositions. The alcohol molecule, unlike ethane, contains an oxygen atom. How will this affect the properties?
The introduction of an oxygen atom into a molecule dramatically changes the physical properties of the substance. This confirms the dependence of properties on the qualitative composition.
Let's compare the composition and structure of the hydrocarbons methane, ethane, propane and butane.
Methane, ethane, propane and butane have the same qualitative composition, but different quantitative ones (the number of atoms of each element). According to the second position of the theory of chemical structure, they should have different properties.
| Substance | Boiling temperature,°C | Melting temperature,°C |
| CH 4 | – 182,5 | – 161,5 |
| C 2 H 6 | – 182,8 | – 88,6 |
| C 3 H 8 | – 187,6 | – 42,1 |
| C 4 H 10 | – 138,3 | – 0,5 |
As can be seen from the table, with an increase in the number of carbon atoms in a molecule, the boiling and melting temperatures increase, which confirms the dependence of the properties on the quantitative composition of the molecules.
The molecular formula C4H10 corresponds not only to butane, but also to its isomer isobutane:
Isomers have the same qualitative (carbon and hydrogen atoms) and quantitative (4 carbon atoms and ten hydrogen atoms) composition, but differ from each other in the order of connection of atoms (chemical structure). Let's see how the difference in the structure of isomers will affect their properties.
A branched hydrocarbon (isobutane) has higher boiling and melting points than a normal hydrocarbon (butane). This can be explained by the closer proximity of molecules to each other in butane, which increases the forces of intermolecular attraction and, therefore, requires more energy to separate them.
The third position of the theory of chemical structure shows the feedback between the composition, structure and properties of substances: composition - structure - properties. Let's consider this using the example of compounds with the composition C 2 H 6 O.
Let's imagine that we have samples of two substances with the same molecular formula C 2 H 6 O, which was determined through qualitative and quantitative analysis. But how can we find out the chemical structure of these substances? Studying their physical and chemical properties will help answer this question. When the first substance interacts with metallic sodium, the reaction does not occur, but the second actively interacts with it, releasing hydrogen. Let us determine the quantitative ratio of substances in the reaction. To do this, add a certain mass of sodium to the known mass of the second substance. Let's measure the volume of hydrogen. Let's calculate the amounts of substances. In this case, it turns out that from two moles of the substance under study, one mole of hydrogen is released. Therefore, each molecule of this substance is the source of one hydrogen atom. What conclusion can be drawn? Only one hydrogen atom differs in properties and, therefore, in structure (which atoms it is associated with) from all the others. Taking into account the valence of carbon, hydrogen and oxygen atoms, only one formula can be proposed for a given substance:
For the first substance, a formula can be proposed in which all hydrogen atoms have the same structure and properties:
A similar result can be obtained by studying the physical properties of these substances.
Thus, based on studying the properties of substances, we can draw a conclusion about its chemical structure.
The importance of the theory of chemical structure can hardly be overestimated. She armed chemists with a scientific basis for studying the structure and properties of organic substances. The Periodic Law formulated by D.I. has a similar meaning. Mendeleev. The theory of structure summarized all the scientific views prevailing in chemistry at that time. Scientists were able to explain the behavior of organic substances during chemical reactions. Based on the theory of A.M. Butlerov predicted the existence of isomers of some substances, which were later obtained. Just like the Periodic Law, the theory of chemical structure received its further development after the formation of the theory of atomic structure, chemical bonding and stereochemistry.
How science took shape at the beginning of the 19th century, when the Swedish scientist J. Ya. Berzelius first introduced the concept of organic substances and organic chemistry. The first theory in organic chemistry is the theory of radicals. Chemists discovered that during chemical transformations, groups of several atoms pass unchanged from a molecule of one substance to a molecule of another substance, just as atoms of elements pass from molecule to molecule. Such “immutable” groups of atoms are called radicals.
However, not all scientists agreed with the radical theory. Many generally rejected the idea of atomism - the idea of the complex structure of a molecule and the existence of an atom as its component part. What has been indisputably proven today and does not raise the slightest doubt, in the 19th century. was the subject of fierce controversy.
Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year; methodological recommendations; discussion programs Integrated LessonsChemical structure of a molecule represents its most characteristic and unique aspect, since it determines its general properties (mechanical, physical, chemical and biochemical). Any change in the chemical structure of a molecule entails a change in its properties. In the case of minor structural changes introduced into one molecule, small changes in its properties follow (usually affecting physical properties), but if the molecule has undergone profound structural changes, then its properties (especially chemical ones) will be profoundly changed.
For example, Alpha-aminopropionic acid (Alpha-alanine) has the following structure:
Alpha Alanine What we see:
- The presence of certain atoms (C, H, O, N),
- a certain number of atoms belonging to each class, which are bonded in a certain order;
All these design features determine a number of properties of Alpha-alanine, such as: solid state of aggregation, boiling point 295 ° C, solubility in water, optical activity, chemical properties of amino acids, etc.
When the amino group is bonded to another carbon atom (i.e., a minor structural change has occurred), which corresponds to beta-alanine:
Beta-alanine The general chemical properties still remain characteristic of amino acids, but the boiling point is already 200 ° C and there is no optical activity.
If, for example, two atoms in this molecule are connected by an N atom in the following order (deep structural change):
then the formed substance - 1-nitropropane, in its physical and chemical properties, is completely different from amino acids: 1-nitro-propane is a yellow liquid, with a boiling point of 131 ° C, insoluble in water.
Thus, structure-property relationship allows you to describe the general properties of a substance with a known structure and, conversely, allows you to find the chemical structure of a substance, knowing its general properties.
General principles of the theory of the structure of organic compounds
The essence of determining the structure of an organic compound is the following principles, which arise from the relationship between their structure and properties:
a) organic substances, in an analytically pure state, have the same composition, regardless of the method of their preparation;
b) organic substances, in an analytically pure state, have constant physical and chemical properties;
c) organic substances with constant composition and properties, have only one unique structure.
In 1861, the great Russian scientist A. M. Butlerov in his article “On the Chemical Structure of Matter” he revealed the main idea of the theory of chemical structure, which consists in the influence of the way the atoms in an organic substance are connected on its properties. He summarized all the knowledge and ideas available at that time about the structure of chemical compounds in the theory of the structure of organic compounds.
The main provisions of the theory of A. M. Butlerov
can be summarized as follows:
- In a molecule of an organic compound, the atoms are connected in a certain sequence, which determines its structure.
- The carbon atom in organic compounds has a valence of four.
- With the same composition of a molecule, several options for connecting the atoms of this molecule with each other are possible. Such compounds having the same composition but different structures were called isomers, and a similar phenomenon - isomerism.
- Knowing the structure of an organic compound, one can predict its properties; Knowing the properties of an organic compound, one can predict its structure.
- The atoms that form a molecule are subject to mutual influence, which determines their reactivity. Directly bonded atoms have a greater influence on each other, while the influence of atoms not directly bonded is much weaker.
Student A.M. Butlerova — V. V. Markovnikov continued to study the issue of mutual influence of atoms, which was reflected in 1869 in his dissertation work “Materials on the issue of mutual influence of atoms in chemical compounds.”
Credit to A.M. Butlerov and the importance of the theory of chemical structure is extremely great for chemical synthesis. The opportunity has opened up to predict the basic properties of organic compounds and to foresee the routes of their synthesis. Thanks to the theory of chemical structure, chemists first appreciated the molecule as an ordered system with a strict order of bonds between atoms. And at present, the main provisions of Butlerov’s theory, despite changes and clarifications, underlie modern theoretical concepts of organic chemistry.
Categories ,The first appeared at the beginning of the 19th century. radical theory(J. Gay-Lussac, F. Wehler, J. Liebig). Radicals are groups of atoms that pass without change during chemical reactions from one compound to another. This concept of radicals has been preserved, but most other provisions of the theory of radicals turned out to be incorrect.
According to type theories(C. Gerard) all organic substances can be divided into types corresponding to certain inorganic substances. For example, alcohols R-OH and ethers R-O-R were considered to be representatives of the water type H-OH, in which the hydrogen atoms are replaced by radicals. The theory of types created a classification of organic substances, some of the principles of which are used today.
The modern theory of the structure of organic compounds was created by the outstanding Russian scientist A.M. Butlerov.
Basic principles of the theory of the structure of organic compounds by A.M. Butlerov
1. Atoms in a molecule are arranged in a certain sequence according to their valency. The valency of the carbon atom in organic compounds is four.
2. The properties of substances depend not only on which atoms and in what quantities are included in the molecule, but also on the order in which they are connected to each other.
3. Atoms or groups of atoms that make up a molecule mutually influence each other, which determines the chemical activity and reactivity of the molecules.
4. Studying the properties of substances allows us to determine their chemical structure.
The mutual influence of neighboring atoms in molecules is the most important property of organic compounds. This influence is transmitted either through a chain of simple bonds or through a chain of conjugated (alternating) simple and double bonds.
Classification of organic compounds is based on the analysis of two aspects of the structure of molecules - the structure of the carbon skeleton and the presence of functional groups.
Organic compounds
Hydrocarbons Heterocyclic compounds
Limit- Unprecedent- Aroma-
efficient practical
Aliphatic Carbocyclic
Ultimate Unsaturated Ultimate Unsaturated Aromatic
(Alkanes) (Cycloalkanes) (Arenas)
WITH P H 2 P+2 C P H 2 P WITH P H 2 P -6
alkenes, polyenes and alkynes
WITH P H 2 P polyines C P H 2 P -2
Rice. 1. Classification of organic compounds according to the structure of the carbon skeleton
Classes of hydrocarbon derivatives based on the presence of functional groups:
Halogen derivatives R–Gal: CH 3 CH 2 Cl (chloroethane), C 6 H 5 Br (bromobenzene);
Alcohols and phenols R–OH: CH 3 CH 2 OH (ethanol), C 6 H 5 OH (phenol);
Thiols R–SH: CH 3 CH 2 SH (ethanethiol), C 6 H 5 SH (thiophenol);
Ethers R–O–R: CH 3 CH 2 –O–CH 2 CH 3 (diethyl ether),
complex R–CO–O–R: CH 3 CH 2 COOCH 2 CH 3 (ethyl acetic acid);
Carbonyl compounds: aldehydes R–CHO:
ketones R–СО–R: CH 3 COCH 3 (propanone), C 6 H 5 COCH 3 (methyl phenylketone);
Carboxylic acids R-COOH: (acetic acid), (benzoic acid)
Sulfonic acids R–SO 3 H: CH 3 SO 3 H (methanesulfonic acid), C 6 H 5 SO 3 H (benzenesulfonic acid)
Amines R–NH 2: CH 3 CH 2 NH 2 (ethylamine), CH 3 NHCH 3 (dimethylamine), C 6 H 5 NH 2 (aniline);
Nitro compounds R–NO 2 CH 3 CH 2 NO 2 (nitroethane), C 6 H 5 NO 2 (nitrobenzene);
Organometallic (organoelement) compounds: CH 3 CH 2 Na (ethyl sodium).
A series of compounds similar in structure, possessing similar chemical properties, in which individual members of the series differ from each other only in the number of -CH 2 - groups, is called homologous series, and the -CH 2 group is a homological difference . For members of a homologous series, the vast majority of reactions proceed in the same way (with the exception of only the first members of the series). Consequently, knowing the chemical reactions of only one member of the series, it can be stated with a high degree of probability that the same type of transformation occurs with the remaining members of the homologous series.
For any homologous series, a general formula can be derived that reflects the relationship between the carbon and hydrogen atoms of the members of this series; like this the formula is called general formula of the homologous series. Yes, S P H 2 P+2 – formula of alkanes, C P H 2 P+1 OH – aliphatic monohydric alcohols.
Nomenclature of organic compounds: trivial, rational and systematic nomenclature. Trivial nomenclature is a collection of historically established names. So, from the name it is immediately clear where malic, succinic or citric acid was isolated, how pyruvic acid was obtained (pyrolysis of grape acid), connoisseurs of the Greek language will easily guess that acetic acid is something sour, and glycerin is sweet. As new organic compounds were synthesized and the theory of their structure developed, other nomenclatures were created that reflected the structure of the compound (its belonging to a certain class).
Rational nomenclature constructs the name of a compound based on the structure of a simpler compound (the first member of a homologous series). CH 3 HE– carbinol, CH 3 CH 2 HE– methylcarbinol, CH 3 CH(OH) CH 3 – dimethylcarbinol, etc.
IUPAC nomenclature (systematic nomenclature). According to IUPAC (International Union of Pure and Applied Chemistry) nomenclature, the names of hydrocarbons and their functional derivatives are based on the name of the corresponding hydrocarbon with the addition of prefixes and suffixes inherent in this homologous series.
To correctly (and unambiguously) name an organic compound using systematic nomenclature, you must:
1) select the longest sequence of carbon atoms (parental structure) as the main carbon skeleton and give its name, paying attention to the degree of unsaturation of the compound;
2) identify All functional groups present in the compound;
3) establish which group is senior (see table), the name of this group is reflected in the name of the compound in the form of a suffix and it is placed at the end of the name of the compound; all other groups are given in the name in the form of prefixes;
4) number the carbon atoms of the main chain, giving the highest group the lowest number;
5) list the prefixes in alphabetical order (in this case, multiplying prefixes di-, tri-, tetra-, etc. are not taken into account);
6) write down the full name of the compound.
|
Connection class |
Functional group formula |
Suffix or ending |
|
|
Carboxylic acids |
Carboxy- |
Oic acid |
|
|
Sulfonic acids |
Sulfonic acid |
||
|
Aldehydes | |||
|
Hydroxy- | |||
|
Mercapto- | |||
|
С≡≡С | |||
|
Halogen derivatives |
Br, I, F, Cl |
Bromine-, iodine-, fluorine-, chlorine- |
-bromide, -iodide, -fluoride, -chloride |
|
Nitro compounds |
It is necessary to remember:
In the names of alcohols, aldehydes, ketones, carboxylic acids, amides, nitriles, acid halides, the suffix defining the class follows the suffix of the degree of unsaturation: for example, 2-butenal;
Compounds containing other functional groups are called hydrocarbon derivatives. The names of these functional groups are placed as prefixes before the name of the parent hydrocarbon: for example, 1-chloropropane.
The names of acidic functional groups, such as sulfonic acid or phosphinic acid, are placed after the name of the hydrocarbon skeleton: for example, benzenesulfonic acid.
Derivatives of aldehydes and ketones are often named after the parent carbonyl compound.
Esters of carboxylic acids are called derivatives of parent acids. The ending –oic acid is replaced by –oate: for example, methyl propionate is the methyl ester of propanoic acid.
To indicate that the substituent is bonded to the nitrogen atom of the parent structure, use a capital letter N before the name of the substituent: N-methylaniline.
Those. you need to start with the name of the parent structure, for which it is absolutely necessary to know by heart the names of the first 10 members of the homologous series of alkanes (methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane). You also need to know the names of the radicals formed from them - in this case, the ending -an changes to -il.
Consider a compound that is part of drugs used to treat eye diseases:
CH 3 – C(CH 3) = CH – CH 2 – CH 2 – C(CH 3) = CH – CHO
The basic parent structure is a chain of 8 carbon atoms, including an aldehyde group and both double bonds. Eight carbon atoms are octane. But there are 2 double bonds - between the second and third atoms and between the sixth and seventh. One double bond - the ending -an must be replaced with -ene, there are 2 double bonds, which means -diene, i.e. octadiene, and at the beginning we indicate their position, naming the atoms with lower numbers - 2,6-octadiene. We have dealt with the original structure and indefiniteness.
But the compound contains an aldehyde group, it is not a hydrocarbon, but an aldehyde, so we add the suffix -al, without a number, it is always the first - 2,6-octadienal.
Another 2 substituents are methyl radicals at the 3rd and 7th atoms. So, in the end we get: 3,7-dimethyl - 2,6-octadienal.