Prerequisites for the creation of the theory of organic compounds. The main provisions of the theory of the chemical structure of organic compounds by A.M. Butlerov

Lecture 15

Theory of the structure of organic substances. Main classes of organic compounds.

Organic chemistry - the science that studies organic matter. Otherwise, it can be defined as chemistry of carbon compounds. The latter occupies a special place in the periodic system of D.I. Mendeleev in terms of the variety of compounds, of which about 15 million are known, while the number of inorganic compounds is five hundred thousand. Organic substances have been known to mankind for a long time as sugar, vegetable and animal fats, coloring, fragrant and medicinal substances. Gradually, people learned to process these substances to obtain a variety of valuable organic products: wine, vinegar, soap, etc. Advances in organic chemistry are based on achievements in the field of chemistry of proteins, nucleic acids, vitamins, etc. Organic chemistry is of great importance for the development of medicine, since the vast majority of drugs are organic compounds not only of natural origin, but also obtained mainly by synthesis. Exceptional value wandered macromolecular organic compounds (synthetic resins, plastics, fibers, synthetic rubbers, dyes, herbicides, insecticides, fungicides, defoliants…). The importance of organic chemistry for the production of food and industrial goods is enormous.

Modern organic chemistry has penetrated deeply into the chemical processes that occur during the storage and processing of food products: the processes of drying, rancidity and saponification of oils, fermentation, baking, pickling, obtaining drinks, in the production of dairy products, etc. The discovery and study of enzymes, perfumes and cosmetics also played an important role.

One of the reasons for the great variety of organic compounds is the peculiarity of their structure, which is manifested in the formation of covalent bonds and chains by carbon atoms, different in type and length. The number of bonded carbon atoms in them can reach tens of thousands, and the configuration of carbon chains can be linear or cyclic. In addition to carbon atoms, the chain can include oxygen, nitrogen, sulfur, phosphorus, arsenic, silicon, tin, lead, titanium, iron, etc.

The manifestation of these properties by carbon is associated with several reasons. It has been confirmed that the energies of the C–C and C–O bonds are comparable. Carbon has the ability to form three types of hybridization of orbitals: four sp 3 - hybrid orbitals, their orientation in space is tetrahedral and corresponds to simple covalent bonds; three hybrid sp 2 - orbitals located in the same plane, in combination with a non-hybrid orbital form double multiples connections (─С = С─); also with the help of sp - hybrid orbitals of linear orientation and non-hybrid orbitals between carbon atoms arise triple multiples bonds (─ C ≡ C ─). At the same time, these types of bonds form carbon atoms not only with each other, but also with other elements. Thus, the modern theory of the structure of matter explains not only a significant number of organic compounds, but also the influence of their chemical structure on properties.

It also fully confirms the fundamentals theories of chemical structure, developed by the great Russian scientist A.M. Butlerov. ITS main provisions:

1) in organic molecules, atoms are connected to each other in a certain order according to their valency, which determines the structure of the molecules;

2) the properties of organic compounds depend on the nature and number of their constituent atoms, as well as on the chemical structure of molecules;

3) each chemical formula corresponds to a certain number of possible isomer structures;

4) each organic compound has one formula and has certain properties;

5) in molecules there is a mutual influence of atoms on each other.

Classes of organic compounds

According to the theory, organic compounds are divided into two series - acyclic and cyclic compounds.

1. Acyclic compounds.(alkanes, alkenes) contain an open, open carbon chain - straight or branched:

N N N N N N

│ │ │ │ │ │ │

N─ S─S─S─S─ N N─S─S─S─N

│ │ │ │ │ │ │

N N N N N │ N

Normal butane isobutane (methyl propane)

2. a) Alicyclic compounds- compounds that have closed (cyclic) carbon chains in molecules:

cyclobutane cyclohexane

b) Aromatic compounds, in the molecules of which there is a benzene skeleton - a six-membered cycle with alternating single and double bonds (arenes):

c) Heterocyclic compounds- cyclic compounds containing, in addition to carbon atoms, nitrogen, sulfur, oxygen, phosphorus and some trace elements, which are called heteroatoms.

furan pyrrole pyridine

In each row, organic substances are divided into classes - hydrocarbons, alcohols, aldehydes, ketones, acids, esters, in accordance with the nature of the functional groups of their molecules.

There is also a classification according to the degree of saturation and functional groups. According to the degree of saturation, they distinguish:

1. Limit saturated There are only single bonds in the carbon skeleton.

─С─С─С─

2. Unsaturated unsaturated– there are multiple (=, ≡) bonds in the carbon skeleton.

─С=С─ ─С≡С─

3. aromatic– unlimiting cycles with ring conjugation of (4n + 2) π-electrons.

By functional groups

1. Alcohols R-CH 2 OH

2. Phenols

3. Aldehydes R─COH Ketones R─C─R

4. Carboxylic acids R─COOH О

5. Esters R─COOR 1

The largest event in the development of organic chemistry was the creation in 1961 by the great Russian scientist A.M. Butlerov theory of the chemical structure of organic compounds.

Before A.M. Butlerov, it was considered impossible to know the structure of the molecule, that is, the order of the chemical bond between atoms. Many scientists even denied the reality of atoms and molecules.

A.M. Butlerov refuted this opinion. He started from the right materialistic and philosophical ideas about the reality of the existence of atoms and molecules, about the possibility of knowing the chemical bond of atoms in a molecule. He showed that the structure of a molecule can be established empirically by studying the chemical transformations of a substance. Conversely, knowing the structure of the molecule, one can derive the chemical properties of the compound.

The theory of chemical structure explains the diversity of organic compounds. It is due to the ability of tetravalent carbon to form carbon chains and rings, combine with atoms of other elements and the presence of isomerism in the chemical structure of organic compounds. This theory laid the scientific foundations of organic chemistry and explained its most important regularities. The basic principles of his theory A.M. Butlerov stated in the report "On the theory of chemical structure".

The main provisions of the theory of structure are as follows:

1) in molecules, atoms are connected to each other in a certain sequence in accordance with their valency. The bonding order of atoms is called chemical structure;

2) the properties of a substance depend not only on which atoms and in what quantity are part of its molecule, but also on the order in which they are interconnected, that is, on the chemical structure of the molecule;

3) atoms or groups of atoms that formed a molecule mutually influence each other.

In the theory of chemical structure, much attention is paid to the mutual influence of atoms and groups of atoms in a molecule.

Chemical formulas that show the order in which atoms are combined in molecules are called structural formulas or building formulas.

The value of the theory of chemical structure of A.M. Butlerov:

1) is an essential part of the theoretical foundation of organic chemistry;

2) in importance it can be compared with the Periodic system of elements of D.I. Mendeleev;

3) it made it possible to systematize a huge amount of practical material;

4) made it possible to predict in advance the existence of new substances, as well as indicate ways to obtain them.

The theory of chemical structure serves as the guiding basis in all research in organic chemistry.

12 Phenols, hydroxy derivatives aromatic compounds containing one or more hydroxyl groups (–OH) attached to the carbon atoms of the aromatic nucleus. By the number of OH groups, monoatomic phosphorus is distinguished, for example, oxybenzene C 6 H 5 OH, usually called simply phenol, oxytoluenes CH 3 C 6 H 4 OH - the so-called cresols, oxynaphthalenes - naphthols, diatomic, for example dioxybenzenes C 6 H 4 (OH) 2 ( hydroquinone, pyrocatechin, resorcinol), polyatomic, for example pyrogallol, phloroglucinol. F. - colorless crystals with a characteristic odor, less often liquids; well soluble in organic solvents (alcohol, ether, oenzol). Possessing acidic properties, F. form salt-like products - phenolates: ArOH + NaOH (ArONa + H 2 O (Ar is an aromatic radical). Alkylation and acylation of phenolates leads to F. esters - simple ArOR and complex ArOCOR (R - organic radical). Esters can be obtained by the direct interaction of phosphorus with carboxylic acids, their anhydrides, and acid chlorides.When phenols are heated with CO 2, phenolic acids are formed, for example salicylic acid. Unlike alcohols, the hydroxyl group F. with great difficulty is replaced by a halogen. Electrophilic substitution in the F.'s core (halogenation, nitration, sulfonation, alkylation, etc.) is carried out much more easily than in unsubstituted aromatic hydrocarbons; replacement groups are sent to ortho- And pair-positions to the OH group (see. Rule orientations). Catalytic hydrogenation of F. leads to alicyclic alcohols, for example, C 6 H 5 OH is reduced to cyclohexanol. F. is also characterized by condensation reactions, for example, with aldehydes and ketones, which is used in industry to obtain phenol- and resorcinol-formaldehyde resins, diphenylolpropane, and other important products.

F. is obtained, for example, by hydrolysis of the corresponding halogen derivatives, alkaline melting of arylsulfonic acids ArSO 2 OH, isolated from coal tar, brown coal tar, etc. F. is an important raw material in the production of various polymers, adhesives, paints and varnishes, dyes, and drugs ( phenolphthalein, salicylic acid, salol), surfactants and fragrances. Some F. are used as antiseptics and antioxidants (for example, polymers, lubricating oils). For the qualitative identification of F., solutions of ferric chloride are used, which form colored products with F.. F. toxic (see. Wastewater.).

13 Alkanes

general characteristics

Hydrocarbons are the simplest organic compounds, consisting of two elements: carbon and hydrogen. Limit hydrocarbons, or alkanes (international name), are compounds whose composition is expressed by the general formula C n H 2n + 2, where n is the number of carbon atoms. In molecules of saturated hydrocarbons, carbon atoms are interconnected by a simple (single) bond, and all other valences are saturated with hydrogen atoms. Alkanes are also called saturated hydrocarbons or paraffins (The term "paraffins" means "having a low affinity").

The first member of the homologous series of alkanes is methane CH 4 . The ending -an is typical for the names of saturated hydrocarbons. This is followed by ethane C 2 H 6, propane C 3 H 8, butane C 4 H 10. Starting from the fifth hydrocarbon, the name is formed from the Greek numeral, indicating the number of carbon atoms in the molecule, and the ending -an. These are C 5 H 12 pentane, C 6 H 14 hexane, C 7 H 16 heptane, C 8 H 18 octane, C 9 H 20 nonane, C 10 H 22 decane, etc.

In the homologous series, a gradual change in the physical properties of hydrocarbons is observed: the boiling and melting points increase, and the density increases. Under normal conditions (temperature ~ 22 ° C), the first four members of the series (methane, ethane, propane, butane) are gases, C 5 H 12 to C 16 H 34 are liquids, and C 17 H 36 are solids.

Alkanes, starting from the fourth member of the series (butane), have isomers.

All alkanes are saturated with hydrogen to the limit (maximum). Their carbon atoms are in a state of sp 3 hybridization, which means they have simple (single) bonds.

Nomenclature

The names of the first ten members of the series of saturated hydrocarbons have already been given. To emphasize that an alkane has an unbranched carbon chain, the word normal (n-) is often added to the name, for example:

CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3

n-butane n-heptane

(normal butane) (normal heptane)

When a hydrogen atom is detached from an alkane molecule, one-valve particles are formed, called hydrocarbon radicals (abbreviated as R). The names of monovalent radicals are derived from the names of the corresponding hydrocarbons with the ending –an replaced by -yl. Here are the relevant examples:

Radicals are formed not only by organic but also by inorganic compounds. So, if we take away the hydroxyl group OH from nitric acid, then we get a monovalent radical - NO 2, called a nitro group, etc.

When two hydrogen atoms are removed from a hydrocarbon molecule, divalent radicals are obtained. Their names are also derived from the names of the corresponding saturated hydrocarbons with the ending -an replaced by -ylidene (if the hydrogen atoms are detached from one carbon atom) or -ylene (if the hydrogen atoms are detached from two adjacent carbon atoms). The CH 2 = radical is called methylene.

The names of radicals are used in the nomenclature of many derivatives of hydrocarbons. For example: CH 3 I - methyl iodide, C 4 H 9 Cl - butyl chloride, CH 2 Cl 2 - methylene chloride, C 2 H 4 Br 2 - ethylene bromide (if bromine atoms are bonded to different carbon atoms) or ethylidene bromide (if bromine atoms are bonded to one carbon atom).

Two nomenclatures are widely used for the name of isomers: the old - rational and modern - substitution, which is also called systematic or international (proposed by the International Union of Pure and Applied Chemistry IUPAC).

According to rational nomenclature, hydrocarbons are considered as derivatives of methane, in which one or more hydrogen atoms are replaced by radicals. If the same radicals are repeated several times in the formula, then they are indicated by Greek numerals: di - two, three - three, tetra - four, penta - five, hexa - six, etc. For example:

Rational nomenclature is convenient for not very complex connections.

According to substitutional nomenclature, the name is based on one carbon chain, and all other fragments of the molecule are considered as substituents. In this case, the longest chain of carbon atoms is chosen, and the chain atoms are numbered from the end closest to the hydrocarbon radical. Then they name: 1) the number of the carbon atom to which the radical is associated (starting with the simplest radical); 2) hydrocarbon, which corresponds to a long chain. If the formula contains several identical radicals, then before their name indicate the number in words (di-, tri-, tetra-, etc.), and the numbers of the radicals are separated by commas. Here is how hexane isomers should be named according to this nomenclature:

Here's a more complex example:

Both substitutional and rational nomenclature are used not only for hydrocarbons, but also for other classes of organic compounds. For some organic compounds, historically established (empirical) or so-called trivial names are used (formic acid, sulfuric ether, urea, etc.).

When writing the formulas of isomers, it is easy to notice that the carbon atoms occupy an unequal position in them. A carbon atom that is connected to only one carbon atom in the chain is called primary, with two - secondary, with three - tertiary, with four - Quaternary. So, for example, in the last example, carbon atoms 1 and 7 are primary, 4 and 6 are secondary, 2 and 3 are tertiary, 5 is quaternary. The properties of hydrogen atoms, other atoms, and functional groups depend on which carbon atom they are associated with: primary, secondary, or tertiary. This must always be taken into account.

Receipt. Properties.

physical properties. Under normal conditions, the first four members of the homologous series of alkanes (C 1 - C 4) are gases. Normal alkanes from pentane to heptadecane (C 5 - C 17) are liquids, starting from C 18 and above are solids. As the number of carbon atoms in the chain increases, i.e. with an increase in the relative molecular weight, the boiling and melting points of alkanes increase. With the same number of carbon atoms in a molecule, branched alkanes have lower boiling points than normal alkanes.

Alkanes are practically insoluble in water, since their molecules are low-polar and do not interact with water molecules, they dissolve well in non-polar organic solvents such as benzene, carbon tetrachloride, etc. Liquid alkanes mix easily with each other.

The main natural sources of alkanes are oil and natural gas. Various oil fractions contain alkanes from C 5 H 12 to C 30 H 62 . Natural gas consists of methane (95%) with an admixture of ethane and propane.

Of the synthetic methods for obtaining alkanes, the following can be distinguished:

1. Obtaining from unsaturated hydrocarbons. The interaction of alkenes or alkynes with hydrogen ("hydrogenation") occurs in the presence of metal catalysts (Ni, Pd) at
heating:

CH s -C≡CH + 2H 2 → CH 3 -CH 2 -CH 3.

2. Obtaining from halogenated. When monohalogenated alkanes are heated with sodium metal, alkanes with twice the number of carbon atoms are obtained (Wurtz reaction):

C 2 H 5 Br + 2Na + Br-C 2 H 5 → C 2 H 5 -C 2 H 5 + 2NaBr.

A similar reaction is not carried out with two different halogen-substituted alkanes, since this produces a mixture of three different alkanes

3. Obtaining from salts of carboxylic acids. When anhydrous salts of carboxylic acids are fused with alkalis, alkanes are obtained containing one less carbon atom compared to the carbon chain of the original carboxylic acids:

4. Obtaining methane. In an electric arc burning in a hydrogen atmosphere, a significant amount of methane is formed:

C + 2H 2 → CH 4.

The same reaction occurs when carbon is heated in a hydrogen atmosphere to 400–500°C at elevated pressure in the presence of a catalyst.

In laboratory conditions, methane is often obtained from aluminum carbide:

Al 4 C 3 + 12H 2 O \u003d ZSN 4 + 4Al (OH) 3.

Chemical properties. Under normal conditions, alkanes are chemically inert. They are resistant to the action of many reagents: they do not interact with concentrated sulfuric and nitric acids, with concentrated and molten alkalis, they are not oxidized by strong oxidizing agents - potassium permanganate KMnO 4, etc.

The chemical stability of alkanes is explained by the high strength of C-C and C-H s-bonds, as well as their non-polarity. Nonpolar C-C and C-H bonds in alkanes are not prone to ionic cleavage, but are capable of cleaving homolytically under the action of active free radicals. Therefore, alkanes are characterized by radical reactions, as a result of which compounds are obtained where hydrogen atoms are replaced by other atoms or groups of atoms. Therefore, alkanes enter into reactions proceeding according to the mechanism of radical substitution, denoted by the symbol S R (from English, substitution radicalic). According to this mechanism, hydrogen atoms are most easily replaced at tertiary, then at secondary and primary carbon atoms.

1. Halogenation. When alkanes interact with halogens (chlorine and bromine) under the action of UV radiation or high temperature, a mixture of products from mono- to polyhalogen-substituted alkanes is formed. The general scheme of this reaction is shown using methane as an example:

b) Chain growth. The chlorine radical takes away a hydrogen atom from the alkane molecule:

Cl + CH 4 → HCl + CH 3

In this case, an alkyl radical is formed, which takes away the chlorine atom from the chlorine molecule:

CH 3 + Cl 2 → CH 3 Cl + Cl

These reactions are repeated until chain termination occurs in one of the following reactions:

Cl + Cl → Cl 2, CH 3 + CH 3 → C 2 H 6, CH 3 + Cl → CH 3 Cl

Overall reaction equation:

In radical reactions (halogenation, nitration), first of all, hydrogen atoms are mixed at the tertiary, then at the secondary and primary carbon atoms. This is explained by the fact that the bond of the tertiary carbon atom with hydrogen is most easily broken homolytically (bond energy 376 kJ/mol), then the secondary one (390 kJ/mol) and only then the primary one (415 kJ/mol).

3. Isomerization. Normal alkanes can be converted to branched-chain alkanes under certain conditions:

4. Cracking is a hemolytic rupture of C-C bonds, which occurs when heated and under the action of catalysts.
When higher alkanes are cracked, alkenes and lower alkanes are formed; when methane and ethane are cracked, acetylene is formed:

C 8 H 18 → C 4 H 10 + C 4 H 8,

2CH 4 → C 2 H 2 + ZH 2,

C 2 H 6 → C 2 H 2 + 2H 2.

These reactions are of great industrial importance. In this way, high-boiling oil fractions (fuel oil) are converted into gasoline, kerosene and other valuable products.

5. Oxidation. With the mild oxidation of methane with atmospheric oxygen in the presence of various catalysts, methyl alcohol, formaldehyde, and formic acid can be obtained:

Soft catalytic oxidation of butane with atmospheric oxygen is one of the industrial methods for producing acetic acid:

t°
2C 4 H 10 + 5O 2 → 4CH 3 COOH + 2H 2 O.
cat

In air, alkanes burn to CO 2 and H 2 O:

C n H 2n + 2 + (Zn + 1) / 2O 2 \u003d nCO 2 + (n + 1) H 2 O.

Alkenes

Alkenes (otherwise olefins or ethylene hydrocarbons) are acyclic unsaturated hydrocarbons containing one double bond between carbon atoms, forming a homologous series with the general formula CnH2n. Carbon atoms in a double bond are in a state of sp² hybridization.

The simplest alkene is ethene (C2H4). According to the IUPAC nomenclature, the names of alkenes are formed from the names of the corresponding alkanes by replacing the suffix "-an" with "-en"; the position of the double bond is indicated by an Arabic numeral.

homologous series

Alkenes with more than three carbon atoms have isomers. Alkenes are characterized by isomerism of the carbon skeleton, double bond positions, interclass and geometric.

ethene	C2H4
propene	C3H6
n-butene	C4H8
n-pentene	C5H10
n-hexene	C6H12
n-heptene	C7H14
n-octene	C8H16
n-nonene	C9H18
n-decene	C10H20

Physical properties

Melting and boiling points increase with molecular weight and length of the main carbon chain.
Under normal conditions, alkenes from C2H4 to C4H8 are gases; from C5H10 to C17H34 - liquids, after C18H36 - solids. Alkenes are insoluble in water, but readily soluble in organic solvents.

Chemical properties

Alkenes are chemically active. Their chemical properties are determined by the presence of a double bond.
Ozonolysis: The alkene is oxidized to aldehydes (in the case of monosubstituted vicinal carbons), ketones (in the case of disubstituted vicinal carbons), or a mixture of aldehyde and ketone (in the case of a tri-substituted alkene on the double bond):

R1–CH=CH–R2 + O3 → R1–C(H)=O + R2C(H)=O + H2O
R1–C(R2)=C(R3)–R4+ O3 → R1–C(R2)=O + R3–C(R4)=O + H2O
R1–C(R2)=CH–R3+ O3 → R1–C(R2)=O + R3–C(H)=O + H2O

Ozonolysis under severe conditions - the alkene is oxidized to an acid:

R"–CH=CH–R" + O3 → R"–COOH + R"–COOH + H2O

Double bond attachment:
CH2=CH2 +Br2 → CH2Br-CH2Br

Oxidation with peracids:
CH2=CH2 + CH3COOOOH →
or
CH2=CH2 + HCOOH → HOCH2CH2OH

slide 1>

Lecture objectives:

• Educational:
  • to form concepts about the essence of the theory of the chemical structure of organic substances, based on the knowledge of students about the electronic structure of atoms of elements, their position in the Periodic system of D.I. Mendeleev, on the degree of oxidation, the nature of the chemical bond, and other major theoretical provisions:
    • the sequence of carbon atoms in the chain,
    • mutual influence of atoms in a molecule,
    • dependence of the properties of organic substances on the structure of molecules;
  • form an idea of ​​the development of theories in organic chemistry;
  • learn the concepts: isomers and isomerism;
  • explain the meaning of the structural formulas of organic substances and their advantages over molecular ones;
  • show the necessity and prerequisites for the creation of a theory of chemical structure;
  • Continue developing your writing skills.
• Educational:
  • develop mental techniques of analysis, comparison, generalization;
  • develop abstract thinking;
  • to train the attention of students in the perception of a large amount of material;
  • develop the ability to analyze information and highlight the most important material.
• Educational:
  • for the purpose of patriotic and international education, provide students with historical information about the life and work of scientists.

DURING THE CLASSES

1. Organizational part

- Greetings
- Preparing students for the lesson
- Obtaining information about absentees.

2. Learning new things

Lecture plan:<Annex 1 . Slide 2>

I. Prestructural theories:
- vitalism;
– the theory of radicals;
- type theory.
II. Brief information about the state of chemical science by the 60s of the XIX century. Conditions for creating a theory of the chemical structure of substances:
- the need to create a theory;
- prerequisites for the theory of chemical structure.
III. The essence of the theory of the chemical structure of organic substances A.M. Butlerov. The concept of isomerism and isomers.
IV. The value of the theory of the chemical structure of organic substances A.M. Butlerov and its development.

3. Homework: synopsis, p. 2.

4. Lecture

I. Knowledge about organic substances has been accumulating gradually since ancient times, but as an independent science, organic chemistry arose only at the beginning of the 19th century. Registration of independence of org.chemistry is associated with the name of the Swedish scientist J. Berzelius<Annex 1 . Slide 3>. In 1808-1812. he published his large manual on chemistry, in which he originally intended to consider, along with mineral substances, also substances of animal and plant origin. But the part of the textbook devoted to organic substances appeared only in 1827.
J. Berzelius saw the most significant difference between inorganic and organic substances in that the former can be obtained synthetically in laboratories, while the latter are allegedly formed only in living organisms under the influence of a certain “life force” - a chemical synonym for “soul”, "spirit", "divine origin" of living organisms and their constituent organic substances.
The theory that explained the formation of organic compounds by the intervention of "life force" was called vitalism. She has been popular for some time. In the laboratory, it was possible to synthesize only the simplest carbon-containing substances, such as carbon dioxide - CO 2, calcium carbide - CaC 2, potassium cyanide - KCN.
Only in 1828 did the German scientist Wöhler<Annex 1 . Slide 4> managed to obtain the organic substance urea from an inorganic salt - ammonium cyanate - NH 4 CNO.
NH 4 CNO -– t –> CO (NH 2) 2
In 1854 the French scientist Berthelot<Annex 1 . Slide 5>Received triglyceride. This led to the need to change the definition of organic chemistry.
Scientists tried to unravel the nature of the molecules of organic substances based on the composition and properties, sought to create a system that would make it possible to link together the disparate facts that had accumulated by the beginning of the 19th century.
The first attempt to create a theory that sought to generalize the data available on organic substances is associated with the name of the French chemist J. Dumas<Annex 1 . Slide 6>. It was an attempt to consider from a unified point of view a fairly large group of org. compounds, which today we would call ethylene derivatives. Organic compounds turned out to be derivatives of some radical C 2 H 4 - etherine:
C 2 H 4 * HCl - ethyl chloride (etherine hydrochloride)
The idea embedded in this theory - an approach to organic matter as consisting of 2 parts - later formed the basis of a broader theory of radicals (J. Berzelius, J. Liebig, F. Wöhler). This theory is based on the notion of a "dualistic structure" of substances. J. Berzelius wrote: "Each organic substance consists of 2 components that carry the opposite electric charge." One of these components, namely the electronegative part, J. Berzelius considered oxygen, while the rest, actually organic, should have been an electropositive radical.

The main provisions of the theory of radicals:<Annex 1 . Slide 7>

- the composition of organic substances includes radicals that carry a positive charge;
- radicals are always constant, do not undergo changes, they pass without changes from one molecule to another;
- radicals can exist in free form.

Gradually science accumulated facts that contradicted the theory of radicals. So J. Dumas carried out the replacement of hydrogen with chlorine in hydrocarbon radicals. Scientists, adherents of the theory of radicals, it seemed incredible that chlorine, charged negatively, played the role of hydrogen, positively charged in compounds. In 1834, J. Dumas was given the task of investigating an unpleasant incident during a ball in the palace of the French king: candles emitted suffocating smoke when burned. J. Dumas found that the wax from which the candles were made was treated with chlorine for bleaching. At the same time, chlorine entered the wax molecule, replacing part of the hydrogen contained in it. The suffocating fumes that frightened the royal guests turned out to be hydrogen chloride (HCl). Later, J. Dumas received trichloroacetic acid from acetic acid.
Thus, the electropositive hydrogen was replaced by the extremely electronegative element chlorine, while the properties of the compound remained almost unchanged. Then J. Dumas concluded that the dualistic approach should be replaced by an approach to the organizational connection as a whole.

The radical theory was gradually abandoned, but it left a deep mark on organic chemistry:<Annex 1 . Slide 8>
- the concept of "radical" is firmly established in chemistry;
- the statement about the possibility of the existence of free radicals, about the transition in a huge number of reactions of certain groups of atoms from one compound to another, turned out to be true.

In the 40s. 19th century The doctrine of homology was initiated, which made it possible to clarify some relationships between the composition and properties of compounds. Homological series, homological difference were revealed, which made it possible to classify organic substances. The classification of organic substances on the basis of homology led to the emergence of type theory (40-50s of the XIX century, C. Gerard, A. Kekule and others)<Annex 1 . slide 9>

The Essence of Type Theory<Annex 1 . Slide 10>

- The theory is based on an analogy in the reactions between organic and some inorganic substances, taken as types (types: hydrogen, water, ammonia, hydrogen chloride, etc.). Replacing hydrogen atoms in the type of substance with other groups of atoms, scientists predicted various derivatives. For example, the replacement of a hydrogen atom in a water molecule by a methyl radical leads to the formation of an alcohol molecule. Substitution of two hydrogen atoms - to the appearance of an ether molecule<Annex 1 . slide 11>

C. Gerard directly said in this regard that the formula of a substance is only an abbreviated record of its reactions.

All org. substances were considered derivatives of the simplest inorganic substances - hydrogen, hydrogen chloride, water, ammonia<Annex 1 . slide 12>

<Annex 1 . slide 13>

- molecules of organic substances are a system consisting of atoms, the order of connection of which is unknown; the properties of compounds are affected by the totality of all atoms of the molecule;
- it is impossible to know the structure of a substance, since the molecules change during the reaction. The formula of a substance does not reflect the structure, but the reactions in which the given substance. For each substance, one can write as many rational formulas as there are different types of transformations that the substance can experience. The theory of types allowed for a plurality of "rational formulas" for substances, depending on what reactions they want to express with these formulas.

The theory of types played a big role in the development of organic chemistry <Annex 1 . slide 14>

- allowed to predict and discover a number of substances;
- had a positive impact on the development of the doctrine of valency;
- drew attention to the study of chemical transformations of organic compounds, which allowed a deeper study of the properties of substances, as well as the properties of predicted compounds;
- created a systematization of organic compounds that was perfect for that time.

It should not be forgotten that in reality theories arose and succeeded each other not sequentially, but existed simultaneously. Chemists often misunderstood each other. F. Wöhler in 1835 said that “organic chemistry can now drive anyone crazy. It seems to me a dense forest full of wonderful things, a huge thicket without an exit, without an end, where you dare not penetrate ... ".

None of these theories has become a theory of organic chemistry in the full sense of the word. The main reason for the failure of these ideas is their idealistic essence: the internal structure of molecules was considered fundamentally unknowable, and any reasoning about it was quackery.

A new theory was needed, which would stand on materialistic positions. Such a theory was theory of chemical structure A.M. Butlerov <Annex 1 . Slides 15, 16>, which was created in 1861. Everything rational and valuable that was in the theories of radicals and types was subsequently assimilated by the theory of chemical structure.

The need for the appearance of the theory was dictated by:<Annex 1 . Slide 17>

– increased industrial requirements for organic chemistry. It was necessary to provide the textile industry with dyes. In order to develop the food industry, it was necessary to improve the methods of processing agricultural products.
In connection with these problems, new methods for the synthesis of organic substances began to be developed. However, scientists had serious difficulties in the scientific substantiation of these syntheses. So, for example, it was impossible to explain the valency of carbon in compounds using the old theory.
Carbon is known to us as a 4-valent element (This has been proven experimentally). But here it seems to retain this valency only in methane CH 4. In ethane C 2 H 6, according to our ideas, carbon should be. 3-valent, and in propane C 3 H 8 - fractional valency. (And we know that valence must be expressed only in whole numbers).
What is the valency of carbon in organic compounds?

It was not clear why there are substances with the same composition, but different properties: C 6 H 12 O 6 is the molecular formula of glucose, but the same formula is also fructose (a sugary substance - an integral part of honey).

Pre-structural theories could not explain the diversity of organic substances. (Why can carbon and hydrogen, two elements, form such a large number of different compounds?).

It was necessary to systematize the existing knowledge from a unified point of view and develop a unified chemical symbolism.

A scientifically substantiated answer to these questions was given by the theory of the chemical structure of organic compounds, created by the Russian scientist A.M. Butlerov.

Basic prerequisites who paved the way for the emergence of the theory of chemical structure were<Annex 1 . Slide 18>

- the doctrine of valency. In 1853, E. Frankland introduced the concept of valency, established the valence for a number of metals, investigating organometallic compounds. Gradually, the concept of valence was extended to many elements.

An important discovery for organic chemistry was the hypothesis of the ability of carbon atoms to form chains (A. Kekule, A. Cooper).

One of the prerequisites was the development of a correct understanding of atoms and molecules. Until the 2nd half of the 50s. 19th century There were no generally accepted criteria for defining the concepts: "atom", "molecule", "atomic mass", "molecular mass". Only at the International Congress of Chemists in Karlsruhe (1860) were these concepts clearly defined, which predetermined the development of the theory of valence, the emergence of the theory of chemical structure.

The main provisions of the theory of chemical structure of A.M. Butlerov(1861)

A.M. Butlerov formulated the most important ideas of the theory of the structure of organic compounds in the form of basic provisions, which can be divided into 4 groups.<Annex 1 . Slide 19>

1. All atoms that form the molecules of organic substances are connected in a certain sequence according to their valence (i.e., the molecule has a structure).

<Annex 1 . Slides 19, 20>

In accordance with these ideas, the valency of elements is conventionally depicted by dashes, for example, in methane CH 4.<Annex 1 . Slide 20> >

Such a schematic representation of the structure of molecules is called structure formulas and structural formulas. Based on the provisions on the 4-valency of carbon and the ability of its atoms to form chains and cycles, the structural formulas of organic substances can be depicted as follows:<Annex 1 . Slide 20>

In these compounds, carbon is tetravalent. (The dash symbolizes a covalent bond, a pair of electrons).

2. The properties of a substance depend not only on which atoms and how many of them are part of the molecules, but also on the order of connection of atoms in molecules. (i.e. properties depend on the structure) <Annex 1 . Slide 19>

This position of the theory of the structure of organic substances explained, in particular, the phenomenon of isomerism. There are compounds that contain the same number of atoms of the same elements but are bound in a different order. Such compounds have different properties and are called isomers.
The phenomenon of the existence of substances with the same composition, but different structure and properties is called isomerism.<Annex 1 . Slide 21>

The existence of isomers of organic substances explains their diversity. The phenomenon of isomerism was predicted and proved (experimentally) by A.M. Butlerov on the example of butane

So, for example, the composition of C 4 H 10 corresponds to two structural formulas:<Annex 1 . Slide 22>

A different mutual arrangement of carbon atoms in the molecules of UV appears only with butane. The number of isomers increases with the number of carbon atoms of the corresponding hydrocarbon, for example, pentane has three isomers, and decane has seventy-five.

3. By the properties of a given substance, one can determine the structure of its molecule, and by the structure of the molecule, one can predict properties. <Annex 1 . Slide 19>

From the course of inorganic chemistry, it is known that the properties of inorganic substances depend on the structure of crystal lattices. Distinctive properties of atoms from ions are explained by their structure. In the future, we will see that organic substances with the same molecular formulas, but different structures, differ not only in physical, but also in chemical properties.

4. Atoms and groups of atoms in the molecules of substances mutually influence each other.

<Annex 1 . Slide 19>

As we already know, the properties of inorganic compounds containing hydroxo groups depend on whether they are bonded to atoms of metals or nonmetals. For example, both bases and acids contain a hydroxo group:<Annex 1 . Slide 23>

However, the properties of these substances are completely different. The reason for the different chemical nature of the group - OH (in aqueous solution) is due to the influence of atoms and groups of atoms associated with it. With an increase in the non-metallic properties of the central atom, dissociation according to the type of base is weakened and dissociation according to the type of acid increases.

Organic compounds can also have different properties, which depend on which atoms or groups of atoms the hydroxyl groups are attached to.

The question of the mutual infusion of atoms A.M. Butlerov analyzed in detail on April 17, 1879 at a meeting of the Russian Physical and Chemical Society. He said that if two different elements are associated with carbon, for example, Cl and H, then “they here do not depend on each other to the same extent as on carbon: there is no dependence between them, that connection that exists in a particle of hydrochloric acid … But does it follow from this that there is no relationship between hydrogen and chlorine in the CH 2 Cl 2 compound? I answer this with a resounding denial.”

As a specific example, he further cites an increase in the mobility of chlorine during the transformation of the CH 2 Cl group into COCl and says in this regard: “It is obvious that the character of the chlorine in the particle has changed under the influence of oxygen, although this latter did not combine directly with chlorine.”<Annex 1 . Slide 23>

The question of the mutual influence of directly unbound atoms was the main theoretical core of V.V. Morkovnikov.

In the history of mankind, relatively few scientists are known whose discoveries are of worldwide significance. In the field of organic chemistry, such merits belong to A.M. Butlerov. In terms of significance, the theory of A.M. Butlerov is compared with the Periodic Law.

The theory of the chemical structure of A.M. Butlerov:<Annex 1 . Slide 24>

- made it possible to systematize organic substances;
– answered all the questions that had arisen by that time in organic chemistry (see above);
- made it possible to theoretically foresee the existence of unknown substances, to find ways of their synthesis.

Almost 140 years have passed since the TCS of organic compounds was created by A.M. Butlerov, but even now chemists of all countries use it in their work. The latest achievements of science supplement this theory, clarify and find new confirmations of the correctness of its basic ideas.

The theory of chemical structure remains the foundation of organic chemistry today.

TCS of organic compounds A.M. Butlerova made a significant contribution to the creation of a general scientific picture of the world, contributed to the dialectical - materialistic understanding of nature:<Annex 1 . Slide 25>

– the law of transition of quantitative changes into qualitative ones can be traced on the example of alkanes:<Annex 1 . Slide 25>.

Only the number of carbon atoms changes.

– law of unity and struggle of opposites traced to the phenomenon of isomerism<Annex 1 . Slide 26>

Unity - in composition (same), location in space.
The opposite is in the structure and properties (different sequence of arrangement of atoms).
These two substances coexist together.

– law of negation of negation - on isomerism.<Annex 1 . Slide 27>

Isomers coexisting negate each other by their existence.

Having developed the theory, A.M. Butlerov did not consider it absolute and unchangeable. He argued that it should develop. TCS of organic compounds did not remain unchanged. Its further development proceeded mainly in 2 interrelated directions:<Annex 1 . Slide 28>

Stereochemistry is the study of the spatial structure of molecules.

The doctrine of the electronic structure of atoms (allowed to understand the nature of the chemical bond of atoms, the essence of the mutual influence of atoms, to explain the reason for the manifestation of certain chemical properties by a substance).

Chemical structure of a molecule represents its most characteristic and unique side, 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 made to one molecule, small changes in its properties follow (usually affecting physical properties), but if the molecule has experienced deep 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:

1. The presence of certain atoms (C, H, O, N),
2. a certain number of atoms belonging to each class, which are connected 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.

In the presence of a bond between the amino group and another carbon atom (i.e., there has been a slight structural change), which corresponds to beta-alanine:

beta alanine

The general chemical properties are still 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

In the essence of determining the structure of an organic compound, the following principles lie, which follow 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 a constant composition and properties, has 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 method of bonding atoms in organic matter on its properties. He summarized all the knowledge and ideas about the structure of chemical compounds available by that time in the theory of the structure of organic compounds.

The main provisions of the theory of A. M. Butlerov

can be summarized as follows:

1. In the molecule of an organic compound, the atoms are connected in a certain sequence, which determines its structure.
2. The carbon atom in organic compounds has a valence of four.
3. With the same composition of a molecule, several options for connecting the atoms of this molecule to each other are possible. Such compounds having the same composition but different structure were called isomers, and a similar phenomenon was called isomerism.
4. Knowing the structure of an organic compound, one can predict its properties; Knowing the properties of an organic compound, one can predict its structure.
5. 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, the influence of not directly bonded atoms is much weaker.

Pupil A.M. Butlerov - V. V. Markovnikov continued to study the issue of the mutual influence of atoms, which was reflected in 1869 in his dissertation work "Materials on the mutual influence of atoms in chemical compounds."

The merit of A.M. Butlerov and the importance of the theory of chemical structure is exceptionally great for chemical synthesis. The opportunity arose to predict the basic properties of organic compounds, to foresee the ways of their synthesis. Thanks to the theory of chemical structure, chemists first appreciated the molecule as an ordered system with a strict bond order between atoms. And at present, the main provisions of Butlerov's theory, despite changes and clarifications, underlie modern theoretical concepts of organic chemistry.

Categories ,

Lesson content: Theories of the structure of organic compounds: prerequisites for creation, basic provisions. Chemical structure as the order of connection and mutual influence of atoms in molecules. Homology, isomerism. The dependence of the properties of substances on the chemical structure. The 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 the activities of students to familiarize and consolidate the primary provisions 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. Actualization of 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 were the disadvantages of the theory of radicals?

6) What were the shortcomings of type theory?

3. Setting goals and objectives of the lesson.

The concept of valency formed an important part of the theory of the chemical structure of A.M. Butlerov in 1861

The periodic law formulated by D.I. Mendeleev in 1869, revealed the dependence of the valency of an element on its position in the periodic system.

It remained unclear the wide variety of organic substances that have the same qualitative and quantitative composition, but different properties. For example, about 80 different substances were known that corresponded to the composition C 6 H 12 O 2. Jens Jakob Berzelius suggested calling these substances isomers.

Scientists from many countries have paved the way for the creation of a theory explaining the structure and properties of organic substances.

At the congress of German naturalists and doctors in the city of Speyer, a report was read, called "Something in the chemical structure of bodies." The author of the report was Professor of Kazan University 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 up to the present day. This theory made it possible to predict the existence of new compounds and their properties. The concept of the chemical structure made it possible to explain such a mysterious phenomenon as isomerism.

The main provisions of the theory of chemical structure are as follows:
1. Atoms in the molecules of organic substances are connected in a certain sequence according to their valency.

2. The properties of substances are determined by the qualitative, quantitative composition, the order of connection and the mutual influence of atoms and groups of atoms in a molecule.

3. The structure of molecules can be established on the basis of studying their properties.

Let's consider these provisions in more detail. Molecules of organic substances contain carbon atoms (valence IV), hydrogen (valence I), oxygen (valence II), nitrogen (valency III). Each carbon atom in the molecules of organic substances forms four chemical bonds with other atoms, while carbon atoms can be combined into chains and rings. Based on the first position of the theory of chemical structure, we will draw up the structural formulas of organic substances. For example, methane has been found to have the composition CH 4 . Given the valencies 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 look at the manifestation of this regularity on the example of organic substances.

Ethane and ethyl alcohol have different qualitative composition. An alcohol molecule, unlike ethane, contains an oxygen atom. How will this affect 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 methane, ethane, propane and butane hydrocarbons.

Methane, ethane, propane and butane have the same qualitative composition, but different quantitative composition (the number of atoms of each element). According to the second position of the theory of chemical structure, they must 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, an increase in the boiling and melting points occurs, which confirms the dependence of the properties on the quantitative composition of the molecules.

The molecular formula C 4 H 10 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 arrangement 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 of the composition, structure and properties of substances: composition - structure - properties. Consider this using the example of compounds of the composition C 2 H 6 O.

Imagine that we have samples of two substances with the same molecular formula C 2 H 6 O, which was determined in the course of a qualitative and quantitative analysis. But how to find out the chemical structure of these substances? To answer this question will help the study of their physical and chemical properties. When the first substance interacts with metallic sodium, the reaction does not proceed, and the second actively interacts with it with the release of hydrogen. Let us determine the quantitative ratio of substances in the reaction. To do this, we 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 amount of substances. In this case, it turns out that out of two moles of the substance under study, one mole of hydrogen is released. Therefore, each molecule of this substance is a source of one hydrogen atom. What conclusion can be drawn? Only one hydrogen atom differs in properties and, therefore, in structure (with which atoms it is associated) from all the others. Given the valency 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 the study of the properties of substances, one can draw a conclusion about its chemical structure.

The importance of the theory of chemical structure can hardly be overestimated. It provided chemists with a scientific basis for studying the structure and properties of organic substances. The Periodic Law, formulated by D.I. Mendeleev. The theory of structure generalized all the scientific views prevailing in chemistry of 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 certain substances, which were later obtained. Like the Periodic Law, the theory of chemical structure was further developed after the formation of the theory of the structure of the atom, chemical bonding and stereochemistry.