Basic principles of the theory of the chemical structure of organic substances by A. Butlerov

Man has long learned to use various substances to prepare food, dyes, clothing, and medicines. Over time, a sufficient amount of information has accumulated about the properties of certain substances, which has made it possible to improve methods for their production, processing, etc. And it turned out that many mineral (inorganic substances) can be obtained directly.

But some substances used by man were not synthesized by him, because they were obtained from living organisms or plants. These substances were called organic. Organic substances could not be synthesized in the laboratory. At the beginning of the 19th century, such a doctrine as vitalism (vita - life) was actively developing, according to which organic substances arise only thanks to the “vital force” and it is impossible to create them “artificially”.

But as time passed and science developed, new facts appeared about organic substances that ran counter to the existing vitalist theory.

In 1824, the German scientist F. Wöhler synthesized oxalic acid for the first time in the history of chemical science – organic matter from inorganic substances (cyanogen and water):

(CN) 2 + 4H 2 O → COOH - COOH + 2NH 3

In 1828, Wöller heated sodium cyanate with ammonium sulfur and synthesized urea - waste product of animal organisms:

NaOCN + (NH 4) 2 SO 4 → NH 4 OCN → NH 2 OCNH 2

These discoveries played an important role in the development of science in general, and chemistry in particular. Chemical scientists began to gradually move away from vitalistic teaching, and the principle of dividing substances into organic and inorganic revealed its inconsistency.

Currently substances still divided into organic and inorganic, but the separation criterion is slightly different.

Substances are called organic containing carbon, they are also called carbon compounds. There are about 3 million such compounds, the remaining compounds are about 300 thousand.

Substances that do not contain carbon are called inorganic And. But there are exceptions to the general classification: there are a number of compounds that contain carbon, but they belong to inorganic substances (carbon monoxide and dioxide, carbon disulfide, carbonic acid and its salts). All of them are similar in composition and properties to inorganic compounds.

In the course of studying organic substances, new difficulties have arisen: based on theories about inorganic substances, it is impossible to reveal the laws of the structure of organic compounds and explain the valency of carbon. Carbon in different compounds had different valences.

In 1861, the Russian scientist A.M. Butlerov was the first to synthesize a sugary substance.

When studying hydrocarbons, A.M. Butlerov realized that they represent a completely special class of chemicals. Analyzing their structure and properties, the scientist identified several patterns. They formed the basis of the theories of chemical structure.

1. The molecule of any organic substance is not random; the atoms in the molecules are connected to each other in a certain sequence according to their valencies. Carbon in organic compounds is always tetravalent.

2. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structural formula).

3. The chemical structure can be determined using chemical methods. (Modern physical methods are also currently used).

4. The properties of substances depend not only on the composition of the molecules of the substance, but on their chemical structure (the sequence of combination of atoms of elements).

5. By the properties of a given substance one can determine the structure of its molecule, and by the structure of the molecule – anticipate properties.

6. Atoms and groups of atoms in a molecule exert mutual influence on each other.

This theory became the scientific foundation of organic chemistry and accelerated its development. Based on the provisions of the theory, A.M. Butlerov described and explained the phenomenon isomerism, predicted the existence of various isomers and obtained some of them for the first time.

Let's consider the chemical structure of ethane – C2H6. Having designated the valence of elements with dashes, we will depict the ethane molecule in the order of connection of atoms, that is, we will write the structural formula. According to the theory of A.M. Butlerov, it will have the following form:

Hydrogen and carbon atoms are bound into one particle, the valence of hydrogen is equal to one, and that of carbon – four. Two carbon atoms connected by a carbon bond – carbon (C – WITH). Ability of carbon to form C – The C-bond is understandable based on the chemical properties of carbon. The carbon atom has four electrons on its outer electron layer; the ability to give up electrons is the same as the ability to gain missing ones. Therefore, carbon most often forms compounds with a covalent bond, that is, due to the formation of electron pairs with other atoms, including carbon atoms with each other.

This is one of the reasons for the diversity of organic compounds.

Compounds that have the same composition but different structures are called isomers. The phenomenon of isomerism – one of the reasons for the diversity of organic compounds

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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 table of D.I. Mendeleev for 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, such as sugar, vegetable and animal fats, dyes, fragrant and medicinal substances. Gradually, people learned by processing 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 protein substances, nucleic acids, vitamins, etc. Organic chemistry is of great importance for the development of medicine, since the vast majority of medicines are organic compounds not only of natural origin, but also obtained mainly through synthesis. The exceptional significance of the high molecular weight organic compounds (synthetic resins, plastics, fibers, synthetic rubbers, dyes, herbicides, insecticides, fungicides, defoliants...). Organic chemistry is of great importance for the production of food and industrial goods.

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

One of the reasons for the wide variety of organic compounds is the uniqueness of their structure, which is manifested in the formation of covalent bonds and chains by carbon atoms, varying in type and length. Moreover, 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 chains may contain oxygen, nitrogen, sulfur, phosphorus, arsenic, silicon, tin, lead, titanium, iron, etc.

The manifestation of these properties by carbon is due to several reasons. It was confirmed that the energies of the C–C and C–O bonds are comparable. Carbon has the ability to form three types of orbital hybridization: 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 ─). Moreover, carbon atoms form these types of bonds 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 their properties.

It also fully confirms the basics 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 valence, 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 the 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, unclosed carbon chain - straight or branched:

N N N N N N N

│ │ │ │ │ │ │

N─ S─S─S─S─ N H─S─S─S─N

│ │ │ │ │ │ │

N N N N N │ N

Normal butane isobutane (methylpropane)

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

cyclobutane cyclohexane

b) Aromatic compounds, the molecules of which contain a benzene skeleton - a six-membered ring 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 distributed 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 are distinguished:

1. Extremely saturated– the carbon skeleton contains only single bonds.

─С─С─С─

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

─С=С─ ─С≡С─

3. Aromatic– unsaturated cycles with ring conjugation (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 O

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 theories of the chemical structure of organic compounds.

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

A.M. Butlerov denied this opinion. He came from the right place 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 experimentally by studying the chemical transformations of a substance. Conversely, knowing the structure of the molecule, one can deduce 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 laws. The basic principles of his theory A.M. Butlerov outlined it in his report “On the theory of chemical structure.”

The main principles 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 valence. The order in which the atoms bond is called chemical structure;

2) the properties of a substance depend not only on which atoms and in what quantity are included in its molecule, but also on the order in which they are connected to each other, i.e., on the chemical structure of the molecule;

3) atoms or groups of atoms that form 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 depict the order in which atoms are combined in molecules are called structural formulas or formulas of structure.

The importance of the theory of chemical structure of A.M. Butlerova:

1) is the most important part of the theoretical foundation of organic chemistry;

2) in importance it can be compared with the Periodic Table of Elements by 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 for all research in organic chemistry.

12 Phenols, hydroxy derivatives aromatic compounds, containing one or more hydroxyl groups (–OH) bonded to the carbon atoms of the aromatic nucleus. Based on the number of OH groups, monoatomic compounds are distinguished, for example, oxybenzene C 6 H 5 OH, usually called simply phenol, hydroxytoluenes 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; highly soluble in organic solvents (alcohol, ether, oensol). Possessing acidic properties, phosphorus forms salt-like products - phenolates: ArOH + NaOH (ArONa + H 2 O (Ar is an aromatic radical). Alkylation and acylation of phenolates leads to phosphorus esters - simple ArOR and complex ArOCOR (R is an organic radical). Esters can be obtained by direct reaction 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 of F. is replaced with halogen with great difficulty. Electrophilic substitution in the phosphorus nucleus (halogenation, nitration, sulfonation, alkylation, etc.) is carried out much more easily than in unsubstituted aromatic hydrocarbons; replacement groups are sent to ortho- And pair-position to the OH group (see. Orientation rules). 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 are used in industry to produce phenol and resorcinol-formaldehyde resins, diphenylolpropane, and other important products.

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

13 Alkanes

general characteristics

Hydrocarbons are the simplest organic compounds consisting of two elements: carbon and hydrogen. Saturated 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 the molecules of saturated hydrocarbons, carbon atoms are connected to each other 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 "low affinity").

The first member of the homologous series of alkanes is methane CH4. 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 with the fifth hydrocarbon, the name is formed from the Greek numeral, indicating the number of carbon atoms in the molecule, and the ending -an. This is pentane C 5 H 12 hexane C 6 H 14, heptane C 7 H 16, octane C 8 H 18, nonane C 9 H 20, decane C 10 H 22, etc.

In the homologous series, a gradual change in the physical properties of hydrocarbons is observed: boiling and melting points increase, density increases. Under normal conditions (temperature ~ 22°C), the first four members of the series (methane, ethane, propane, butane) are gases, from C 5 H 12 to C 16 H 34 are liquids, and from 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 a straight 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 removed from an alkane molecule, single-valent 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 relevant examples:

Radicals are formed not only by organic, but also by inorganic compounds. So, if you subtract the hydroxyl group OH from nitric acid, you 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 -ane replaced by -ylidene (if the hydrogen atoms are separated from one carbon atom) or -ylene (if the hydrogen atoms are removed from two adjacent carbon atoms). The radical CH 2 = is called methylene.

The names of radicals are used in the nomenclature of many hydrocarbon derivatives. 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).

To name isomers, two nomenclatures are widely used: old - rational and modern - substitutive, 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 to be derivatives of methane, in which one or more hydrogen atoms are replaced by radicals. If the same radicals are repeated several times in a 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 substitutive 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 selected and the atoms of the chain are numbered from the end to which the hydrocarbon radical is closest. Then they call: 1) the number of the carbon atom to which the radical is associated (starting with the simplest radical); 2) a hydrocarbon that has a long chain. If the formula contains several identical radicals, then before their names 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 called according to this nomenclature:

Here's a more complex example:

Both substitutive 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 different positions in them. A carbon atom that is bonded to only one carbon atom in the chain is called primary, to two is called secondary, to three is tertiary, and to four is 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 whether they are bonded to a primary, secondary, or tertiary carbon atom. This should 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. As the relative molecular weight increases, the boiling and melting points of alkanes increase. With the same number of carbon atoms in the 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 are easily mixed 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.

Among the synthetic methods for producing alkanes, the following can be distinguished:

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

CH 3 -C≡CH + 2H 2 → CH 3 -CH 2 -CH 3.

2. Preparation from halogenated conductors. When monohalogenated alkanes are heated with sodium metal, alkanes with double 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.

This reaction is not carried out with two different halogenated alkanes because it results in a mixture of three different alkanes

3. Preparation 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 = 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. Non-polar C-C and C-H bonds in alkanes are not prone to ionic cleavage, but are capable of homolytic cleavage under the influence of active free radicals. Therefore, alkanes are characterized by radical reactions, which result in compounds where hydrogen atoms are replaced by other atoms or groups of atoms. Consequently, alkanes enter into reactions that proceed through a radical substitution mechanism, 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 react with halogens (chlorine and bromine) under the influence 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) Growth of the chain. The chlorine radical removes a hydrogen atom from the alkane molecule:

Cl + CH 4 →HCl + CH 3

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

CH 3 + Cl 2 →CH 3 Cl + Cl

These reactions are repeated until the chain breaks in one of the 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), hydrogen atoms at the tertiary carbon atoms are mixed first, then at the secondary and primary carbon atoms. This is explained by the fact that the bond between the tertiary carbon atom and 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, under certain conditions, transform into branched-chain alkanes:

4. Cracking is the hemolytic cleavage of C-C bonds, which occurs when heated and under the influence 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 + ZN 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. By mild oxidation of methane with atmospheric oxygen in the presence of various catalysts, methyl alcohol, formaldehyde, and formic acid can be obtained:

Mild 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 + (3n+1)/2O 2 = 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. The carbon atoms at the double bond are in the 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 “-ane” with “-ene”; 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.

Physical properties

Melting and boiling points increase with molecular weight and length of the carbon backbone.
Under normal conditions, alkenes from C2H4 to C4H8 are gases; from C5H10 to C17H34 - liquids, after C18H36 - solids. Alkenes are insoluble in water, but are highly 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 at 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 harsh conditions - the alkene is oxidized to acid:

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

Double connection connection:
CH2=CH2 +Br2 → CH2Br-CH2Br

Oxidation with peracids:
CH2=CH2 + CH3COOOH →
or
CH2=CH2 + HCOOH → HOCH2CH2OH

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 valency 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 valence.

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 (valency 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.

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.

Chemical 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:

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 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:

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 basic idea of ​​the theory of chemical structure, which consists in the influence of the way 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:

1. In a 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 valency of four.
3. 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.
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, 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.