The first appeared at the beginning of the 19th century. radical theory(J. Gay-Lussac, F. Wehler, J. Liebig). Radicals are groups of atoms that pass without change during chemical reactions from one compound to another. This concept of radicals has been preserved, but most other provisions of the theory of radicals turned out to be incorrect.
According to type theories(C. Gerard) all organic substances can be divided into types corresponding to certain inorganic substances. For example, alcohols R-OH and ethers R-O-R were considered to be representatives of the water type H-OH, in which the hydrogen atoms are replaced by radicals. The theory of types created a classification of organic substances, some of the principles of which are used today.
The modern theory of the structure of organic compounds was created by the outstanding Russian scientist A.M. Butlerov.
Basic principles of the theory of the structure of organic compounds by A.M. Butlerov
1. Atoms in a molecule are arranged in a certain sequence according to their valency. The valency of the carbon atom in organic compounds is four.
2. The properties of substances depend not only on which atoms and in what quantities are included in the molecule, but also on the order in which they are connected to each other.
3. Atoms or groups of atoms that make up a molecule mutually influence each other, which determines the chemical activity and reactivity of the molecules.
4. Studying the properties of substances allows us to determine their chemical structure.
The mutual influence of neighboring atoms in molecules is the most important property of organic compounds. This influence is transmitted either through a chain of simple bonds or through a chain of conjugated (alternating) simple and double bonds.
Classification of organic compounds is based on the analysis of two aspects of the structure of molecules - the structure of the carbon skeleton and the presence of functional groups.
Organic compounds
Hydrocarbons Heterocyclic compounds
Limit- Unprecedent- Aroma-
efficient practical
Aliphatic Carbocyclic
Ultimate Unsaturated Ultimate Unsaturated Aromatic
(Alkanes) (Cycloalkanes) (Arenas)
WITH P H 2 P+2 C P H 2 P WITH P H 2 P -6
alkenes, polyenes and alkynes
WITH P H 2 P polyines C P H 2 P -2
Rice. 1. Classification of organic compounds according to the structure of the carbon skeleton
Classes of hydrocarbon derivatives based on the presence of functional groups:
Halogen derivatives R–Gal: CH 3 CH 2 Cl (chloroethane), C 6 H 5 Br (bromobenzene);
Alcohols and phenols R–OH: CH 3 CH 2 OH (ethanol), C 6 H 5 OH (phenol);
Thiols R–SH: CH 3 CH 2 SH (ethanethiol), C 6 H 5 SH (thiophenol);
Ethers R–O–R: CH 3 CH 2 –O–CH 2 CH 3 (diethyl ether),
complex R–CO–O–R: CH 3 CH 2 COOCH 2 CH 3 (ethyl acetic acid);
Carbonyl compounds: aldehydes R–CHO:
ketones R–СО–R: CH 3 COCH 3 (propanone), C 6 H 5 COCH 3 (methyl phenylketone);
Carboxylic acids R-COOH: (acetic acid), (benzoic acid)
Sulfonic acids R–SO 3 H: CH 3 SO 3 H (methanesulfonic acid), C 6 H 5 SO 3 H (benzenesulfonic acid)
Amines R–NH 2: CH 3 CH 2 NH 2 (ethylamine), CH 3 NHCH 3 (dimethylamine), C 6 H 5 NH 2 (aniline);
Nitro compounds R–NO 2 CH 3 CH 2 NO 2 (nitroethane), C 6 H 5 NO 2 (nitrobenzene);
Organometallic (organoelement) compounds: CH 3 CH 2 Na (ethyl sodium).
A series of compounds similar in structure, possessing similar chemical properties, in which individual members of the series differ from each other only in the number of -CH 2 - groups, is called homologous series, and the -CH 2 group is a homological difference . For members of a homologous series, the vast majority of reactions proceed in the same way (with the exception of only the first members of the series). Consequently, knowing the chemical reactions of only one member of the series, it can be stated with a high degree of probability that the same type of transformation occurs with the remaining members of the homologous series.
For any homologous series, a general formula can be derived that reflects the relationship between the carbon and hydrogen atoms of the members of this series; like this the formula is called general formula of the homologous series. Yes, S P H 2 P+2 – formula of alkanes, C P H 2 P+1 OH – aliphatic monohydric alcohols.
Nomenclature of organic compounds: trivial, rational and systematic nomenclature. Trivial nomenclature is a collection of historically established names. So, from the name it is immediately clear where malic, succinic or citric acid was isolated, how pyruvic acid was obtained (pyrolysis of grape acid), connoisseurs of the Greek language will easily guess that acetic acid is something sour, and glycerin is sweet. As new organic compounds were synthesized and the theory of their structure developed, other nomenclatures were created that reflected the structure of the compound (its belonging to a certain class).
Rational nomenclature constructs the name of a compound based on the structure of a simpler compound (the first member of a homologous series). CH 3 HE– carbinol, CH 3 CH 2 HE– methylcarbinol, CH 3 CH(OH) CH 3 – dimethylcarbinol, etc.
IUPAC nomenclature (systematic nomenclature). According to IUPAC (International Union of Pure and Applied Chemistry) nomenclature, the names of hydrocarbons and their functional derivatives are based on the name of the corresponding hydrocarbon with the addition of prefixes and suffixes inherent in this homologous series.
To correctly (and unambiguously) name an organic compound using systematic nomenclature, you must:
1) select the longest sequence of carbon atoms (parental structure) as the main carbon skeleton and give its name, paying attention to the degree of unsaturation of the compound;
2) identify All functional groups present in the compound;
3) establish which group is senior (see table), the name of this group is reflected in the name of the compound in the form of a suffix and it is placed at the end of the name of the compound; all other groups are given in the name in the form of prefixes;
4) number the carbon atoms of the main chain, giving the highest group the lowest number;
5) list the prefixes in alphabetical order (in this case, multiplying prefixes di-, tri-, tetra-, etc. are not taken into account);
6) write down the full name of the compound.
|
Connection class |
Functional group formula |
Suffix or ending |
|
|
Carboxylic acids |
Carboxy- |
Oic acid |
|
|
Sulfonic acids |
Sulfonic acid |
||
|
Aldehydes | |||
|
Hydroxy- | |||
|
Mercapto- | |||
|
С≡≡С | |||
|
Halogen derivatives |
Br, I, F, Cl |
Bromine-, iodine-, fluorine-, chlorine- |
-bromide, -iodide, -fluoride, -chloride |
|
Nitro compounds |
It is necessary to remember:
In the names of alcohols, aldehydes, ketones, carboxylic acids, amides, nitriles, acid halides, the suffix defining the class follows the suffix of the degree of unsaturation: for example, 2-butenal;
Compounds containing other functional groups are called hydrocarbon derivatives. The names of these functional groups are placed as prefixes before the name of the parent hydrocarbon: for example, 1-chloropropane.
The names of acidic functional groups, such as sulfonic acid or phosphinic acid, are placed after the name of the hydrocarbon skeleton: for example, benzenesulfonic acid.
Derivatives of aldehydes and ketones are often named after the parent carbonyl compound.
Esters of carboxylic acids are called derivatives of parent acids. The ending –oic acid is replaced by –oate: for example, methyl propionate is the methyl ester of propanoic acid.
To indicate that the substituent is bonded to the nitrogen atom of the parent structure, use a capital letter N before the name of the substituent: N-methylaniline.
Those. you need to start with the name of the parent structure, for which it is absolutely necessary to know by heart the names of the first 10 members of the homologous series of alkanes (methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane). You also need to know the names of the radicals formed from them - in this case, the ending -an changes to -il.
Consider a compound that is part of drugs used to treat eye diseases:
CH 3 – C(CH 3) = CH – CH 2 – CH 2 – C(CH 3) = CH – CHO
The basic parent structure is a chain of 8 carbon atoms, including an aldehyde group and both double bonds. Eight carbon atoms are octane. But there are 2 double bonds - between the second and third atoms and between the sixth and seventh. One double bond - the ending -an must be replaced with -ene, there are 2 double bonds, which means -diene, i.e. octadiene, and at the beginning we indicate their position, naming the atoms with lower numbers - 2,6-octadiene. We have dealt with the original structure and indefiniteness.
But the compound contains an aldehyde group, it is not a hydrocarbon, but an aldehyde, so we add the suffix -al, without a number, it is always the first - 2,6-octadienal.
Another 2 substituents are methyl radicals at the 3rd and 7th atoms. So, in the end we get: 3,7-dimethyl - 2,6-octadienal.
Basic principles of the theory of chemical structure of A.M. Butlerov
1. Atoms in molecules are connected to each other in a certain sequence according to their valencies. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structure formula).
2. The chemical structure can be determined using chemical methods. (Modern physical methods are also currently used).
3. The properties of substances depend on their chemical structure.
4. Based on the properties of a given substance, one can determine the structure of its molecule, and based on the structure of the molecule, one can predict the properties.
5. Atoms and groups of atoms in a molecule have a mutual influence on each other.
Butlerov's theory was the scientific foundation of organic chemistry and contributed to its rapid development. Based on the provisions of the theory, A.M. Butlerov explained the phenomenon of isomerism, predicted the existence of various isomers and obtained some of them for the first time.
The development of the theory of structure was facilitated by the work of Kekule, Kolbe, Cooper and Van't Hoff. However, their theoretical positions were not of a general nature and served mainly to explain experimental material.
2. Structure formulas
The structure formula (structural formula) describes the order of connection of atoms in a molecule, i.e. its chemical structure. Chemical bonds in the structural formula are represented by dashes. The bond between hydrogen and other atoms is usually not indicated (such formulas are called abbreviated structural formulas).
For example, the full (expanded) and abbreviated structural formulas of n-butane C4H10 have the form:
Another example is isobutane formulas.
Often an even shorter notation of the formula is used, when not only the bonds with the hydrogen atom, but also the symbols of the carbon and hydrogen atoms are not depicted. For example, the structure of benzene C6H6 is reflected by the formulas:
Structural formulas differ from molecular (gross) formulas, which show only which elements and in what proportion are included in the composition of the substance (i.e., qualitative and quantitative elemental composition), but do not reflect the order of bonding of atoms.
For example, n-butane and isobutane have the same molecular formula C4H10, but a different sequence of bonds.
Thus, the difference in substances is due not only to different qualitative and quantitative elemental compositions, but also to different chemical structures, which can only be reflected by structural formulas.
3. The concept of isomerism
Even before the creation of the theory of structure, substances with the same elemental composition, but with different properties, were known. Such substances were called isomers, and this phenomenon itself was called isomerism.
The basis of isomerism, as shown by A.M. Butlerov, lies the difference in the structure of molecules consisting of the same set of atoms. Thus,
isomerism is the phenomenon of the existence of compounds that have the same qualitative and quantitative composition, but different structures and, therefore, different properties.
For example, when a molecule contains 4 carbon atoms and 10 hydrogen atoms, the existence of 2 isomeric compounds is possible:
Depending on the nature of the differences in the structure of isomers, structural and spatial isomerism are distinguished.
4. Structural isomers
Structural isomers are compounds of the same qualitative and quantitative composition, differing in the order of bonding of atoms, i.e. chemical structure.
For example, the composition C5H12 corresponds to 3 structural isomers:
Another example:
5. Stereoisomers
Spatial isomers (stereoisomers), with the same composition and the same chemical structure, differ in the spatial arrangement of atoms in the molecule.
Spatial isomers are optical and cis-trans isomers (different colored balls represent different atoms or atomic groups):
The molecules of such isomers are spatially incompatible.
Stereoisomerism plays an important role in organic chemistry. These issues will be considered in more detail when studying compounds of individual classes.
6. Electronic representations in organic chemistry
The application of the electronic theory of atomic structure and chemical bonding in organic chemistry was one of the most important stages in the development of the theory of the structure of organic compounds. The concept of chemical structure as a sequence of bonds between atoms (A.M. Butlerov) was supplemented by electronic theory with concepts of electronic and spatial structure and their influence on the properties of organic compounds. It is these ideas that make it possible to understand the ways of transmitting the mutual influence of atoms in molecules (electronic and spatial effects) and the behavior of molecules in chemical reactions.
According to modern concepts, the properties of organic compounds are determined by:
the nature and electronic structure of atoms;
the type of atomic orbitals and the nature of their interaction;
type of chemical bonds;
chemical, electronic and spatial structure of molecules.
7. Properties of the electron
The electron has a dual nature. In different experiments it can exhibit the properties of both a particle and a wave. The movement of an electron obeys the laws of quantum mechanics. The connection between the wave and corpuscular properties of the electron reflects the de Broglie relation.
The energy and coordinates of an electron, like other elementary particles, cannot be simultaneously measured with the same accuracy (Heisenberg's uncertainty principle). Therefore, the movement of an electron in an atom or molecule cannot be described using a trajectory. An electron can be located at any point in space, but with different probabilities.
The part of space in which there is a high probability of finding an electron is called an orbital or electron cloud.
For example:
8. Atomic orbitals
Atomic orbital (AO) is the region where an electron is most likely to reside (electron cloud) in the electric field of the atomic nucleus.
The position of an element in the Periodic Table determines the type of orbitals of its atoms (s-, p-, d-, f-AO, etc.), differing in energy, shape, size and spatial orientation.
Elements of the 1st period (H, He) are characterized by one AO - 1s.
In elements of the 2nd period, electrons occupy five AOs at two energy levels: the first level 1s; second level - 2s, 2px, 2py, 2pz. (numbers indicate the energy level number, letters indicate the shape of the orbital).
The state of an electron in an atom is completely described by quantum numbers.
Created by A.M. Butlerov in the 60s of the 19th century, the theory of the chemical structure of organic compounds brought the necessary clarity to the reasons for the diversity of organic compounds, revealed the relationship between the structure and properties of these substances, made it possible to explain the properties of already known and predict the properties of yet undiscovered organic compounds.
Discoveries in the field of organic chemistry (tetravalency of carbon, the ability to form long chains) allowed Butlerov in 1861 to formulate the main generations of the theory:
1) Atoms in molecules are connected according to their valence (carbon-IV, oxygen-II, hydrogen-I), the sequence of atom connections is reflected by structural formulas.
2) The properties of substances depend not only on the chemical composition, but also on the order of connection of atoms in the molecule (chemical structure). Exist isomers, that is, substances that have the same quantitative and qualitative composition, but different structures, and, therefore, different properties.
C 2 H 6 O: CH 3 CH 2 OH - ethyl alcohol and CH 3 OCH 3 - dimethyl ether
C 3 H 6 – propene and cyclopropane - CH 2 =CH−CH 3
3) Atoms mutually influence each other, this is a consequence of the different electronegativity of the atoms forming the molecules (O>N>C>H), and these elements have different effects on the displacement of common electron pairs.
4) Based on the structure of a molecule of an organic substance, one can predict its properties, and based on its properties, one can determine its structure.
TSOS received further development after the establishment of the structure of the atom, the adoption of the concept of types of chemical bonds, types of hybridization, and the discovery of the phenomenon of spatial isomerism (stereochemistry).
Ticket No. 7 (2)
Electrolysis as a redox process. Electrolysis of melts and solutions using sodium chloride as an example. Practical application of electrolysis.
Electrolysis is a redox process that occurs on the electrodes when a direct electric current passes through a melt or electrolyte solution
The essence of electrolysis is the implementation of chemical reactions using electrical energy. The reactions are reduction at the cathode and oxidation at the anode.
The cathode(-) gives electrons to the cations, and the anode(+) accepts electrons from the anions.
NaCl melt electrolysis
NaCl-―>Na + +Cl -
K(-): Na + +1e-―>Na 0 | 2 percent recovery
A(+) :2Cl-2e-―>Cl 2 0 | 1 percent oxidation
2Na + +2Cl - -―>2Na+Cl 2
Electrolysis of aqueous NaCl solution
In the electrolysis of NaC| Na + and Cl - ions, as well as water molecules, participate in water. When current passes, Na + cations move towards the cathode, and Cl - anions move towards the anode. But at the cathode Instead of Na ions, water molecules are reduced:
2H 2 O + 2e-―> H 2 +2OH -
and chloride ions are oxidized at the anode:
2Cl - -2e-―>Cl 2
As a result, there is hydrogen at the cathode, chlorine at the anode, and NaOH accumulates in the solution
In ionic form: 2H 2 O+2e-―>H 2 +2OH-
2Cl - -2e-―>Cl 2
electrolysis
2H 2 O+2Cl - -―>H 2 +Cl 2 +2OH -
electrolysis
In molecular form: 2H 2 O+2NaCl-―> 2NaOH+H 2 +Cl 2
Application of electrolysis:
1)Protection of metals from corrosion
2) Obtaining active metals (sodium, potassium, alkaline earth, etc.)
3) Purification of certain metals from impurities (electric refining)
Ticket No. 8 (1)
Related information:
- A) Theory of knowledge is a science that studies the forms, methods and techniques of the emergence and patterns of development of knowledge, its relationship to reality, the criteria of its truth.
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 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 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 according to the 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 tertiary carbon atoms are mixed first, then at 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:
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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.
| 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 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