Drawing up chemical formulas. Drawing up a structural formula by name
Instructions
To determine the valence of atoms when drawing up structural formulas, use periodic system... A three-dimensional structural formula will help to show the exact distance of atoms in a molecule.
Sources:
- structural formula of substances
- Formulation of complex compounds
Some people still recall with a shudder the school chemistry lessons in which it was necessary to draw up structural formulas hydrocarbons and their isomers. Meanwhile, there is nothing super complicated in this. It is enough to be guided by a certain algorithm when drawing up formulas.
Instructions
Check out the molecular formula for a hydrocarbon. Based on it, make up the formula first of the unbranched carbon skeleton (carbon chain).
Reduce the carbon chain by one atom. Arrange it as a side branch of the carbon chain. Do not forget that the atoms that are located at the outermost atoms of the chain are side branches.
Determine which edge the side branch is closer to. Re-number the carbon chain starting at this end. Arrange the hydrogen atoms according to the carbon.
Determine if the side branch can be located at other carbon atoms in the chain. In case of positive conclusions, compose formulas... If this is not possible, reduce the main carbon chain by another atom and arrange it as another side branch. Please note: no more than 2 side branches can be placed near one carbon.
Arrange the serial numbers above from the edge to which the side branch is closest. Place hydrogen atoms near each atom, taking into account the valence of carbon.
Check again to see if there is a possibility of side branching on other carbons in the main chain. If possible, then compose formulas possible isomers, if not, reduce the carbon chain by another atom and arrange it as a side branch. Now number the whole chain of atoms and try again to make formulas isomers. In the event that two side branches are already at the same distance from the edges of the chain, start numbering from the edge with more side branches.
Continue these steps until you have exhausted all the possibilities for the location of the side branches.
For the convenience of recording the chemical composition and structure chemical certain compilation rules were created chemical formulas using special symbols, numbers and auxiliary characters.
Instructions
Chemical formulas in writing chemical equations, schematic representation chemical processes, connections. For them, the so-called language is used, which is a set legend, such as symbols of chemical elements, the number of atoms of each element in the described substance, etc.
Symbols of chemical elements - one or more letters of the Latin alphabet, of which the first is capital. This is a schematic record of the full name of the element, for example, Ca is calcium or lat. Calcium.
The number of atoms is expressed in mathematical numbers, for example, H_2 is two hydrogen atoms.
There are several ways to record chemical formulas: simplest, empirical, rational and. The simplest record reflects the ratio of chemical elements indicating atomic mass, which is indicated after the sign of the chemical element in the form of a subscript. For example, H_2O is the simplest formula for a water molecule, i.e. two hydrogen atoms and one oxygen atom.
Empirical is different from the simplest topics, which reflects the composition of the substance, but not the structure of the molecules. The formula shows the number of atoms in one molecule, which is also shown as a subscript.
The difference between the simplest and the empirical formulas is shown by the entry formulas benzene: CH and C_6H_6, respectively. Those. The simplest formula shows the direct ratio of carbon and hydrogen atoms, while the empirical one says that a substance molecule contains 6 carbon atoms and 6 hydrogen atoms.
A rational formula clearly shows the presence of atoms of elements in a compound. Such groups are in parentheses, and their number is indicated by a subscript after the parentheses. The formula also uses square brackets, which enclose complex compounds of atoms (compounds with a neutral molecule, ion).
The structural formula is depicted graphically in two or three dimensions. Chemical bonds between the atoms are depicted as lines, while the atoms are indicated as many times as they are involved in the connection. Most clearly, the formula of a substance is expressed by a three-dimensional image, which show the relative position of atoms and the distance between them.
Related Videos
Hydrocarbon is organic matter, which contains only two elements: carbon and hydrogen. It can be limiting, unsaturated with a double or triple bond, cyclic and aromatic.
Compilation of the names of organic compounds according to the structural formula.
Let's do the reverse task. Let's compose the name of the organic compound according to its structural formula. (Read the rules for composing the names of organic compounds. Write the name of an organic compound according to the structural formula.)
4. Variety of organic compounds.
Every day the amount of organic substances extracted and described by chemists increases by almost a thousand. Now about 20 million of them are known ( inorganic compounds exists ten times less).
The reason for the variety of organic compounds is the uniqueness of carbon atoms, namely:
- a sufficiently high valency - 4;
Possibility to create simple, double and triple covalent bonds;
The ability to combine with each other;
The possibility of the formation of linear chains, branched, as well as closed, which are called cycles.
Among organic substances, the largest are the compounds of Carbon with Hydrogen; they are called hydrocarbons. This name comes from the old names for the elements - "carbon" and "hydrogen".
The modern classification of organic compounds is based on the theory chemical structure... The classification is based on the structural features of the carbon chain of hydrocarbons, since they are simple in composition and in most of the known organic substances, hydrocarbon radicals constitute the main part of the molecule.
5. Classification of saturated hydrocarbons.
Organic compounds can be classified:
1) according to the structure of their carbon frame. This classification is based on four main classes of organic compounds (aliphatic compounds, alicyclic compounds, aromatic compounds and heterocyclic compounds);
2) by functional groups.
Acyclic ( non-cyclic, chain) compounds are also called fatty or aliphatic. These names are due to the fact that one of the first well-studied compounds of this type were natural fats.
Among the variety of organic compounds, groups of substances can be distinguished that are similar in their properties and differ from each other by a group - CH 2.
Ø Compounds that are similar in chemical properties and whose composition differs from each other by a group - CH 2, are called homologues.
Ø Homologues, arranged in ascending order of their relative molecular weight, form homologous series.
Ø Group - CH2 2, called homologous difference.
An example of a homologous series can be a number of saturated hydrocarbons (alkanes). Its simplest representative is CH 4 methane. The ending - an typical for the names of saturated hydrocarbons. Next are ethane C 2 H 6, propane CZH 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... These are pentane C 5 H 12, hexane C 6 H 14, heptane C 7 H 16, octane C 8 H 18, nonane CdH 20, decane C 10 H 22, etc.
The formula for any next homologue can be obtained by adding the previous hydrocarbon of the homologous difference to the formula.
Four C-H connections, for example, in methane, are equivalent and placed symmetrically (tetrahedrally) at an angle of 109 0 28 relative to each other. This is because one 2s and three 2p orbitals combine to form four new (identical) orbitals that can provide stronger bonds. These orbitals are directed towards the vertices of the tetrahedron - such an arrangement when the orbitals are as far away from each other as possible. These new orbitals are called sp 3
- hybridized atomic orbitals.
The most convenient nomenclature, which makes it possible to name any compounds, issystematici nomenclature of organic compounds.
Most often, systematic names are based on the principle of substitution, that is, any compound is considered as an unbranched hydrocarbon - acyclic or cyclic, in the molecule of which one or more hydrogen atoms are replaced by other atoms and groups, including hydrocarbon residues. With development organic chemistry the systematic nomenclature is constantly being improved and supplemented, followed by the Nomenclature Commission of the International Union of Pure and Applied Chemistry (IUPAC).
Alkane nomenclature and their derivatives names the first ten members of the saturated hydrocarbon series have already been given. To emphasize that the alkane had an unbranched carbon chain, the word normal (n-) is often added to the name, for example:
When a hydrogen atom is removed from an alkane molecule, monovalent particles are formed, which are called hydrocarbon radicals(abbreviated as R.
The names of monovalent radicals come from the names of the corresponding hydrocarbons with the ending substitution - an on -il (-il). Here are relevant examples:
Knowledge control:
1. What does organic chemistry study?
2. How to distinguish organic from inorganic substances?
3. Is the element of duty included in organic compounds?
4. Reheal types organic reactions.
5. Record the butane isomers.
6. What compounds are called saturated?
7. Which nomenclatures do you know? What is their essence?
8. What are isomers? Give examples.
9. What is a structural formula?
10. Write down the sixth representative of alkanes.
11. How are organic compounds classified?
12. What methods of breaking the connection do you know?
13. Reheal types of organic reactions.
HOMEWORK
Work through: P1. Pages 4-6 L1. Pages 8-12, retelling of the lecture notes №8.
Lecture number 9.
Topic: Alkanes: homologous series, isomerism and nomenclature of alkanes. Chemical properties of alkanes (for example, methane and ethane): combustion, substitution, decomposition and dehydrogenation. Application of alkanes based on properties.
alkanes, homologous series of alkanes, cracking, homologues, homologous difference, structure of alkanes: type of hybridization - sp 3.
Study plan of the topic
1. Saturated hydrocarbons: composition, structure, nomenclature.
2. Types of chemical reactions characteristic of organic compounds.
3.Physical properties(using methane as an example).
4. Getting saturated hydrocarbons.
5. Chemical properties.
6. Application of alkanes.
1. Saturated hydrocarbons: composition, structure, nomenclature.
Hydrocarbons- the simplest organic compounds, consisting of two elements: carbon and hydrogen.
Alkanes or saturated hydrocarbons (international name), refers to hydrocarbons in the molecules of which the carbon atoms are connected to each other by simple (single) bonds, and the valencies of carbon atoms that do not take part in their mutual combination form bonds with hydrogen atoms.
Alkanes form a homologous series of compounds corresponding to the general formula C n H 2n + 2,
where: NS
- the number of carbon atoms.
In the molecules of saturated hydrocarbons, carbon atoms are linked to each other by a simple (single) bond, and the rest of the valencies are saturated with hydrogen atoms. Alkanes are also called paraffins.
For the name of saturated hydrocarbons, they are mainly used systematic and rational nomenclature.
Systematic nomenclature rules.
The general (generic) name for saturated hydrocarbons is alkanes. The names of the first four members of the methane homologous series are trivial: methane, ethane, propane, butane. Starting from the fifth name, they are formed from the Greek numerals with the addition of the suffix -an (this emphasizes the similarity of all saturated hydrocarbons with the ancestor of this series - methane). For the simplest hydrocarbons of the iso-structure, their non-systematic names are retained: isobutane, isopentane, neopentad.
By rational nomenclature alkanes are considered as derivatives of the simplest hydrocarbon - methane, in the molecule of which one or more hydrogen atoms are replaced by radicals. These substituents (radicals) are named in order of precedence (from less complex to more complex). If these substituents are the same, then indicate their number. The name is based on the word "methane":
They have their own nomenclature and radicals(hydrocarbon radicals). Monovalent radicals are called alkyls
and denoted by the letter R or Alk.
Their general formula
C n H 2n + 1.
The names of the radicals are formed from the names of the corresponding hydrocarbons by replacing the suffix -an on the suffix -il(methane - methyl, ethane - ethyl, propane - propyl, etc.).
Divalent radicals are named, replacing the suffix -an on -ilidene (exception - methylene radical == CH 2).
Trivalent radicals have the suffix -ylidine (exception - radical methine == CH).
The table shows the names of the first five hydrocarbons, their radicals, possible isomers and the corresponding formulas.
|
2.Types of chemical reactions typical for organic compounds
1) Oxidation (combustion) reactions:
Such reactions are typical for all representatives of homologous series 2) Substitution reactions:
Such reactions are typical for alkanes, arenes (under certain conditions), and also possible for representatives of other homologous series.
3) Cleavage reactions: Such reactions are possible for alkanes, alkenes.
4) Attachment reactions:
Such reactions are possible for alkenes, alkynes, arenes.
The simplest organic matter - methane- has the molecular formula CH 4. Methane structural formula:
Electronic formula of methane:
Methane molecule has the shape of a tetrahedron: in the center - a carbon atom, in the vertices - hydrogen atoms, the connections are directed to the vertices of the tetrahedron at an angle.
3. Physical properties of methane . The gas is colorless and odorless, lighter than air, slightly soluble in water. In nature, methane is formed during decay. plant residues without air access.
Methane is the main part of natural gas.
Alkanes are practically insoluble in water, because their molecules are low-polar and do not interact with water molecules, but they dissolve well in non-polar organic solvents such as benzene, carbon tetrachloride. Liquid alkanes mix easily with each other.
4.Methane production.
1) With sodium acetate:
2) Synthesis from carbon and hydrogen (400-500 and high blood pressure):
3) With aluminum carbide (in vitro):
4) Hydrogenation (addition of hydrogen) of unsaturated hydrocarbons:
5) Würz reaction, which serves to increase the carbon chain: 
5. Methane chemical properties:
1) Do not enter into addition reactions.
2) Lights up:
3) Decompose when heated:
4) React halogenation
(substitution reactions):
5) When heated and under the action of catalysts, cracking- hemolytic rupture of C-C bonds. In this case, alkanes and lower alkanes are formed, for example:
6) Acetylene is formed during the dehydrogenation of methane and ethylene:
7) Combustion: - with a sufficient amount of oxygen, carbon dioxide and water:
- at insufficient quantity oxygen is formed carbon monoxide and water:
- or carbon and water:
A mixture of methane and air is explosive.
8) Thermal decomposition without oxygen to carbon and hydrogen:
6.Application of alkanes:
Methane in large quantities consumed as fuel. Hydrogen, acetylene, and soot are obtained from it. It is used in organic synthesis, in particular for the production of formaldehyde, methanol, formic acid, and other synthetic products.
At normal conditions the first four members of the homologous series of alkanes are gases.
Normal alkanes from pentane to heptadecane are liquids, and above are solids. As the number of atoms in the chain increases, i.e. with an increase in the relative molecular weight, the boiling and melting points of alkanes increase.
The lower members of the homologous series are used to obtain the corresponding unsaturated compounds by the dehydrogenation reaction. A mixture of propane and butane is used as a household fuel. The middle members of the homologous series are used as solvents and motor fuels.
Of great industrial importance is the oxidation of higher saturated hydrocarbons - paraffins with the number of carbon atoms 20-25. In this way, synthetic fatty acid with different chain lengths, which are used for the production of soaps, various detergents, lubricants, varnishes and enamels.
Liquid hydrocarbons are used as fuel (they are part of gasoline and kerosene). Alkanes are widely used in organic synthesis.
Knowledge control:
1. What compounds are called saturated?
2. Which nomenclatures do you know? What is their essence?
3. What are isomers? Give examples.
4. What is a structural formula?
5. Write down the sixth representative of alkanes.
6. What is the homological series and the homological difference.
7. What are the rules that are used when naming connections.
8. Determine the formula of paraffin, 5.6 g of which (n. At.) Have a mass of 11 g.
HOMEWORK:
Work through: P1. P. 25-34, retelling of the lecture notes №9.
Lecture number 10.
Theme: Alkenes. Ethylene, its production (by dehydrogenation of ethane and dehydration of ethanol). Ethylene chemical properties: combustion, qualitative reactions ( bleaching bromine water and potassium permanganate solution), hydration, polymerization. Polyethylene , its properties and applications. Ethylene application based on properties.
Alkyne. Acetylene, its production by pyrolysis of methane and by the carbide method. Chemical properties of acetylene: combustion, discoloration of bromine water, addition of hydrogen chloride and hydration. Acetylene application based on properties. Reaction polymerization of vinyl chloride. Polyvinyl chloride and its application.
Basic concepts and terms on the topic: alkenes and alkynes, homologous series, cracking, homologues, homologous difference, structure of alkenes and alkynes: type of hybridization.
Study plan of the topic
(list of questions required for study):
1 Unsaturated hydrocarbons: composition.
2. Physical properties of ethylene and acetylene.
3.Structure.
4. Isomerism of alkenes and alkynes.
5. Obtaining unsaturated hydrocarbons.
6. Chemical properties.
1.Unsaturated hydrocarbons: composition:
General formula hydrocarbons СnH 2 n and СnH 2 n -2, in the molecules of which there is a double bond or a triple bond between the carbon atoms, are called unsaturated. Hydrocarbons with a double bond belong to the unsaturated series of ethylene (called ethylene hydrocarbons, or alkenes), with a triple - a series of acetylene.
2.Physical properties of ethylene and acetylene:
Ethylene and acetylene are colorless gases. They are poorly soluble in water, but well in gasoline, ether and other non-polar solvents. The boiling point is the higher, the greater their molecular weight. Compared to alkanes, alkynes have higher boiling points. The density of alkynes is less than that of water.
3.Structure of unsaturated hydrocarbons:
Let's depict the structure of ethylene and acetylene molecules structurally. If carbon is considered tetravalent, then proceeding from molecular formula ethylene, not all valencies are in demand, and acetylene has four extra bonds. Let's depict structural formulas of these molecules:
A carbon atom spends two electrons to form a double bond, and three electrons to a triple bond. In the formula, this is indicated as two or three dots. Each dash is a pair of electrons.
electronic formula.
It has been experimentally proved that in a molecule with a double bond, one of them breaks relatively easily, respectively, with a triple bond, two bonds are easily broken. We can demonstrate this by experience.
Demonstration of experience:
1. A mixture of alcohol with H 2 SO 4 is heated in a test tube with sand. We pass the gas through the KMnO 4 solution, then ignite it.
Discoloration of the solution occurs due to the attachment of atoms at the site of the breaking of multiple bonds.
3СН 2 = СН 2 + 2КМnO 4 + 4H 2 O → 2MnO 2 + 3C 2 H 4 (OH) 2 + 2KOH
The electrons that form multiple bonds, at the moment of interaction with KMnO 4, are evaporated, unpaired electrons are formed, easily interconnecting with other atoms with unpaired electrons.
Ethylene and acetylene are the first in the homologous series of alkenes and alkynes.
Ethen. On a flat horizontal surface, which demonstrates the plane of overlapping of hybrid clouds (σ - bonds) lie 5 σ - bonds. Perpendicular to this surface lie P-clouds, non-hybrid, they form one π-bond.
Etin. This molecule has two π -bonds, which lie in a plane perpendicular to the plane of σ -bonds and mutually perpendicular to each other. π-bonds are fragile, because have a small overlap area.
4.Isomerism of alkenes and alkynes.
In unsaturated hydrocarbons except isomerism on carbon skeleton appears the new kind isomerism - multiple bond isomerism... The multiple bond positions are indicated by a digit at the end of the hydrocarbon name.
For example:
butene-1;
butin-2.
Count the carbon atoms from the other side to which the multiple bond is closer.
For example:
4-methylpentene-1
For alkenes and alkynes, isomerism depends on the position of the multiple bond and the structure of the carbon chain. Therefore, in the name, the number should indicate the position of the side chains and the position of the multiple bond.
isomerism of the multiple bond: CH3-CH2-CH = CH2 CH3-CH = CH-CH3
butene-1 butene-2
For unsaturated hydrocarbons, spatial or stereoisomerism is characteristic. It is called cis-, trans-isomerism.
Think about which of these compounds might have an isomer.
Cystransisomerism occurs only if each carbon atom in a multiple bond is connected to different atoms or groups of atoms. Therefore, in the chloroethene molecule (1), no matter how we rotate the chlorine atom, the molecule will be the same. Another thing is in the dichloroethene molecule (2), where the position of chlorine atoms relative to the multiple bond can be different.
The physical properties of a hydrocarbon depend not only on the quantitative composition of the molecule, but also on its structure.
Thus, the cis isomer of 2 - butene has a melting point of 138 ° C, and its trans isomer - 105.5 ° C.
Ethen and etin: industrial methods for their production are associated with the dehydrogenation of saturated hydrocarbons.
5.Production of unsaturated hydrocarbons:
1. Cracking of petroleum products . In the process of thermal cracking of saturated hydrocarbons, along with the formation of alkanes, the formation of alkenes occurs.
2.Dehydrogenation saturated hydrocarbons. When passing alkanes over the catalyst at high temperature(400-600 ° C), the hydrogen molecule is split off and an alkene is formed:
3.Dehydration with pirates (splitting off water). Impact of dehydrating agents (H2804, Al203) on monohydric alcohols at high temperatures leads to the splitting off of a water molecule and the formation of a double bond:
This reaction is called intramolecular dehydration (as opposed to intermolecular dehydration, which leads to the formation of ethers)
4.Dehydrohalogenation e(elimination of hydrogen halide).
When a haloalkane interacts with an alkali in an alcoholic solution, a double bond is formed as a result of the elimination of a hydrogen halide molecule. The reaction takes place in the presence of catalysts (platinum or nickel) and with heating. Depending on the degree of dehydrogenation, alkenes or alkynes can be obtained, as well as a transition from alkenes to alkynes: 
Note that this reaction predominantly produces 2-butene rather than 1-butene, which corresponds to according to the Zaitsev rule: Hydrogen in decomposition reactions is split off from that Carbon atom, which has the smallest number of Hydrogen atoms:
(Hydrogen is split off from, but not from).
5. Dehalogenation.
Under the action of zinc on the dibromo derivative of an alkane, the halogen atoms located at the adjacent carbon atoms are cleaved off, and a double bond is formed:
6. In industry, acetylene is mainly obtained thermal decomposition of methane:
6.Chemical properties.
The chemical properties of unsaturated hydrocarbons are primarily associated with the presence of a π - bond in the molecule... The cloud overlap region is therefore small, so it easily breaks apart, and hydrocarbons are saturated with other atoms. Addition reactions are characteristic of unsaturated hydrocarbons.
Ethylene and its homologues are characterized by reactions proceeding with the rupture of one of double connections and the addition of atoms at the point of rupture, that is, the addition reaction.
1) Combustion (with sufficient oxygen or air):
2) Hydrogenation (addition of hydrogen):
3) Halogenation (addition of halogens):
4) Hydrohalogenation (addition of hydrogen halides):
Qualitative reaction to unsaturated hydrocarbons:
1) are discoloration of bromine water or 2) potassium permanganate solution.
When bromine water interacts with unsaturated hydrocarbons, bromine is added at the site of the breaking of multiple bonds and, accordingly, the color disappears, which was due to dissolved bromine:
Markovnikov's rule
:
Hydrogen is attached to the carbon atom that is associated with a large number Hydrogen atoms... This rule can be shown on the reactions of hydration of unsymmetrical alkenes and hydrohalogenation: 
2-chloropropane
In the interaction of hydrogen halides with alkynes, the addition of the second molecule to the hydrogen halide proceeds in accordance with the Markovnikov rule:
Polymerization reactions are characteristic of unsaturated compounds.
Polymerization is a sequential connection of molecules of a low molecular weight substance with the formation of a high molecular weight substance. In this case, the connection of molecules occurs at the site of the breaking of double bonds. For example, ethene polymerization:
The polymerization product is called a polymer, and the starting material that reacts is called monomer; repeating groupings in the polymer are called structural or elementary links; the number of elementary units in a macromolecule is called degree of polymerization.
The name of the polymer is made up of the name of the monomer and the prefix poly-, for example polyethylene, polyvinyl chloride, polystyrene. Depending on the degree of polymerization of the same monomers, substances with different properties can be obtained. For example, short-chain polyethylene is a liquid that has lubricating properties. Polyethylene with a chain length of 1500-2000 links is a hard but flexible plastic material used for the manufacture of films, dishes, bottles. Polyethylene with a chain length of 5-6 thousand links is a solid substance from which cast products and pipes can be made. In the molten state, polyethylene can be formed into any shape that remains after curing. This property is called thermoplasticity.
Knowledge control:
1. What compounds are called unsaturated?
2. Display all possible isomers for a hydrocarbon with a double bond of composition C 6 H 12 and C 6 H 10. Give them names. Make an equation for the combustion reaction of pentene, pentin.
3. Solve the problem: Determine the amount of acetylene that can be obtained from calcium carbide weighing 100 g, mass fraction 0.96 if the output is 80%?
HOMEWORK:
Work through: P1. P. 43-47.49-53, L1. P. 60-65, retelling of the lecture notes No. 10.
Lecture number 11.
Theme: The unity of the chemical organization of living organisms. The chemical composition of living organisms. Alcohols. Ethanol production by glucose fermentation and ethylene hydration. Hydroxyl group as functional. The concept of hydrogen bonding. Ethanol chemical properties : combustion, interaction with sodium, the formation of simple and esters, oxidation to aldehyde. Ethanol use based on properties. Harmful impact alcohols on the human body. The concept of limit polyhydric alcohols . Glycerol as a representative of polyhydric alcohols. Qualitative reaction to polyhydric alcohols . The use of glycerin.
Aldehydes. Obtaining aldehydes by oxidation of the corresponding alcohols. Chemical properties of aldehydes: oxidation to the corresponding acid and reduction to the corresponding alcohol. Formaldehyde and Acetaldehyde Applications based on properties.
Basic concepts and terms
Example 2.2.
Write the structural formula for compound 2,4,5 trimethyl-3-ethylhexane. Write the gross formula for this compound.
1. The main (longest carbon chain) is recorded, i.e. the carbon skeleton of the alkane at the end of the proposed name is written. V this example this is hexane and all carbon atoms are numbered:
C - C - C - C - C - C
2. In accordance with the numbers indicated in the formula, all substituents are placed.
C - C - C - C - C - C
CH 3 C 2 H 5 CH 3 CH 3
3. Observing the conditions of tetravalence of carbon atoms, the remaining free valences of carbon atoms in the carbon skeleton are filled with hydrogen atoms:
CH 3 - CH - CH - CH - CH - CH 3
CH 3 C 2 H 5 CH 3 CH 3
4. The number of carbon atoms in this compound 11. The gross formula of this compound is С 11 Н 24
Isomerism of alkanes. Derivation of structural formulas of isomers.
Molecules that have the same composition but differ in different structures are called isomers. Isomers differ in chemical and physical properties.
There are several types of isomerism in organic chemistry. Limiting aliphatic hydrocarbons - alkanes have one character, the simplest type of isomerism. This type of isomerism is called structural or carbon skeleton isomerism.
In the molecules of methane, ethane and propane, there can be only one single order of joining carbon atoms:
N N N N N N
│ │ │ │ │ │
H - C - H H - C - C - H H - C - C - C - H
│ │ │ │ │ │
N N N N N N
Methane Ethane Propane
If a hydrocarbon molecule contains more than three atoms, then the order of their connection to each other can be different. For example, C 4 H 8 butane may contain two isomers: linear and branched.
Example 2.3. Compose and name all possible isomers of pentane C 5 H 12.
When deriving the structural formulas of individual isomers, one can proceed as follows.
1. According to the total number of carbon atoms in the molecule (5), I first write down a straight carbon chain - a carbon skeleton:
2. Then, "cleaving off" one extreme carbon atom, they are placed at the remaining carbons in the chain so as to obtain the maximum possible number of completely new structures. When one carbon atom is cleaved from pentane, only one more isomer can be obtained:
3. It is impossible to obtain another isomer by rearranging the carbon removed from the chain, since when rearranging it to the third carbon atom of the main chain, according to the rules for composing names, the numbering of the main chain will need to be done from right to left. By splitting off two carbon atoms from pentane, another isomer can be obtained:
4. Observing the conditions of tetravalence of carbon atoms, fill the remaining free valencies of carbon atoms in the carbon skeleton with hydrogen atoms
(see example 2.2.)
Note: it is necessary to understand that by "bending" a molecule arbitrarily, a new isomer cannot be obtained. The formation of isomers is observed only when the initial structure of the compound is disturbed. For example the below connections
C - C - C - C - C and C - C - C
are not isomers, they are the carbon skeleton of the same pentane compound.
3. CHEMICAL PROPERTIES OF LIMIT HYDROCARBONS
(tasks No. 51 - 75)
Literature:
N.L. Glinka. General chemistry. - L .: Chemistry, 1988, ch.XV, p. 164, p. 452 - 455.
Example 3.1. Using pentane as an example, characterize Chemical properties alkanes. Indicate the reaction conditions and name the reaction products.
Solution:
1. The main reactions of alkanes are reactions of hydrogen substitution proceeding by a free-radical mechanism.
1.1. Halogenation h n
CH 3 - CH 2 - CH 2 - CH 2 - C N 3 + Cl 2 ¾¾® СН 3 - СН 2 - СН 2 - СН 2 - СН 2 Сl + HСl
pentane 1-chloropentane
CH 3 - C N 2 - CH 2 - CH 2 - CH 3 + Cl 2 ¾¾® CH 3 - CH - CH 2 - CH 2 - CH 3 + HCl
2-chloropentane
CH 3 - CH 2 - C N 2 - CH 2 - CH 3 + Cl 2 ¾¾® CH 3 - CH 2 - CH - CH 2 - CH 3 + HCl
3-chloropentane
At the first stage of the reaction in the pentane molecule, the substitution of the hydrogen atom will occur at both the primary and secondary carbon atoms, as a result of which a mixture of isomeric monochloro derivatives is formed.
However, the binding energy of a hydrogen atom with a primary carbon atom is greater than with a secondary carbon atom and more than with a tertiary carbon atom, so it is easier to replace a hydrogen atom bound to a tertiary carbon atom. This phenomenon called selectivity. It is more pronounced in less active halogens (bromine, iodine). Selectivity decreases with increasing temperature.
1.2. Nitration (reaction of M.M. Konovalov)
HNO 3 = OHNO 2 Catalyst H 2 SO 4 conc.
As a result of the reaction, a mixture of nitro derivatives is formed.
t = 120-150 0 С
CH 3 - CH 2 - CH 2 - CH 2 - C N 3 + OHNO 2 ¾¾® CH 3 - CH 2 - CH 2 - CH 2 - CH 2 NO 2 + H 2 O
pentane 1-nitropentane
t = 120-150 0 С
CH 3 - C N 2 - CH 2 - CH 2 - CH 3 + OHNO 2 ¾¾® CH 3 - CH - CH 2 - CH 2 - CH 3 + H 2 O
NO 2 2-nitropentane
t = 120-150 0 С
CH 3 - CH 2 - C N 2 - CH 2 - CH 3 + OHNO 2 ¾¾® CH 3 - CH 2 - CH - CH 2 - CH 3 + H 2 O
NO 2 3-nitropentane
1.3. Sulfonation reaction Concentrated Н 2 SO 4 = ОНSO 3 Н
CH 3 - CH 2 - CH 2 - CH 2 - C N 3 + OHSO 3 H ® CH 3 - CH 2 - CH 2 - CH 2 - CH 2 SO 3 H + H 2 O
pentane 1-sulfopentane
2. Complete oxidation reaction - combustion.
С 5 Н 12 + 8 (О 2 + 3.76 N 2) ® 5СО 2 + 6Н 2 О + 8 × 3.76N 2
3. Thermal decomposition
С 5 Н 12 ® 5С + 6Н 2
4. Cracking - a cleavage reaction with the formation of alkane and alkene
CH 3 - CH 2 - CH 2 - CH 2 - CH 3 ¾¾® CH 3 - CH 3 + CH 2 = CH - CH 3
pentane ethane propene
5. Isomerization reaction
CH 3 - CH 2 - CH 2 - CH 2 - CH 3 ¾¾® CH 3 ¾ C ¾ CH 3
CH 3 2,2-dimethylpropane
Example 3.2. Describe the methods for producing alkanes. Write the reaction equations with which you can get propane.
Solution:
1. Cracking of alkanes
CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 3 ® CH 3 - CH 2 - CH 3 + CH 2 = CH - CH 3
hexane propane propene
2. Würz reaction
CH 3 - Cl + 2Na + Cl - CH 2 - CH 3 ® CH 3 - CH 2 - CH 3 + 2NaCl
chloromethane chloroethane propane
3. Reduction of halogenated alkanes
3.1. Hydrogen reduction
CH 3 - CH 2 - CH 2 - I + H - H ® CH 3 - CH 2 - CH 3 + HI
1-iodopropane hydrogen propane
3.2. Reduction with hydrogen halide
CH 3 - CH 2 - CH 2 - I + H - I ® CH 3 - CH 2 - CH 3 + I 2
1-iodopropane iodopropane iodine
fusion
CH 3 - CH 2 - CH 2 - C = O + NaOH ¾¾¾® CH 3 - CH 2 - CH 3 + Na 2 CO 3
sodium salt \ hydroxide propane carbonate
sodium butanoic acid ONa (soda)
5. Hydrogenation of unsaturated hydrocarbons
5.1. Alkenes hydrogenation
CH 2 = CH - CH 3 + H 2 ® CH 3 - CH 2 - CH 3
propene propane
5.2. Hydrogenation of alkynes
СН º С - СН 3 + 2Н 2 ® СН 3 - СН 2 - СН 3
One of the most important tasks in chemistry is the correct composition of chemical formulas. A chemical formula is a written representation of the composition of a chemical using the Latin element designation and indices. For the correct drawing up of the formula, we will definitely need Mendeleev table and knowledge simple rules... They are quite simple and even children can remember them.
How to write chemical formulas
The main concept in the preparation of chemical formulas is “ valence". Valence is the property of one element to hold a certain number of atoms in a compound. The valence of a chemical element can be viewed in the periodic table, and you also need to remember and be able to apply simple general rules.
- The valency of the metal is always equal to the group number, provided that it is in the main subgroup. For example, potassium has a valency of 1, and calcium — 2.
- Non-metals are a little more complicated. Non-metal can have higher and lower valence. The highest valency is equal to the group number. The lowest valence can be determined by subtracting the element group number from eight. When combined with metals, non-metals always have the lowest valence. Oxygen always has a valency of 2.
- In the combination of two non-metals, the lowest valency is chemical element, which is located in the periodic table to the right and above. But, fluorine always has a valency of 1.
- One more thing important rule when placing odds! The total number of valencies of one element must always be equal to the total number of valencies of another element!
Let's consolidate the knowledge gained by the example of the combination of lithium and nitrogen. Metal lithium has a valency equal to 1. Nonmetal nitrogen is located in group 5 and has a higher valency of 5 and a lower valence of 3. As we already know, in compounds with metals, nonmetals always have a lower valence, therefore nitrogen in this case will have a valency of three. We place the coefficients and get the required formula: Li 3 N.
So, quite simply, we learned how to make chemical formulas! And for better memorization of the algorithm for drawing up formulas, we have prepared its graphical representation.
