Instructions
To determine the valence of atoms when drawing up structural formulas, use periodic table. A three-dimensional structural formula will help show the exact distance of atoms in a molecule.
Sources:
- structural formula of substances
- Drawing up formulas for complex compounds
Some still remember with a shudder school lessons chemistry, in which it was necessary to compose structural formulas hydrocarbons and their isomers. Meanwhile, there is nothing super complicated about this. It is enough to be guided when drawing up formulas by a certain algorithm.
Instructions
Familiarize yourself with the molecular formula of a hydrocarbon. Based on it, first compose the formula for an unbranched carbon skeleton (carbon chain).
Reduce the carbon chain by one atom. Position 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 closest to. Re-number the carbon chain starting at this end. Arrange the hydrogen atoms according to the carbons.
Determine whether it is possible to place a side branch at other carbon atoms in the chain. In case of positive conclusions, draw up formulas. If this is not possible, reduce the main carbon chain by another atom and place it as another side branch. Please note: no more than 2 side branches can be placed near one carbon.
Arrange 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 other carbons in the main chain have possible side branches. If this is possible, then make formulas possible isomers, if not, reduce the carbon chain by another atom and arrange it as a side branch. Now number the entire chain of atoms and try again formulas isomers. If there are already two side branches located at the same distance from the edges of the chain, start numbering from the edge that has more side branches.
Continue these steps until you have exhausted all the options for placing side branches.
For ease of recording chemical composition and structure chemical substance were created certain rules compiling chemical formulas using special symbols, numbers and auxiliary signs.
Instructions
Chemical formulas in writing chemical equations, schematic representation chemical processes, connections. For them, the so-called language is used, which is a set symbols, such as symbols of chemical elements, the number of atoms of each element in the substance being described, etc.
Symbols of chemical elements - one or more letters Latin alphabet, of which the first is capital. This is a schematic notation of the full name of an element, for example, Ca is calcium or lat. Calcium.
The number of atoms is expressed mathematical numbers, for example, H_2 is two hydrogen atoms.
There are several ways to write 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 as a subscript. For example, H_2O is the simplest formula of 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 represented as a subscript.
The difference between the simplest and empirical formulas is shown by the notation 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 molecule of a substance 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 surrounded by parentheses, and their number is indicated by a subscript after the parentheses. The formula also uses square brackets, which contain complex compounds of atoms (compounds with a neutral molecule, ion).
The structural formula is depicted graphically in two or three-dimensional space. Chemical bonds between atoms are depicted as lines, with atoms indicated as many times as they are involved in the connection. The formula of a substance is most clearly expressed by a three-dimensional image, which shows mutual arrangement atoms and the distance between them.
Video on the topic
Hydrocarbon is organic matter, which contains only two elements: carbon and hydrogen. It can be saturated, unsaturated with a double or triple bond, cyclic and aromatic.
Example 2.2.
Write the structural formula for the compound 2,4,5 trimethyl-3-ethylhexane. Write the gross formula for this compound.
1. The main one (the longest carbon chain) is written down, i.e. The carbon skeleton of the alkane at the end of the proposed name is written down. IN in this example this is hexane and all carbon atoms are numbered:
S – S – S – S – S – S
2. In accordance with the numbers indicated in the formula, all substituents are placed.
S - S - S - S - S - S
CH 3 C 2 H 5 CH 3 CH 3
3. Observing the conditions for the tetravalence of carbon atoms, fill the remaining free valences of carbon atoms in the carbon skeleton 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 is 11. The gross formula of this compound is C 11 H 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 from each other in chemical and physical properties.
There are several types of isomerism in organic chemistry. Saturated aliphatic hydrocarbons - alkanes - have the same 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 connection of carbon atoms:
N N N N N N
│ │ │ │ │ │
N – S – N N - S - S - N N - S - S - S - N
│ │ │ │ │ │
N N N N N N
Methane ethane propane
If a hydrocarbon molecule contains more than three atoms, then the order in which they are connected to each other may be different. For example, butane C 4 H 8 may contain two isomers: linear and branched.
Example 2.3. Compose and name everything possible isomers pentane C 5 H 12.
When deriving the structural formulas of individual isomers, you can proceed as follows.
1. According to the total number of carbon atoms in the molecule (5), I first write down the straight carbon chain - the carbon skeleton:
2. Then, “splitting off” one extreme carbon atom at a time, they are placed at the carbons remaining in the chain so as to obtain the maximum possible quantity completely new structures. When one carbon atom is removed 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 naming rules, the numbering of the main chain will need to be done from right to left. By eliminating two carbon atoms from pentane, another isomer can be obtained:
4. Observing the conditions for the tetravalence of carbon atoms, fill the remaining free valences 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, it is impossible to obtain a new isomer. The formation of isomers is observed only when the original structure of the compound is disrupted. For example, the connections below
S – S – S - S – S and S – S – S
are not isomers, they are carbon skeletons of the same pentane compound.
3. CHEMICAL PROPERTIES OF SATURATE HYDROCARBONS
(tasks no. 51 – 75)
Literature:
N.L. Glinka. general chemistry. – L.: Chemistry, 1988, chapter XV, paragraph 164, p. 452 – 455.
Example 3.1. Using pentane as an example, characterize the chemical properties of alkanes. Indicate the reaction conditions and name the reaction products.
Solution:
1. The main reactions of alkanes are hydrogen substitution reactions that occur via a free radical mechanism.
1.1. Halogenation h n
CH 3 – CH 2 – CH 2 – CH 2 – C N 3 + Cl 2 ¾¾® CH 3 – CH 2 – CH 2 – CH 2 – CH 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 + HСl
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 + HСl
3-chloropentane
At the first stage of the reaction in the pentane molecule, the replacement of the hydrogen atom will occur at both the primary and secondary carbon atoms, resulting in the formation of a mixture of isomeric monochloro derivatives.
However, the binding energy of a hydrogen atom with a primary carbon atom is greater than with a secondary carbon atom and greater than with a tertiary carbon atom, so the replacement of a hydrogen atom bonded to a tertiary carbon atom is easier. This phenomenon called selectivity. It is more pronounced in less active halogens (bromine, iodine). As the temperature increases, selectivity weakens.
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 C
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 C
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 C
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 H 2 SO 4 = OHSO 3 H
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.
C 5 H 12 + 8 (O 2 + 3.76 N 2) ® 5 CO 2 + 6 H 2 O + 8 × 3.76 N 2
3. Thermal decomposition
C 5 H 12 ® 5 C + 6 H 2
4. Cracking is a splitting reaction to form an alkane and an 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 obtaining alkanes. Write the reaction equations that can be used to obtain 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. Wurtz 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. Reduction with hydrogen
CH 3 – CH 2 – CH 2 – I + H – H ® CH 3 – CH 2 – CH 3 + HI
1-iodopropane hydrogen propane
3.2. Hydrogen halide reduction
CH 3 – CH 2 – CH 2 – I + H – I ® CH 3 – CH 2 – CH 3 + I 2
1-iodopropane iodo-propane 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
butanoic acid ONa sodium sodium (soda)
5. Hydrogenation is not saturated hydrocarbons
5.1. Hydrogenation of alkenes
CH 2 = CH – CH 3 + H 2 ® CH 3 – CH 2 – CH 3
propene propane
5.2. Hydrogenation of alkynes
CH º C – CH 3 + 2H 2 ® CH 3 – CH 2 – CH 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 substance using the Latin element designation and indices. For correct drafting formulas we will definitely need the periodic table and knowledge simple rules. They are quite simple and even children can remember them.
How to make chemical formulas
The main concept when drawing up chemical formulas is “valency”. Valency is the property of one element to hold certain number 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 valence of a metal is always equal to the group number, provided that it is in main subgroup. For example, potassium has a valency of 1, and calcium has a valency of 2.
- Non-metals are a little more complicated. A non-metal can have higher and lower valency. The highest valence is equal to the group number. The lowest valency can be determined by subtracting the element's group number from eight. When combined with metals, nonmetals always have the lowest valency. Oxygen always has a valence of 2.
- In a compound of two nonmetals, the one with the lowest valence is chemical element, which is located to the right and above in the periodic table. However, fluorine always has a valence of 1.
- One more thing important rule when setting odds! Total number The valencies of one element must always be equal to the total number of valencies of another element!
Let's consolidate the knowledge gained using the example of a compound of lithium and nitrogen. The metal lithium has a valency equal to 1. The 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, so nitrogen is in in this case will have a valence of three. We arrange the coefficients and get the required formula: Li 3 N.
So, quite simply, we learned how to compose chemical formulas! And for better memorization algorithm for formulating formulas, we have prepared a graphical representation of it.
Compiling titles organic compounds according to the structural formula.
Let's do the reverse task. Let's make up the name of an organic compound based on its structural formula. (Read the rules for naming organic compounds. Make up the name of an organic compound using the structural formula.)
4. Variety of organic compounds.
Every day the number of organic substances extracted and described by chemists increases by almost a thousand. Now there are about 20 million known ( inorganic compounds exists ten times less).
The reason for the diversity of organic compounds is the uniqueness of Carbon atoms, namely:
- fairly high valence - 4;
Ability to create single, double and triple covalent bonds;
Ability to combine with each other;
The possibility of forming linear, branched, and closed chains, which are called cycles.
Among organic substances greatest connections Carbon with Hydrogen; they are called hydrocarbons. This name comes from the old names of the elements - "carbon" and "hydrogen".
Modern classification 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 known organic substances, hydrocarbon radicals constitute the main part of the molecule.
5. Classification saturated hydrocarbons.
Organic compounds can be classified:
1) by 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, one can distinguish groups of substances 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 homologs.
Ø Homologs, arranged in increasing order of their relative molecular weight, form homologous series.
Ø Group - CH2 2, called homological difference.
An example of a homologous series can be a series of saturated hydrocarbons (alkanes). Its simplest representative is methane CH 4. Ending - en characteristic of the names of saturated hydrocarbons. Next comes 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. 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 of any subsequent homolog can be obtained by adding a homologous difference to the formula of the previous hydrocarbon.
Four S-N connections, for example, in methane, are equivalent and are located symmetrically (tetrahedral) 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 produce more strong connections. These orbitals are directed towards the vertices of the tetrahedron - such an arrangement when the orbitals are as far apart as possible from each other. These new orbitals are called sp 3
– hybridized atomic orbitals.
The most convenient nomenclature, which makes it possible to name any compounds, issystematicallyI 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 the development of organic chemistry systematic nomenclature is constantly being improved and supplemented, this is monitored by the nomenclature commission International Union theoretical and applied chemistry (International Union of Pure and Applied Chemistry - IUPAC).
Alkanes nomenclature and their derivative names the first ten members of the series of saturated hydrocarbons have already been given. To emphasize that the alkane had a straight 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 replaced - en on -il (-il). Here are relevant examples:
Knowledge control:
1. What is studied organic chemistry?
2. How to distinguish organic substances from inorganic ones?
3. Is the element responsible for organic compounds?
4. Retreat types organic reactions.
5. Write down the isomers of butane.
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 the structural formula?
10. Write down the sixth representative of alkanes.
11. How are organic compounds classified?
12. What methods of breaking a connection do you know?
13. Retreat types of organic reactions.
HOMEWORK
Work through: L1. Page 4-6 L1. Pages 8-12, retelling of lecture notes No. 8.
Lecture No. 9.
Topic: Alkanes: homologous series, isomerism and nomenclature of alkanes. Chemical properties alkanes (using the example of methane and ethane): combustion, substitution, decomposition and dehydrogenation. Applications of alkanes based on properties.
alkanes, homologous series of alkanes, cracking, homologues, homologous difference, structure of alkanes: type of hybridization - sp 3.
Topic study plan
1. Saturated hydrocarbons: composition, structure, nomenclature.
2.Types chemical reactions, characteristic of organic compounds.
3.Physical properties(using methane as an example).
4. Obtaining saturated hydrocarbons.
5. Chemical properties.
6.Use 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) are hydrocarbons in whose molecules the Carbon atoms are connected to each other by simple (single) bonds, and the valences of the carbon atoms that do not participate 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: P
- number of carbon atoms.
In the molecules of saturated hydrocarbons, carbon atoms are connected to each other by a simple (single) bond, and the remaining valences are saturated with hydrogen atoms. Alkanes are also called paraffins.
To name saturated hydrocarbons, they are mainly used systematic and rational nomenclature.
Rules for systematic nomenclature.
The general (generic) name for saturated hydrocarbons is alkanes. The names of the first four members of the homologous series of methane are trivial: methane, ethane, propane, butane. Starting from the fifth, the names are derived from 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 isostructure, their unsystematic 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 according to their seniority (from less complex to more complex). If these substituents are the same, then their number is indicated. The name is based on the word "methane":
They also have their own nomenclature 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 made up of the names of the corresponding hydrocarbons by replacing the suffix -an to suffix -il(methane - methyl, ethane - ethyl, propane - propyl, etc.).
Divalent radicals are named by replacing the suffix -an on -iliden (exception - methylene radical ==CH 2).
Trivalent radicals have the suffix -ilidin (exception - methine radical ==CH).
The table shows the names of the first five hydrocarbons, their radicals, possible isomers and their corresponding formulas.
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2.Types of chemical reactions characteristic of 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 are also possible for representatives of other homologous series.
3) Elimination reactions: Such reactions are possible for alkanes and alkenes.
4) Addition reactions:
Such reactions are possible for alkenes, alkynes, and arenes.
The simplest organic substance is methane- has the molecular formula CH 4. Methane structural formula:
Electronic formula methane:
Methane molecule has the shape of a tetrahedron: in the center there is a Carbon atom, at the vertices there are Hydrogen atoms, the compounds are directed towards 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 when plant debris rots without access to air.
Methane is the main integral part 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 and carbon tetrachloride. Liquid alkanes mix easily with each other.
4.Producing methane.
1) With sodium acetate:
2) Synthesis from carbon and hydrogen (400-500 and high blood pressure):
3) With aluminum carbide(in laboratory conditions):
4) Hydrogenation (addition of hydrogen) of unsaturated hydrocarbons:
5) Wurtz reaction, which serves to increase the carbon chain: 
5. Chemical properties of methane:
1) They do not undergo addition reactions.
2) Light up:
3) Decomposes when heated:
4) They react halogenation
(substitution reactions):
5) When heated and under the influence of catalysts, cracking- hemolytic rupture C-C connections. In this case, alkanes and lower alkanes are formed, for example:
6) When methane and ethylene are dehydrogenated, acetylene is formed:
7) Combustion:- when there is a sufficient amount of oxygen, it is formed carbon dioxide and water:
- when there is insufficient oxygen, it is formed carbon monoxide and water:
- or carbon and water:
A mixture of methane and air is explosive.
8) Thermal decomposition without access of oxygen into carbon and hydrogen:
6.Application of alkanes:
Methane in large quantities is consumed as fuel. Hydrogen, acetylene, and soot are obtained from it. It is used in organic syntheses, 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, from and above are solids. As the number of atoms in the chain increases, i.e. As the relative molecular weight increases, the boiling and melting points of alkanes increase.
The lower members of the homologous series are used to obtain the corresponding unsaturated compounds by dehydrogenation reaction. A mixture of propane and butane is used as 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 a number of carbon atoms of 20-25. In this way, synthetic fatty acids with different chain lengths are obtained, 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 the structural formula?
5. Write down the sixth representative of alkanes.
6. What is a homological series and homological difference.
7. Name the rules that are used when naming compounds.
8. Determine the formula of paraffin, 5.6 g of which (no.) have a mass of 11 g.
HOMEWORK:
Work through: L1. Page 25-34, retelling of lecture notes No. 9.
Lecture No. 10.
Topic: Alkenes. Ethylene, its preparation (dehydrogenation of ethane and dehydration of ethanol). Chemical properties of ethylene: combustion, qualitative reactions ( bleaching bromine water and potassium permanganate solution), hydration, polymerization. Polyethylene , its properties and application. Applications of ethylene based on properties.
Alkynes. Acetylene, its production by methane pyrolysis and the carbide method. Chemical properties of acetylene: combustion, bromine water discoloration, addition of hydrogen chloride and hydration. Application of acetylene 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.
Topic study plan
(list of questions required to study):
1Unsaturated hydrocarbons: composition.
2.Physical properties of ethylene and acetylene.
3.Building.
4.Isomerism of alkenes and alkynes.
5.Obtaining unsaturated hydrocarbons.
6. Chemical properties.
1.Unsaturated hydrocarbons: composition:
Hydrocarbons with general formula СnH 2 n and СnH 2 n -2, in the molecules of which there is a double bond or triple bond between the carbon atoms are called unsaturated. Hydrocarbons with double bond belong to the unsaturated series of ethylene (called ethylene hydrocarbons, or alkenes), from the triple acetylene series.
2.Physical properties of ethylene and acetylene:
Ethylene and acetylene are colorless gases. They dissolve poorly in water, but well in gasoline, ether and other non-polar solvents. The boiling point increases, the more there are molecular mass. Compared to alkanes, alkynes have higher boiling points. Alkyne Density less density water.
3.Structure of unsaturated hydrocarbons:
Let us depict the structure of the molecules of ethylene and acetylene structurally. If carbon is considered tetravalent, then based on molecular formula ethylene, not all valences are required, and acetylene has four bonds that are superfluous. Let's depict structural formulas these molecules:
A carbon atom spends two electrons to form a double bond, and three electrons to form a triple bond. In the formula this is indicated by two or three dots. Each dash is a pair of electrons.
electronic formula.
It has been experimentally proven that in a molecule with a double bond, one of them is relatively easily broken; accordingly, with a triple bond, two bonds are easily broken. We can demonstrate this experimentally.
Demonstration of experience:
1. Heat a mixture of alcohol and H 2 SO 4 in a test tube with sand. We pass the gas through the KMnO 4 solution, then set it on fire.
Discoloration of the solution occurs due to the addition of atoms at the site where multiple bonds are broken.
3CH 2 =CH 2 +2KMnO 4 +4H 2 O → 2MnO 2 +3C 2 H 4 (OH) 2 +2KOH
Electrons forming multiple bonds are paired off at the moment of interaction with KMnO 4, unpaired electrons are formed, which easily interact with other atoms with unpaired electrons.
Ethylene and acetylene are the first in homologous series alkenes and alkynes.
Ethene. On a flat horizontal surface, which demonstrates the overlap plane of hybrid clouds (σ – bonds) there are 5 σ – bonds. Non-hybrid P-clouds lie perpendicular to this surface; they form one π-bond.
Etin. This molecule has two π -connections that lie in a plane, perpendicular to the planeσ-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 By carbon skeleton appears the new kind isomerism - isomerism by multiple bond position. The position of the multiple bond is indicated by the number at the end of the hydrocarbon name.
For example:
butene-1;
butine-2.
Carbon atoms are counted on 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 position of the side chains and the position of the multiple bond should be indicated with a number.
multiple bond isomerism: CH3-CH2-CH=CH2 CH3-CH=CH-CH3
butene-1 butene-2
Unsaturated hydrocarbons are characterized by spatial or stereoisomerism. It is called cis-trans isomerism.
Think about which of these compounds may have an isomer.
Cistrans isomerism 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. The situation is different in the dichloroethene molecule (2), where the position of the chlorine atoms relative to the multiple bond can be different.
The physical properties of a hydrocarbon depend not only on quantitative composition molecule, but also on its structure.
Thus, the cis isomer of 2 butene has a melting point of 138ºС, and its trans isomer is 105.5ºС.
Ethene and ethyne: industrial methods for their production are associated with the dehydrogenation of saturated hydrocarbons.
5.Obtaining unsaturated hydrocarbons:
1. Cracking of petroleum products . During the thermal cracking of saturated hydrocarbons, along with the formation of alkanes, the formation of alkenes occurs.
2.Dehydrogenation saturated hydrocarbons. When passing alkanes over a catalyst at high temperature(400-600 °C) a hydrogen molecule is eliminated and an alkene is formed:
3.Dehydration With pirts (removal of water). The impact of water-removing agents (H2804, Al203) on monohydric alcohols at high temperatures leads to the elimination 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 reacts with an alkali in an alcohol solution, a double bond is formed as a result of the elimination of a hydrogen halide molecule. The reaction occurs in the presence of catalysts (platinum or nickel) and upon 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 produces predominantly butene-2 rather than butene-1, which corresponds to Zaitsev's rule: Hydrogen in decomposition reactions is split off from the Carbon atom that has least amount Hydrogen atoms:
(Hydrogen is split off from, but not from).
5. Dehalogenation.
When zinc acts on a dibromo derivative of an alkane, halogen atoms located at neighboring carbon atoms are eliminated and a double bond is formed:
6. In industry, acetylene is mainly produced thermal decomposition methane:
6.Chemical properties.
The chemical properties of unsaturated hydrocarbons are primarily associated with the presence of π bonds in the molecule. The area of cloud overlap in this connection is small, so it is easily broken, and the hydrocarbons are saturated with other atoms. Unsaturated hydrocarbons are characterized by addition reactions.
Ethylene and its homologues are characterized by reactions that involve the rupture of one of the double compounds and the addition of atoms at the site of the rupture, that is, addition reactions.
1) Combustion (in 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 joins at the site where multiple bonds are broken and, accordingly, the color disappears, which was caused by dissolved bromine:
Markovnikov's rule
:
Hydrogen attaches to the carbon atom that is bonded to a large number Hydrogen atoms. This rule can be demonstrated in the reactions of hydration of unsymmetrical alkenes and hydrohalogenation: 
2-chloropropane
When hydrogen halides interact with alkynes, the addition of a second halogenated molecule proceeds in accordance with Markovnikov’s rule:
Polymerization reactions are characteristic of unsaturated compounds.
Polymerization- This serial connection molecules of a low molecular weight substance to form a high molecular weight substance. In this case, the connection of molecules occurs at the site where the double bonds are broken. For example, polymerization of ethene:
The product of polymerization is called a polymer, and the starting material that reacts is called monomer; Groups that repeat in a 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 consists 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 in the manufacture of film, dishes, and bottles. Polyethylene with a chain length of 5-6 thousand links is solid, from which you can prepare cast products and pipes. In the molten state, polyethylene can be given any shape that remains after curing. This property is called thermoplasticity.
Knowledge control:
1. What compounds are called unsaturated?
2. Draw all possible isomers for a hydrocarbon with a double bond of composition C 6 H 12 and C 6 H 10. Give them names. Write an equation for the combustion reaction of pentene and pentine.
3. Solve the problem: Determine the volume of acetylene that can be obtained from calcium carbide weighing 100 g, mass fraction 0.96 if the yield is 80%?
HOMEWORK:
Work through: L1. Page 43-47,49-53, L1. Page 60-65, retelling of lecture notes No. 10.
Lecture No. 11.
Subject: Unity chemical organization living organisms. Chemical composition living organisms. Alcohols. Production of ethanol by fermentation of glucose and hydration of ethylene. Hydroxyl group as a functional group. Picture of hydrogen bond. Chemical properties of ethanol : combustion, interaction with sodium, formation of simple and esters, oxidation to aldehyde. Application of ethanol based on properties. Harmful effects alcohols on the human body. The concept of limit polyhydric alcohols . Glycerol as a representative of polyhydric alcohols. Qualitative reaction on polyhydric alcohols . Application of glycerin.
Aldehydes. Preparation of aldehydes by oxidation of the corresponding alcohols. Chemical properties of aldehydes: oxidation to the corresponding acid and reduction to the corresponding alcohol. Applications of formaldehyde and acetaldehyde based on properties.
Basic concepts and terms