Alkanes short summary. Alkanes - nomenclature, preparation, chemical properties

Chemistry lessons in the 10th grade according to the two-hour program of Gabrielyan O.S.

Abbakumov A.V.

Lesson “Natural gas. Alkanes".

(lecture)
Lesson Objectives: consider the main natural sources of hydrocarbons in the light of two areas of their use: as an energy raw material and the basis of chemical synthesis. On this material, repeat, consolidate and generalize the knowledge gained earlier about the properties and application of saturated hydrocarbons.
Equipment: collections "Oil and oil products", "Coal and products of its processing", tables on the composition of natural and associated gases, portraits of M.V. Lomonosov, D.I. Mendeleev, N.D. Zelinsky, V.G. Shukhov.
^ Lesson progress.
I. Preparing for the lesson(check the readiness for the lesson of groups of students, equipment, class; mark absent students in the journal; report the topic and objectives of the lesson).
II. Lecture.

Lecture plan.

Natural gases and their use.
The concept of hydrocarbons.
Electronic and spatial structure of the methane molecule.
Homologous series of saturated hydrocarbons.
Isomerism and nomenclature of alkanes.
Methods for obtaining and physical properties of alkanes.
Chemical properties and application of alkanes.

1. Natural gases and their uses.

Our country ranks first in the world in terms of natural gas reserves. About 200 natural gas fields have been discovered in Russia. The vast majority of produced gas is used as fuel.

Advantages of gas over other types of fuel:

high calorific value (when burning 1 m 3 of natural gas, up to 54,400 kJ is released);
cheapness;
ecological cleanliness;
easy transportation through gas pipelines.

Thus, today natural gas is one of the best types of fuel for household and industrial (cars, metallurgical, glass and soap furnaces, etc.) needs. In addition, natural gas is a valuable and cheap raw material for the chemical industry.
^ Composition of natural gas .

The composition of natural gas from different fields is different. However, the gases of all fields contain hydrocarbons with a low relative molecular weight.

Composition of natural gas:

80-90% methane;
2-3% of its homologues (ethane, propane, butane);
low content of impurities (hydrogen sulfide, nitrogen, noble gases, carbon dioxide and water vapor).

2. The concept of hydrocarbons.

Group name organic compounds, which we are starting to study today, displays their composition.

Hydrocarbons are compounds made up of only carbon and hydrogen atoms.
Hydrocarbon classification

hydrocarbons

Cyclic (carbocyclic) Acyclic

Cyclic (carbocyclic) compounds are compounds that contain one or more cycles consisting only of carbon atoms. They, in turn, are divided into aromatic and non-aromatic.

Acyclic hydrocarbons include organic compounds whose carbon skeleton of molecules is open chains.

These chains can be formed by single bonds (alkanes), contain one double bond (alkenes), two double bonds (dienes), one triple bond (alkynes).
3. ^ Electronic and spatial structure of the methane molecule .

Today we are starting to study the first class of hydrocarbons - alkanes (saturated, paraffinic hydrocarbons).

^ Alkanes are hydrocarbons in whose molecules the atoms are linked by single bonds and which correspond to general formula WITH n H 2 n +2 .

[ Demonstration of the ratio of methane to a solution of potassium permanganate and bromine water].

The simplest representative of this class, methane, has been known to people for a very long time. It was called marsh, or mine, gas.

The carbon atom in methane is in a state of sp 3 hybridization. Carbon in this case has four equivalent hybrid orbitals, the axes of which are directed to the vertices of the tetrahedron. The angle between the axes of these orbitals is 109°28". /Image of the structure of the carbon atom in sp 3 -hybrid state /.

The electronic structure of the carbon atom determines the spatial arrangement of atoms in the methane molecule. All four C–H covalent bonds are formed by overlapping the sp 3 orbitals of the carbon atom and the s orbital of the hydrogen. All bonds in the methane molecule are of the σ type. The centers of the nuclei of hydrogen atoms lie at the vertices of a regular tetrahedron. /Demonstration of the methane molecule model/ .

Almost free rotation is possible around a single carbon-carbon bond, and alkane molecules can take on a wide variety of shapes. /Demonstration on the model of the butane molecule/ .

Carbon-carbon bonds are non-polar and poorly polarizable. The length of the C - C bond in alkanes is 0.154 nm. The C-H bond is weakly polar.

The absence of polar bonds in the molecules of saturated hydrocarbons leads to the fact that they are poorly soluble in water.
4. ^ Homologous series of saturated hydrocarbons .

Limit hydrocarbons make up the homologous series of methane.

A homologous series is a set of organic compounds that have a similar structure and properties and differ from each other in composition by one or more groups - CH 2 - (homological difference).

Representatives of the same homologous series are called homologues.

Using the example of the first four representatives, derive the general formula for alkanes:

Methane - CH 4; Ethane - C 2 H 6; Propane - C 3 H 8; Butane - C 4 H 10; Pentane - C 5 H 12.

(The general formula of alkanes is C n H 2 n +2).
5. ^ Isomerism and nomenclature of alkanes .

Alkanes are characterized by structural isomerism. Structural isomers differ from each other in the structure of the carbon skeleton.
Fundamentals of IUPAC nomenclature.

Choice of the main circuit.
Atom numbering of the main chain.
Name formation.

Depending on the number of radicals connected to the carbon atom, there are: primary, secondary, tertiary and quaternary carbon atom.
6. Methods for obtaining and physical properties of alkanes.

Cracking of petroleum products
Hydrogenation of alkenes
Salt pyrolysis carboxylic acids
Wurtz reaction

7. Chemical properties and applications of alkanes

1). Combustion reaction.

Numerous chemical reactions flow both around a person and in himself. Sometimes we just don't pay attention to these chemical phenomena. When we light gas in the kitchen or flick a lighter, drive a car or watch the tragic consequences of an explosion in a mine on TV, we are witnessing the combustion reaction of alkanes [Methane Combustion Demonstration].

Like most organic matter, saturated hydrocarbons during combustion form water vapor and carbon dioxide:

CH 4 + 2O 2 → CO 2 + 2H 2 O

When burning saturated hydrocarbons, a large number of heat, which predetermines their use as fuel.
2). ^ substitution reaction .

Remember the structure of methane. The carbon atoms have completely exhausted their valence possibilities. To get another substance from methane, you need to break the C-H bonds and replace hydrogen with another atom or group of atoms. Thus, substitution reactions are characteristic of alkanes.

׀ ׀

H−C−H + Cl−Cl → H−C−Cl + H−Cl

With a sufficient amount of halogen, the reaction continues until the formation of polysubstituted products.

Only chlorine and bromine can be used as halogen in such reactions. The reaction with fluorine proceeds with an explosion and leads to the destruction of the alkane molecule, and iodine, as a less active halogen, is not capable of such a transformation.
3). ^ decomposition reaction .

When alkanes are heated without access to air, a wide variety of transformations used in industry occur with it. When methane is heated to 1000°C, pyrolysis of methane begins - decomposition into simple substances.

CH 4
C + 2H 2

2CH 4
^ CH≡CH + 3H 2

Thus, hydrocarbons with double and triple bonds can be obtained from paraffins.

4). Dehydrogenation reaction.

For methane homologues, another practically important process is possible: the dehydrogenation reaction. This transformation takes place in the presence of a catalyst at an elevated temperature and leads to the formation of ethylene hydrocarbons.

H−S−S−N
H−S=S−H + H−H

׀ ׀

It should be noted that at room temperature saturated hydrocarbons are very inert compounds that do not interact with aggressive substances. The reactions of radical substitution (halogenation, nitration) are most typical for alkanes.

Just as the structure of a substance determines its reactivity, so properties largely determine the areas of application of compounds.

Gaseous alkanes are not only domestic and industrial fuels, but also raw materials for the chemical industry. Halogen derivatives are obtained from them, including fully fluorinated hydrocarbons (freons), which are refrigerants for domestic and industrial refrigerators and air conditioners. Made from ethane and propane unsaturated hydrocarbons and further polymeric materials. Liquid hydrocarbons are, first of all, fuel for engines of various types (a supersonic aircraft consumes up to 100 liters of kerosene per minute!), solvents, raw materials for the production of alkenes.

III. Homework:§ 3 ex. 4

Lesson summary on the topic "Alkanes" teacher

The purpose of the lesson: to introduce students to alkanes (the structure of alkane molecules, familiarization with the isomerism of saturated hydrocarbons, the nomenclature of alkanes, their physical and chemical properties, the main methods of obtaining) and identify their important role in industry.

Lesson objectives:

educational : consider the homologous series of saturated hydrocarbons, structure, physical and Chemical properties, methods of their production during the processing of natural gas, the possibility of their production from natural sources: natural and associated petroleum gases, oil and coal. Educational : develop the concept of the spatial structure of alkanes; development of cognitive interests, creative and intellectual abilities, development of independence in acquiring new knowledge using new technologies. Educational : to show the unity of the material world on the example of the genetic connection of hydrocarbons of different homologous series obtained during the processing of natural and associated petroleum gases, oil and coal.

Knowledge, skills, abilities: update the concepts: "alkanes", "general formula of alkanes", "homologues", "isomers". They will acquire knowledge of chemical concepts: "carbon skeleton", "methane", "ethane", characterize the structure and chemical properties of methane, ethane, explain the dependence of the properties of methane and ethane on their composition and structure, the most important applications of methane and ethane. They will consolidate the ability to name substances according to the international nomenclature, to determine whether organic substances belong to the class of alkanes, to explain the dependence of the properties of substances on their composition and structure.

Equipment: computer, multimedia projector, screen, presentation, table.

I. Organizing time. (Inform the purpose and topic of the lesson).

II. Learned new material.

Lesson topic: "Alkanes".

Plan for the study of alkanes.

Definition. General formula for the class of hydrocarbons. homologous series. Isomerism of alkanes. The structure of alkanes. physical properties. Ways to get. Chemical properties. Application.

1. Definition. The general class formula.

Question to the class "What are hydrocarbons?"

"These are organic compounds consisting of two elements - carbon and hydrogen."

Alkanes. (Saturated hydrocarbons. Paraffins. Saturated hydrocarbons.)

Alkanes - hydrocarbons in the molecules of which all carbon atoms are connected by single bonds (-) and have the general formula: CnH2n+2.

Exercise. Derive the alkane formula if n=3, 5, 7.

2. Homologous series.

Question to the class "What are homologues?"

- "Homologs are substances that are similar in structure and properties and differ by one or more CH2 groups."

The simplest representative of alkanes is methane CH4. The next homologue is ethane C2H6.

Mentally adding the CH2 group to ethane, say the formulas of the following homologues.

So we have a homologous series of alkanes. As you can see, the suffix "an" is common to all alkanes, and starting from the fifth homologue, the name of the alkane is formed from the Greek numeral indicating the number of carbon atoms in the molecule and the suffix "an".

Table "Homological series of alkanes".

If you mentally subtract one hydrogen atom from the formulas of saturated hydrocarbons, you get the formulas for groups of atoms with unpaired electrons, which are called radicals.

Exercise. Name the following hydrocarbons according to the systematic nomenclature.

3. Isomerism of alkanes.

Question to the class "What is isomerism?"

“Isomerism is a phenomenon in which substances have the same chemical composition, but different structure and properties.

The first three members of the homologous series of alkanes - methane, ethane, propane - do not have isomers. The fourth member, C4H10 butane, is different in that it has two isomers: straight-chain normal butane and branched-chain isobutane.

CH3–CH2–CH2–CH3(butane ) CH 3 -CH–CH 3 (2- methylpropane)

The type of isomerism in which substances differ from each other in the order of bonding of atoms in a molecule is called structural isomerism or isomerism of the carbon skeleton.

Exercise. Write semistructural formulas for all possible isomers of pentane.

4. The structure of alkanes.

Question for the class “What type of chemical bonds are present in hydrocarbon molecules?”

"Chemical bonds formed as a result of overlapping orbitals along the line connecting the centers of the nuclei of two atoms are called sigma bonds"

"Chemical bonds formed as a result of overlapping orbitals in two regions, that is, outside the line connecting the centers of the nuclei of atoms, are called pi bonds."

The carbon atom in all organic substances is in an "excited" state, that is, it has four unpaired electrons at the external level. In education chemical bond 1 s and 3 p electron orbitals are involved. As a result of their merger, 4 hybrid clouds are formed (sp3 - hybridization). Hybrid clouds are located in space, forming a spatial tetrahedral shape.

5. Physical properties.

Table "The dependence of the boiling and melting points of alkanes on molecular weight».

Homologues differ in molecular weight and therefore physical characteristics. With an increase in the number of carbon atoms in an alkane molecule (with an increase in molecular weight), in the homologous series, regular change in the physical properties of homologues(transition of quantity into quality): boiling and melting points increase, density increases.

Alkanes from CH4 to C4H10 - gases, from C5H12 to C17H36 - liquids, then - solids.

6. Receipt.

In industry, alkanes are isolated from natural sources (natural and associated gases, oil, coal).

In the laboratory, alkanes are prepared by fusing sodium acetate with solid sodium hydroxide.

1. CH3COONa + NaOH ¾® CH4 + Na2CO3

More complex alkanes are obtained by reacting halogen derivatives of saturated hydrocarbons with metallic sodium.

2. 2CH3Cl + 2Na ¾® CH3-CH3 + 2NaCl (Wurtz reaction)

7. Chemical properties.

The chemical properties of any compound are determined by its structure, i.e., the nature of its constituent atoms and the nature of the bonds between them.

1. Limit hydrocarbons burn when heated:

CH4 + 2O2 → CO2 + 2H2O

a mixture of methane and oxygen (1:2) explodes when ignited

2. Decompose when heated at 1000 ºС to simple substances:

CH4 → C+ 2H2

when heated to 1500C, acetylene is obtained from methane

2CH4 → C2H2+3H2

3. Methane chlorination:

1 stageCH4 + Cl2® CH3Cl +HCl

2 stageCH3Cl + Cl2® CH2Cl2 +HCl

3 stageCH2Cl2 + Cl2® CHCl3 + HCL

4 stageCHCl3 + Cl2® CCL4 + HCL

4. Isomerization reactions proceed when heated and in the presence of a catalyst. Pentane isomerization (with aluminum chloride)

8. Application.

Methane and its derivatives have a large practical use: as a fuel, they are raw materials for the production of organic substances, solvents, fuel for diesel and turbojet engines.

III. Consolidation.

Test on the topic ALKANE

1. The composition of alkanes reflects the general formula. . .

a) CnH2n b) CnH2n+2 c) CnH2n-2 d) СnH2n-6

Answer options (choose the correct one):

Answer_1: formula a

Answer_2: formula b

Answer_3: formula in

Answer_4: formula g

2. Which compounds belong to the homologous series of methane:

a) C2H4 b) C3H8 c) C4H10 d) C5H12 e) C7H14 ?

Answer_1: compounds a, c, d

Answer_2: compounds b, d, e

Answer_3: compounds b, c, d

Answer_4: compounds d, e

3. Which of the compounds will be obtained by heating methane without air at a temperature of 1500O

Answer_1: ethylene

Answer_2: acetylene

Answer_3: carbon dioxide

Answer_4: soot

4. What reagents can alkanes interact with:

a) Br2 (solution); b) Br2, t°; c) H2SO4 (25 °С);

d) HNO3 (sample), t°; e) KMnO4 (25 °С); e) NaOH?

Answer_1: a, b, d, e

Answer_2: b, c, e

Answer_3: a, d

Answer_4: b, d

5. What type of reaction is the interaction of chlorine with methane (in the light)

Answer_1: oxidation

Answer_2: isomerization

Answer_3: substitution

Answer_4: connections

6. What haloalkane is needed to obtain

2,5-dimethylhexane by the Wurtz reaction without side products?

Answer_1: 2-bromo-2-methylpropane

Answer_2: 2-bromopropane + 1-bromo-3-methylbutane

Answer_3: 1-bromo-2-methylpropane

Answer_4: bromoethane + 1-bromobutane

IV. Homework:

Textbook "Chemistry-10" Rudzitis, Feldman.

pp. 21-27, ex. 9.11 (p.27)

Alkanes- saturated (limiting) hydrocarbons. The representative of this class is methane ( CH 4). All subsequent saturated hydrocarbons differ by CH 2- a group that is called a homologous group, and compounds are called homologues.

General formula - WITHnH 2 n +2 .

The structure of alkanes.

Each carbon atom is in sp 3- hybridization, forms 4 σ - connections (1 S-S and 3 S-N). The shape of the molecule is in the form of a tetrahedron with an angle of 109.5°.

The bond is formed by overlapping hybrid orbitals, with the maximum area of overlap lying in space on a straight line connecting the nuclei of atoms. This is the most effective overlap, so the σ-bond is considered the strongest.

Isomerism of alkanes.

For alkanes isomerism of the carbon skeleton. Limit connections can take on various geometric shapes while maintaining the angle between the bonds. For instance,

The different positions of the carbon chain are called conformations. Under normal conditions, the conformations of alkanes freely pass into each other with the help of rotation C-C bonds, so they are often called rotational isomers. There are 2 main conformations - "inhibited" and "obscured":

Isomerism of the carbon skeleton of alkanes.

The number of isomers increases with the growth of the carbon chain. For example, butane has 2 known isomers:

For pentane - 3, for heptane - 9, etc.

If the molecule alkane subtract one proton (hydrogen atom), you get a radical:

Physical properties of alkanes.

Under normal conditions - C 1 -C 4- gases , C 5 -C 17- liquids, and hydrocarbons with more than 18 carbon atoms - solids.

As the chain grows, the boiling and melting points increase. Branched alkanes have lower boiling points than normal ones.

Alkanes insoluble in water, but readily soluble in non-polar organic solvents. Easily mix with each other.

Obtaining alkanes.

Synthetic methods for obtaining alkanes:

1. From unsaturated hydrocarbons - the "hydrogenation" reaction proceeds under the influence of a catalyst (nickel, platinum) and at a temperature:

2. From halogen derivatives - wurtz reaction: reaction of monohaloalkanes with sodium metal, resulting in alkanes with twice the number of carbon atoms in the chain:

3. From salts of carboxylic acids. When a salt interacts with an alkali, alkanes are obtained that contain 1 less carbon atom compared to the original carboxylic acid:

4. Obtaining methane. In an electric arc in a hydrogen atmosphere:

C + 2H 2 = CH 4.

In the laboratory, methane is obtained as follows:

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

Chemical properties of alkanes.

Under normal conditions, alkanes are chemically inert compounds; they do not react with concentrated sulfuric and nitric acid, with concentrated alkali, or with potassium permanganate.

Stability is explained by the strength of bonds and their non-polarity.

Compounds are not prone to bond breaking reactions (addition reaction), they are characterized by substitution.

1. Halogenation of alkanes. Under the influence of a quantum of light, radical substitution (chlorination) of the alkane begins. General scheme:

The reaction proceeds according to a chain mechanism, in which there are:

A) Circuit initiation:

B) Chain growth:

C) Open circuit:

In total, it can be represented as:

2. Nitration (Konovalov reaction) of alkanes. The reaction proceeds at 140 °C:

The reaction proceeds most easily with a tertiary carbon atom than with primary and secondary.

3. Isomerization of alkanes. Under specific conditions, alkanes of a normal structure can turn into branched ones:

4. Cracking alkanes. Under the action of high temperatures and catalysts, higher alkanes can break their bonds, forming lower alkenes and alkanes:

5. Oxidation of alkanes. Under different conditions and with different catalysts, the oxidation of an alkane can lead to the formation of alcohol, aldehyde (ketone) and acetic acid. In conditions complete oxidation the reaction proceeds to the end - to the formation of water and carbon dioxide:

The use of alkanes.

Alkanes have found wide application in industry, in the synthesis of oil, fuel, etc.

I approve:

Deputy Director

on academic work

G.G.Ismagulova

Group: 5 Date: 01/23/2017

Topic: Alkanes. Homologous series, isomers. Alkanes nomenclature. The structure of alkanes. Finding in nature and obtaining alkanes. properties of alkanes.

Goals:

- to form the ability to draw up structural formulas of organic compounds, using the construction algorithm, to establish causal relationships between the composition, structure and use of substances;

Practice using the IUPAC nomenclature for alkanes;

To acquaint students with the isomerism of limiting hydrocarbons, their physical properties and the main methods of obtaining.

Lesson type: learning lesson.

Equipment and reagents: ball-and-stick and three-dimensional models of alkane molecules, paraffin samples, liquid alkanes (pentane, hexane) gasoline,

During the classes

І. Organizing time.

ІІ. Updating knowledge and skills. Checking homework.

Frontal survey of the class on the theory of the structure of organic matter by A.M. Butlerov

Substances are divided into two large groups. Which? (organic and inorganic)

Does an organic compound contain an atom? (carbon)

Organic chemistry is…………..? (chemistry of hydrocarbons and their derivatives)

Sources of organic matter? (divided into two large groups - natural and synthetic)

What are natural organic compounds and synthetic organic substances? (natural gas, oil, coal, peat, shale, ozocerite, forestry products, cotton, agricultural products, etc.), (obtained artificially, by organic synthesis)

The main provisions of the theory of the chemical structure of A. M. Butlerova.

What are called isomers?

Are the ancestor of all organic compounds? (hydrocarbons)

What compounds are called hydrocarbons and what types of them do you know?

Aliphatic hydrocarbons are saturated and unsaturated. What are saturated and unsaturated hydrocarbons?

III. Learning new material.

Alkanes - saturated hydrocarbons, in the molecules of which carbon atoms are interconnected only by a single sigma bond and which have the general formula: CnH2n+2.

Alkanes are called paraffins, or hydrocarbons of the methane series. The first member of alkanes is methane, which is why they are called hydrocarbons of the methane series.

Alkanes are saturated hydrocarbons and contain the maximum possible number of hydrogen atoms. Each carbon atom in alkane molecules is in a state of sp3 hybridization - all 4 hybrid orbitals of the C atom are equal in shape and energy, 4 electron clouds are directed to the vertices of the tetrahedron at angles of 109 ° 28 ". Due to single bonds between C atoms, free rotation around carbon bond.The type of carbon bond is σ-bonds, the bonds are of low polarity and poorly polarizable.The length of the carbon bond is 0.154 nm.

The simplest representative of the class is methane (CH4).

According to the IUPAC nomenclature, the names of alkanes are formed using the suffix -an by adding to the corresponding root from the name of the hydrocarbon. The longest unbranched hydrocarbon chain is chosen so that largest number substituents was the minimum number in the chain. In the name of the compound, the number of the carbon atom at which the substituent group or heteroatom is located is indicated by a number, then the name of the group or heteroatom and the name of the main chain. If the groups are repeated, then list the numbers indicating their position, and the number of identical groups is indicated by the prefixes di-, tri-, tetra-. If the groups are not the same, then their names are listed in alphabetical order.

Names of alkanes.

The word "alkane" is of the same origin as "alcohol". obsolete term"paraffin" comes from the Latin parum - little, insignificant and affinis - related; paraffins have little reactivity with respect to most chemicals. Many paraffins are homologues; in the homologous series of alkanes, each subsequent member differs from the previous one by one methylene group CH 2. The term comes from the Greek homologos - corresponding, similar.

homologues- substances that have the same general formula, similar in chemical properties, but differ from each other in the composition of molecules by one or more groups of CH 2 atoms, which are called homological differences.

Isomerism of alkanes.

isomerism- substances that have the same composition of molecules (i.e. the same molecular formula), but different chemical structure and therefore have different properties. Such compounds are called isomers.

Structural isomerism is characteristic.

In the formula of an alkane molecule, the main chain is chosen - the longest.

H3C-CH2-CH2-CH-CH2-CH3

2) Then this chain is numbered from the end to which the substituent (radical) is closer. If there are several deputies, then they act in such a way that the numbers indicating their position are the smallest. Substituents are listed alphabetically.

H3C-CH-CH2-CH-CH2-CH3

The hydrocarbon is called in this order: first indicate (number) the location of the substituent, then this substituent (radical) is called, and at the end the name of the main (longest) chain is added. Thus the hydrocarbon can be named: 2-methyl-4-ethylheptane (but not 6-methyl-4-ethylheptane).

The names of the radicals are formed from the names of the corresponding hydrocarbons by replacing the suffix - anna - il.

Receipt

Methods for isolating them from natural raw materials.

natural springs alkanes

How to get

2. Petroleum gas

Natural gas

Coal

Fractional distillation.

1) rectifying gases (C 3 H 8, C 4 H 10)

2) gasoline fraction (C 5 H 12 to C 11 H 24)

3) naphtha fraction (C 8 H 18 to C 14 H 30)

4) kerosene fraction (C 12 H 26 to C 18 H 38)

5) diesel fuel (C 13 H 28 to C 19 H 36)

6) fuel oil (C 18 H 38 - C 25 H 52, C 28 H 58 - C 38 H 78)

Thermal;

Catalytic

Fractional division

gas gasoline

propane-butane mixture

dry gas

Coking

coke oven gas

coal tar

pitch water

"Synthetic methods for obtaining alkanes"

receiving	Chemistry of the reaction
Isomerization
hydrogenation
Wurtz synthesis
Decarboxylation
Hydrolysis of carbides

Physical Properties

The first four members of alkanes are gases, ranging from pentane to pentadecane (C 15 H 32) - liquids, high molecular weight alkanes, which contain 16 or more carbon atoms, are solids. At normal temperatures and with increasing pressure, propane and butane can also be in liquid state. The boiling and melting points of normal alkanes are higher than the boiling and melting points of their corresponding branched alkanes. Alkanes are non-polar compounds. They are lighter than water, immiscible with water (do not dissolve in water), and do not dissolve in other polar solvents. Liquid alkanes are good solvents and are used as solvents for many organic substances. Methane and ethane, as well as high molecular weight alkanes, are odorless, but some average representatives have a peculiar smell. Alkanes are combustible compounds.

Chemical properties

Substitution reaction: Halogenation: CH 4 + Cl 2 → CH 3 Cl + HCl (chloromethane)

CH 3 Cl + Cl 2 → CH 2 Cl 2 + HCl (dichloromethane)

CH 2 Cl 2 + Cl 2 → CHCl 3 + HCl (trichloromethane)

CHCl 3 + Cl 2 → CCl 4 + HCl (tetrachloromethane).

Nitration reaction: C 2 H 6 + HNO 3 → C 2 H 5 NO 2 + H 2 O

Decomposition reactions: CH 4 → C + 2H 2, 2CH 4 → C 2 H 2 + 3H 2

Oxidation reactions: CH 4 + 2O 2 → CO 2 + 2H 2 O

2CH 4 + O 2 → 2CO + 4H 2

catalytic oxidation methane leads to the formation of important oxygen-containing organic compounds.

2CH 4 +O 2 \u003d 2CH 3 OH

Application

IV. Fixing the topic

Write out the formulas of alkanes from the formulas of the hydrocarbons below: C 2 H 4, C 3 H 8, C 4 H 6, C 5 H 12, C 6 H 6, C 7 H 16. Name them. (Page 57 task 3)

Write, adding hydrogen atoms to the carbon skeleton, complete structural formulas of the following hydrocarbons. Name them. (p.57 task 6)

Write the structural formulas of the following alkanes: a) n - pentane; b) 2 - methylbutane; c) 2,4 - dimethylpentane; d) 3 - methyl - 4 - ethylhexane; e) trimethylmethane (p. 57 task 9)

Write the structural formulas of the following substances:

a) 2,3 - dimethylbutane,

b) 2,4 - dimethyl - 3 - ethylpentane

c) n - pentane

V. Summing up the lesson

What did you learn new in the lesson?

What was interesting?

VІ . Homework

Paragraph 2.1, 2.2, 2.3, 2.4 write a mini-report about methane and ethane

Hydrocarbons, in the molecules of which the atoms are connected by single bonds and which correspond to the general formula C n H 2 n +2.
In alkane molecules, all carbon atoms are in a state of sp 3 hybridization. This means that all four hybrid orbitals of the carbon atom are identical in shape, energy and are directed to the corners of an equilateral triangular pyramid - a tetrahedron. The angles between the orbitals are 109° 28'.

Practically free rotation is possible around a single carbon-carbon bond, and alkane molecules can take on a wide variety of shapes with angles at carbon atoms close to tetrahedral (109 ° 28 ′), for example, in a molecule n-pentane.

It is especially worth recalling the bonds in the molecules of alkanes. All bonds in the molecules of saturated hydrocarbons are single. Overlapping occurs along the axis,
connecting the nuclei of atoms, i.e., these are σ-bonds. Carbon-carbon bonds are non-polar and poorly polarizable. Length C-C connection in alkanes it is 0.154 nm (1.54 10 - 10 m). C-H bonds are somewhat shorter. The electron density is slightly shifted towards the more electronegative carbon atom, i.e. S-N connection is weakly polar.

The absence of polar bonds in the molecules of saturated hydrocarbons leads to the fact that they are poorly soluble in water and do not interact with charged particles (ions). The most characteristic of alkanes are reactions that involve free radicals.

Homologous series of methane

homologues- substances similar in structure and properties and differing by one or more CH 2 groups.

Isomerism and nomenclature

Alkanes are characterized by the so-called structural isomerism. Structural isomers differ from each other in the structure of the carbon skeleton. The simplest alkane, which is characterized by structural isomers, is butane.

Fundamentals of nomenclature

1. Selecting the main circuit. The formation of the name of a hydrocarbon begins with the definition of the main chain - the longest chain of carbon atoms in the molecule, which is, as it were, its basis.
2. Numbering of atoms of the main chain. The atoms of the main chain are assigned numbers. The numbering of atoms of the main chain starts from the end closest to the substituent (structures A, B). If the substituents are at an equal distance from the end of the chain, then the numbering starts from the end at which there are more of them (structure B). If different substituents are at an equal distance from the ends of the chain, then the numbering starts from the end to which the older one is closer (structure D). The seniority of hydrocarbon substituents is determined by the order in which the letter with which their name begins follows in the alphabet: methyl (-CH 3), then ethyl (-CH 2 -CH 3), propyl (-CH 2 -CH 2 -CH 3 ) etc.
Note that the name of the substitute is formed by replacing the suffix -an with the suffix - silt in the name of the corresponding alkane.
3. Name formation. Numbers are indicated at the beginning of the name - the numbers of carbon atoms at which the substituents are located. If there are several substituents at a given atom, then the corresponding number in the name is repeated twice separated by a comma (2,2-). After the number, a hyphen indicates the number of substituents ( di- two, three- three, tetra- four, penta- five) and the name of the substituent (methyl, ethyl, propyl). Then without spaces and hyphens - the name of the main chain. The main chain is referred to as a hydrocarbon - a member of the methane homologous series ( methane CH 4, ethane C 2 H 6, propane C 3 H 8, C 4 H 10, pentane C 5 H 12, hexane C 6 H 14, heptane C 7 H 16, octane C 8 H 18, nonan C 9 H 20, dean C 10 H 22).

Physical properties of alkanes

The first four representatives of the homologous series of methane are gases. The simplest of them is methane - a colorless, tasteless and odorless gas (the smell of "gas", having felt which, you need to call 04, is determined by the smell of mercaptans - sulfur-containing compounds specially added to methane used in household and industrial gas appliances so that people those near them could smell the leak).
Hydrocarbons of composition from C 4 H 12 to C 15 H 32 - liquids; heavier hydrocarbons are solids. The boiling and melting points of alkanes gradually increase with increasing carbon chain length. All hydrocarbons are poorly soluble in water; liquid hydrocarbons are common organic solvents.

Chemical properties of alkanes

substitution reactions.
The most characteristic of alkanes are free radical substitution reactions, during which a hydrogen atom is replaced by a halogen atom or some group. Let us present the equations of characteristic reactions halogenation:

In the case of an excess of halogen, chlorination can go further, up to the complete replacement of all hydrogen atoms by chlorine:

The resulting substances are widely used as solvents and starting materials in organic synthesis.
Dehydrogenation reaction(hydrogen splitting off).
During the passage of alkanes over the catalyst (Pt, Ni, Al 2 0 3, Cr 2 0 3) at a high temperature (400-600 ° C), a hydrogen molecule is split off and an alkene is formed:

Reactions accompanied by the destruction of the carbon chain.
All saturated hydrocarbons burn with the formation of carbon dioxide and water. Gaseous hydrocarbons mixed with air in certain proportions can explode.
1. Combustion of saturated hydrocarbons is a free radical exothermic reaction that has a very great importance when using alkanes as fuel:

V general view The combustion reaction of alkanes can be written as follows:

2. Thermal splitting of hydrocarbons.

The process proceeds according to the free radical mechanism. An increase in temperature leads to a homolytic rupture of the carbon-carbon bond and the formation of free radicals.

These radicals interact with each other, exchanging a hydrogen atom, with the formation of an alkane molecule and an alkene molecule:

Thermal splitting reactions underlie the industrial process - hydrocarbon cracking. This process is the most important stage of oil refining.

3. Pyrolysis. When methane is heated to a temperature of 1000 ° C, pyrolysis of methane begins - decomposition into simple substances:

When heated to a temperature of 1500 ° C, the formation of acetylene is possible:

4. Isomerization. When linear hydrocarbons are heated with an isomerization catalyst (aluminum chloride), substances with a branched carbon skeleton are formed:

5. Aromatization. Alkanes with six or more carbon atoms in the chain in the presence of a catalyst are cyclized to form benzene and its derivatives:

Alkanes enter into reactions that proceed according to the free radical mechanism, since all carbon atoms in alkane molecules are in a state of sp 3 hybridization. The molecules of these substances are built using covalent non-polar C-C (carbon - carbon) bonds and weakly polar C-H (carbon - hydrogen) bonds. They do not have areas with high and low electron density, easily polarizable bonds, i.e., such bonds, the electron density in which can be shifted under the influence of external factors (electrostatic fields of ions). Consequently, alkanes will not react with charged particles, since bonds in alkane molecules are not broken by a heterolytic mechanism.