Question to a psychologist 

Theory to the exam chemical properties of hydrocarbons. Properties of hydrocarbons. Getting hydrocarbons. The lesson consists of three parts

  • control work - a test in the USE format ( Appendix 6 )
  • homework - tests of real exams. ( Annex 7 )

    • The interactive part includes: tests of various types and crossword puzzles, compiled in the HotPotatoes 6 program. The use of a simulator and crossword puzzles contributes to the development of special skills, consolidation of knowledge and arouses interest among students. Materials from CD disks and the Internet (figures) were used. The lesson is designed for students of the age norm who are preparing for the Unified State Examination, its content can vary depending on the level of preparedness of students. The simulator can also be used as homework. How to print a crossword is described in the document "Explanatory Note" ( Annex 2 . Interactive/krossv-raspechatka/explanatory note.docx).

    The purpose of the lesson: checking students' knowledge on the topic: "Hydrocarbons" in order to prepare students for the exam.

    Lesson type: lesson of control, assessment and correction of students' knowledge.

    Lesson motto:"There is no talent, no genius without clearly enhanced industriousness ...". D. I. Mendeleev.

    Conduct form: control work with elements of training.

    Duration: 2 hours.

    Lesson objectives:

    • Educational: check the degree of assimilation of the basic concepts of the topic: hydrocarbons, classes of hydrocarbons; structure and chemical properties of hydrocarbons.
    • Educational: formation and development of educational competencies:
      • educational and cognitive: development of skills of independent cognitive activity; the ability to set a cognitive task, independently acquire knowledge, highlight the main thing, generalize, draw conclusions, conduct self-examination and self-assessment;
      • communicative: the ability to answer the question; ability to work with tests; organize and analyze their own activities;
      • informational: carry out material and symbolic modeling, highlight the essential features of concepts, extract the necessary information from various sources; prepare and present the results of their work; collapse and expand information (working with tables).
    • Educational: to cultivate a conscious attitude to educational work, to develop a sense of responsibility and interest in knowledge.

    Planned learning outcomes

    This lesson is aimed at repetition, generalization of knowledge on the topic: "Hydrocarbons" in accordance with the requirements of the Unified State Examination. It is assumed that students should demonstrate

    • knowledge:
      • definitions of concepts - alkanes, alkenes, alkadienes, cycloalkanes, arenes, aromatic bond, multiple bond, double bond, triple bond, hybridization, homology;
      • types of chemical reactions in organic chemistry;
      • chemical properties of hydrocarbons;
    • special skills:
      • classify hydrocarbons by composition;
      • name organic matter
      • formulate hydrocarbons;
      • determine the types and types of bonds in hydrocarbons;
      • determine the type of hybridization of carbon atoms;
      • represent models of hydrocarbon molecules;
      • characterize structural features of hydrocarbons;
      • determine the type of chemical reaction;
    • general learning skills:
      • plan and regulate their educational activities;
      • conduct a self-assessment;
      • communication skills (the ability to answer the question, work with tests, interact with other people).
      • apply knowledge in non-standard situations (computer version of testing, crossword puzzle).

    Difficulty level. The pace of the lesson is high, students have to complete many tasks of a test nature, regulate their own activities. The lesson is designed for children of the age norm, studying at the profile level program, with a sufficient level of motivation and general educational and organizational skills, requires preliminary preparation of the teacher and students. The lesson can be adjusted depending on the level of learning opportunities, student motivation and material resources. For example, in the absence of the opportunity to work in a computer class, provide students with assignments in paper form, replace visualization with an electronic presentation.

    Preparing for the lesson

    The lesson is preceded by preliminary preparation.

    1. For this lesson, the students prepared an activity "Crib". Exercise: Make a cheat sheet on the topic "Hydrocarbons". Conditions: on sheet A4, contain as much information about hydrocarbons as possible. Cheat sheets are not such a bad thing if they are done consciously. A competition for the best cheat sheet is announced! The winner will receive a prize and recognition from classmates!

    2. Route sheet students receive before the lesson (Figure 1) and enter into it the grades that they receive during the test.

    Figure 1. Route sheet

    I will receive grades for: “There is no talent, no genius without clearly enhanced industriousness…”

    D. I. Mendeleev

    Topic:"Hydrocarbons"

    Knowledge sheet 11th class student (FI)
    1. Dictation
    2. Test in the USE format
    3. Keeping a notebook
    4. Crossword on the topic "Hydrocarbons"
    5. Homework "Crib"
    I believe in you and wish you successful completion of the test!

    You can solve crossword puzzles and ask me questions
    http://orucezkaya.ucoz.ru/
    My opinion about the preparation for the test

    3. The first part of the lesson is held in the computer science room. Task 1, compiled in the HotPotatoes 6 program, is installed on the computers.

    4. Crossword puzzles are a variable part of the lesson, they are needed in order to keep students busy who quickly completed the tasks. They can be given to students as homework online or given as a printout (Crossword #1, Crossword #2). For children who work at a slow pace, they can be offered as homework.

    5. Reference material can be used electronically, but it is better to provide students with printed reference tables.

    6. Thus, for the lesson you need to print: reference 1, reference 2, test (text according to the number of students), crossword puzzles. To print crossword puzzles, you need to follow the link

    Lesson steps:

    1. Goal setting.

    2. Preparation for testing:

    a) chemical warm-up (quiz).
    b) chemical dictation ( Attachment 1 )
    c) crossword.
    d) training on the topic: "Hydrocarbons" (interactive tests in the HotPotatoes 6 program in training mode)

    3. Control work in the USE format (part A and B).

    4. Self-test. Summarizing.

    Explanations. Students simultaneously under the guidance of a teacher undergo a chemical warm-up, write a chemical dictation ( Attachment 1 ). Then the computers are trained by performing interactive tests. Only after that, students perform a control test in a printed version. Next, students check their work using a self-assessment sheet, analyze their work by filling out a control sheet.

    Lesson structure

    I. Goal setting- carried out long before the lesson, this is: the mood of the students, work with record sheets, self-assessment.

    Introduction by the teacher. Soon we have to take an exam in chemistry in the format of the exam. The peculiarity of the exam is that the tasks presented at the exam test not only knowledge of facts, but also the ability to think, compare, generalize, classify, apply knowledge in non-standard situations. It often happens that the student knows the content of the material, but answers the question incorrectly. Today we will look at different types of tests on the topic: "Hydrocarbons". Since "a lot of water has flown under the bridge since" when we studied the topic, so I suggest a little preparation before testing.

    The lesson consists of three parts:

    • preparation for testing;
    • testing;
    • self-esteem.

    Goal setting.

    The purpose of the lesson: find out how well we have learned the concepts of the topic, which is important for passing the exam. Today we have a lot of work to do and it is very important to organize your route correctly. Try to do everything! Before you is a route sheet on which all the stages of the lesson are written. Don't forget to enter the grades you get into it. I wish you all success!

    II. Activating student knowledge

    1. Warm up

    Frontal work with the class.

    Exercise. Name the substances and indicate the class to which they belong. The teacher shows cards with the formulas of hydrocarbons, the students name the substances and the class to which they belong.

    2. Do you believe - do not believe?

    The answers to the questions are the words "yes" or "no".

    Is it true that the statement

    • … that alkanes have one double bond?
    • … that benzene does not decolorize bromine water?
    • ... in organic substances predominantly covalent bonds?
    • …when acetylene is hydrated, ethylene is produced?
    • ... methane burns with a colorless (bluish) flame, and benzene with a smoky one?

    III. Checking students' knowledge

    Write the formulas of substances under the dictation of the teacher and indicate which class they belong to. The dictation is drawn up on leaflets and submitted for verification.

    2. Quiz(teacher gives small prizes).

      Mushroom pickers found a small swamp in the forest, from which bubbles of some kind of gas escaped in places. The match ignited the gas, and a faint flame began to wander through the swamp. What is this gas?

      In 1852, the German chemist F. Wöhler tried to isolate metallic calcium from limestone by calcining it with charcoal. He received a sintered mass of a grayish color, in which he did not find any signs of metal. With chagrin, Wöhler threw this mass into a dump in the yard of the laboratory. During the rain, laboratory assistants noticed that the rocky mass emits some unknown gas. What is this gas?

      In 1814, gas lighting appeared in London. Luminous gas was stored in pressurized iron cylinders. In the summer nights, the lighting was normal, and in the winter it was dim. The owners of the gas plant turned to the chemist Faraday for help. He found that in winter part of the lighting gas is collected at the bottom of the cylinder and turns into a liquid. This is how the now known benzene was discovered. What kind of gas did the British use to light the streets?

      The German alchemist, physician and visionary inventor Johann Becher experimented with sulfuric acid. In one of the experiments, he mixed up the vessels and added ethyl alcohol to sulfuric acid, which was nearby in a glass. Becher saw intense foaming and the release of an unknown gas that burned with a sooty flame. The new gas was called "oily" gas, and the product of its interaction with chlorine "oil of Dutch chemists". What gas are we talking about?

      One day Pentan went to the sauna to take a steam bath. It was hot in the sauna! And Aluminum Chloride worked there as a bath attendant, who offered Pentan a massage. Pentan agreed. And the attendant began to twist, twirl Pentan, saying: “What a twisted skeleton you have! We'll fix it now!" The attendant tried so hard that he tore off the methyl group. I was frightened by Aluminum Chloride, began to attach, and methyl attached to no place. Pentan wept: “There was Pentan, but it became ... (isopentane). What reaction are you talking about?

      What reaction did N.D. Zelinsky said that “M.I. Konovalov managed to revive the dead"?

    Teacher. We went through two stages of the lesson together. Now everyone moves independently. You need to pass a practice test (on computers):

    1. Preparation - training. I suggest you prepare for testing. We are working with task number 1, which I created especially for you in the HotPotatoes 6 program. You can use the lookup tables in an interactive or printed version.

    2. Knowledge control. Perform control work Appendix 6 , printed version).

    3. Self-test. Take a sheet of correct answers and evaluate your work.

    4. Reflection. On the back of the route sheet, write a wish to the teacher or yourself - or give a smiley face.

    5. Homework.

    1. Make an analysis of your work.

    Put the points in the table:

    Part A. Correct answer - 1 point; wrong answer - 0 points.
    Part B. Correct answer - 2 points; wrong answer - 0 points.

    If you have any doubts about the grade, check with your teacher.

    Figure 2. Self-examination and self-assessment sheet

    Surname, name of student
    Part A (0 or 1 point) Part B (0, 1 or 2 points) Sum
    points    		 % completed
    question number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
    Points
    Part A
    Part B
    Outcome
    Grade
    Praise yourself:
    Ask the teacher:
    Repeat:

    2. Complete the crossword

    AROMATIC HYDROCARBONS.

    These are cyclic hydrocarbons with three double conjugated bonds in the cycle.

    BenzeneFROM 6 H 6 - the ancestor of aromatic hydrocarbons. It was first isolated by Faraday in 1825 from lighting gas.

    Each of the six carbon atoms in its molecule is in the state sp 2 - hybridization and is linked to two adjacent carbon atoms and a hydrogen atom by three σ-bonds. The bond angles between each pair of π bonds are 120 0 .

    Thus, the skeleton of σ-bonds is a regular hexagon, in which all carbon atoms and all σ-bonds С–С and С–Н lie in the same plane.

    p-electrons of all carbon atoms form a single cyclic π-electron cloud, concentrated above and below the plane of the ring.

    All C–C bonds in benzene are equivalent, their length is 0.140 nm, which corresponds to an intermediate value between single and double.

    This means that in the benzene molecule there are no purely simple and double bonds between carbon atoms (as in the formula proposed in 1865 by the German chemist ), and they are all aligned (delocalized).

    General formula for the homologous series of benzeneC n H 2n-6(n ≥ 6).

    Substance

    Name by nomenclature

    historical name

    C 6 H 5 -CH 3

    methylbenzene

    C 6 H 5 -CH 2 -CH 3

    ethylbenzene

    CH 3 -C 6 H 4 -CH 3

    dimethylbenzene

    C 6 H 5 -CH (CH 3) 2

    isopropylbenzene

    If there are two or more radicals, their position is indicated by the numbers of the carbon atoms in the ring to which they are attached. The ring is numbered so that the numbers of radicals are the smallest.

    For disubstituted benzenes

    R-C 6 H 4 -R"

    Another way of constructing names is also used:

    ortho - (about -) substituents at adjacent carbon atoms of the ring, 1,2-;
    meta - (m -) substituents through one carbon atom (1,3-);
    pair -(P -) substituents on opposite sides of the (1,4-) ring.

    Isomerism in arenes.

    It is determined by the number of substituents, their location in the benzene ring and the possibility of isomerism of the carbon skeleton in substituents containing more than three carbon atoms.

    For an aromatic hydrocarbon FROM 8 H 10 there are 4 isomers: ortho-, meta- and para-xylenes and ethylbenzene.

    PRODUCTION OF AROMATIC HYDROCARBONS

    1. Dehydrogenation of cycloalkanes

    2. Dehydrocyclization (dehydrogenation and cyclization) of alkanes in the presence of a catalyst

    3.Trimerization of acetylene over activated charcoal reaction ):

    4.Alkylation of benzene with haloalkanes in the presence of anhydrous aluminum chloride, or alkenes:

    PHYSICAL PROPERTIES.

    Benzene and its closest homologues are colorless liquids with a characteristic odor, with a density of less than 1 g/ml. Flammable. Insoluble in water, but highly soluble in non-polar solvents. Benzene and toluene are poisonous (affect the kidneys, liver, bone marrow, blood).

    The higher arenas are solids.

    CHEMICAL PROPERTIES.

    Due to the presence delocalized -system arenas are not characterized by addition or oxidation reactions that lead to a violation of aromaticity. They are most characteristic electrophilic substitution reactions hydrogen atoms associated with the cycle -S E .

    1. REACTIONS OF ADDITION TO ARENES

    In addition reactions leading to the destruction of the aromatic structure of the benzene ring, arenes can enter with great difficulty.

    a. hydrogenation. The addition of hydrogen to benzene and its homologues occurs at elevated temperature and pressure in the presence of metal catalysts.

    b. Radical chlorination. With the radical chlorination of benzene, hexachlorocyclohexane is obtained - "hexachloran" (a means of combating harmful insects).

    2. REACTIONS OF RADICAL SUBSTITUTION OF HYDROGEN ATOMS IN SIDE CHAIN:

    In the case of benzene homologues, under the action of chlorine in the light or on heating, the reaction occurs radical substitution in side chain:

    3. Arene oxidation reactions

    Benzene is not oxidized even under the influence of strong oxidizing agents (KMnO 4 , K 2 Cr 2 O 7 , etc.). Therefore, it is often used as an inert solvent in the oxidation reactions of other organic compounds.

    Unlike benzene, its homologues are oxidized quite easily. Under the action of a solution of KMnO 4 in an acidic environment and heating in benzene homologues, only side chains are oxidized, while the carboxyl group remains from the side chain, and the rest goes into carbon dioxide:

    5 C 6 H 5 - CH 3 +6 KMnO 4 +9H 2 SO 4 5C6H5- COOH +6MnSO4 +3K2SO4 +14H2O

    5 C 6 H 5 - CH 2 - CH 3 +12 KMnO 4 +18H 2 SO 4 5C6H5- COOH +5 SO 2 +12MnSO4 +6K2SO4 +28H2O

    If oxidation occurs in a neutral solution when heated, then a salt of benzoic acid and potassium carbonate are formed:

    C 6 H 5 - CH 2 - CH 3 +4KMnO 4 C 6 H 5 - COO K+K 2 CO 3 +4MnO2 +KOH+2H2O

    4. SUBSTITUTION REACTIONS IN THE BENZENE RING

    1. Halogenation

    The replacement of the hydrogen atom in the benzene ring by a halogen occurs in the presence of catalysts AlCl 3 , AlBr 3 , FeCl 3 , etc.:

    2. Nitration

    Benzene reacts with a nitrating mixture (a mixture of concentrated nitric and sulfuric acids):

    3. Alkylation

    Substitution of a hydrogen atom in the benzene ring with an alkyl group ( alkylation) occurs under the action alkyl halides in the presence of AlCl catalysts 3 , FeBr 3 oralkenes in the presence of phosphoric acid:

    SUBSTITUTION IN alkylbenzenes

    Benzene homologues (alkylbenzenes) are more active in substitution reactions than benzene. For example, when nitrating toluene FROM 6 H 5 -CH 3 substitution of not one, but three hydrogen atoms can occur with the formation of 2,4,6-trinitrotoluene, moreover, in the ortho and para positions:

    ORIENTING ACTION OF DEPUTY

    IN THE BENZENE RING.

    If the benzene ring contains deputies , not only alkyl, but also containing other atoms (hydroxyl, amino group, nitro group, etc.), then the substitution reactions of hydrogen atoms in the aromatic system proceed in a strictly defined way, in accordance with the nature influence of the substituent on the aromatic π-system.

    Substituents are divided into two groups depending on the effect they exhibit (mesomeric or inductive): electron-donor (of the first kind) and electron-acceptor (of the second kind).

    ELECTRON DONOR SUBSTITUTES exhibit an increase in the electron density in the conjugated system.

    These include hydroxyl group -OH and amino group -NH 2 . The lone pair of electrons in these groups enters into common conjugation with the p-electron system of the benzene ring and increases the length of the conjugated system. As a result, the electron density is concentrated in ortho and para positions:

    Alkyl groups cannot participate in conjugation, but they exhibit +I-effect, under the action of which a similar redistribution of p-electron density occurs.

    Substitutes who have+I- effect or +M-effect, promote electrophilic substitution inortho and para - positions of the benzene ring and are calledsubstituents (orientants) of the first kind:

    So, toluene, containing a substituent of the first kind, is nitrated and brominated in the para- and ortho-positions:

    ELECTRONIC ACCEPTIVE SUBSTITUTES reduce the electron density in the conjugated system.

    These include nitrogroup -NO 2 , sulfo group -SO 3 H, aldehyde -CHO and carboxyl -COOH groups. These substituents form a common conjugated system with the benzene ring, but the overall electron cloud shifts towards these groups. Thus, the total electron density in the ring decreases, but it decreases least of all in meta positions :

    Fully halogenated alkyl radicals (for example, -CCl 3) show the -I effect and also contribute to a decrease in the electron density of the ring.

    Substituents with -I-effect or -M-effect direct electrophilic substitution tometa- positions of the benzene ring are calledsubstituents (orientants) of the second kind:

    Nitrobenzene containing a substituent of the second kind is nitrated and brominated in the meta position:

    STYRENE (vinylbenzene) C 8 H 8

    - a derivative of benzene, which has in its composition double bond in the side substituent, so he NOT belongs to the homologous series of arenes.

    Getting styrene:

      Dehydrogenation of ethylbenzene: C 6 H 5 -CH 2 -CH 3 - (t, cat) C 6 H 5 -CH \u003d CH 2 + H 2

      Dehydrohalogenation of phenylbromoethane:

    C 6 H 5 -CH-CH 3 +KOH - (alcohol) C 6 H 5 -CH \u003d CH 2 +KBr + H 2 O

    Styrene properties:

    Styrene exhibits properties characteristic of alkenes– reactions of addition, oxidation, polymerization.

    Addition reactions to styrene: proceed in accordance with Markovnikov's rule.

    C 6 H 5 -CH \u003d CH 2 + H 2 O C 6 H 5 -CH-CH 3

    Mild Styrene Oxidation:

    3C 6 H 5 -CH \u003d CH 2 +2 KMnO 4 + 4H 2 O 3 FROM 6 H 5 -CH-CH 2 + 2MnO2 + 2KOH

    Oh Oh phenylethylene glycol

    Hard oxidation of styrene:

    C 6 H 5 -CH \u003d CH 2 + 2KMnO 4 + 3H 2 SO 4 FROM 6 H 5 -FROMOO H+ CO 2 + 2MnSO 4 + K 2 SO 4 + 4H 2 O

    benzoic acid

    3C 6 H 5 -CH \u003d CH 2 + 10KMnO 4 -t o 3FROM 6 H 5 -FROMOO To+ 3K 2 CO 3 + 10MnO 2 + KOH + 4H 2 O

    potassium benzoate

    Styrene polymerization: as a result get polystyrene.

    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. The length of the C-C bond in alkanes 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., 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 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 G). 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, which is very important when using alkanes as a fuel:

    In general, 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.

    Chemical properties of alkanes

    Alkanes (paraffins) are non-cyclic hydrocarbons, in the molecules of which all carbon atoms are connected only by single bonds. In other words, there are no multiple, double or triple bonds in the molecules of alkanes. In fact, alkanes are hydrocarbons containing the maximum possible number of hydrogen atoms, and therefore they are called limiting (saturated).

    Due to saturation, alkanes cannot enter into addition reactions.

    Since carbon and hydrogen atoms have fairly close electronegativity, this leads to the fact that the CH bonds in their molecules are extremely low polarity. In this regard, for alkanes, reactions proceeding according to the mechanism of radical substitution, denoted by the symbol S R, are more characteristic.

    1. Substitution reactions

    In reactions of this type, carbon-hydrogen bonds are broken.

    RH + XY → RX + HY

    Halogenation

    Alkanes react with halogens (chlorine and bromine) under the action of ultraviolet light or with strong heat. In this case, a mixture of halogen derivatives with different degrees of substitution of hydrogen atoms is formed - mono-, di-tri-, etc. halogen-substituted alkanes.

    On the example of methane, it looks like this:

    By changing the halogen/methane ratio in the reaction mixture, it is possible to ensure that any particular methane halogen derivative predominates in the composition of the products.

    reaction mechanism

    Let us analyze the mechanism of the free radical substitution reaction using the example of the interaction of methane and chlorine. It consists of three stages:

    1. initiation (or chain initiation) - the process of formation of free radicals under the action of energy from the outside - irradiation with UV light or heating. At this stage, the chlorine molecule undergoes a homolytic cleavage of the Cl-Cl bond with the formation of free radicals:

    Free radicals, as can be seen from the figure above, are called atoms or groups of atoms with one or more unpaired electrons (Cl, H, CH 3 , CH 2, etc.);

    2. Chain development

    This stage consists in the interaction of active free radicals with inactive molecules. In this case, new radicals are formed. In particular, when chlorine radicals act on alkane molecules, an alkyl radical and hydrogen chloride are formed. In turn, the alkyl radical, colliding with chlorine molecules, forms a chlorine derivative and a new chlorine radical:

    3) Break (death) of the chain:

    Occurs as a result of the recombination of two radicals with each other into inactive molecules:

    2. Oxidation reactions

    Under normal conditions, alkanes are inert with respect to such strong oxidizing agents as concentrated sulfuric and nitric acids, permanganate and potassium dichromate (KMnO 4, K 2 Cr 2 O 7).

    Combustion in oxygen

    A) complete combustion with an excess of oxygen. Leads to the formation of carbon dioxide and water:

    CH 4 + 2O 2 \u003d CO 2 + 2H 2 O

    B) incomplete combustion with a lack of oxygen:

    2CH 4 + 3O 2 \u003d 2CO + 4H 2 O

    CH 4 + O 2 \u003d C + 2H 2 O

    Catalytic oxidation with oxygen

    As a result of heating alkanes with oxygen (~200 o C) in the presence of catalysts, a wide variety of organic products can be obtained from them: aldehydes, ketones, alcohols, carboxylic acids.

    For example, methane, depending on the nature of the catalyst, can be oxidized to methyl alcohol, formaldehyde, or formic acid:

    3. Thermal transformations of alkanes

    Cracking

    Cracking (from the English to crack - to tear) is a chemical process occurring at high temperature, as a result of which the carbon skeleton of alkane molecules breaks with the formation of alkene and alkane molecules with lower molecular weights compared to the original alkanes. For example:

    CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 → CH 3 -CH 2 -CH 2 -CH 3 + CH 3 -CH \u003d CH 2

    Cracking can be thermal or catalytic. For the implementation of catalytic cracking, due to the use of catalysts, significantly lower temperatures are used compared to thermal cracking.

    Dehydrogenation

    The elimination of hydrogen occurs as a result of breaking the C-H bonds; carried out in the presence of catalysts at elevated temperatures. Dehydrogenation of methane produces acetylene:

    2CH 4 → C 2 H 2 + 3H 2

    Heating methane to 1200 ° C leads to its decomposition into simple substances:

    CH 4 → C + 2H 2

    Dehydrogenation of other alkanes gives alkenes:

    C 2 H 6 → C 2 H 4 + H 2

    When dehydrogenating n-butane, butene or butene-2 ​​is formed (a mixture cis- and trance-isomers):

    Dehydrocyclization

    Isomerization

    Chemical properties of cycloalkanes

    The chemical properties of cycloalkanes with more than four carbon atoms in the cycles are generally almost identical to those of alkanes. For cyclopropane and cyclobutane, oddly enough, addition reactions are characteristic. This is due to the high tension within the cycle, which leads to the fact that these cycles tend to break. So cyclopropane and cyclobutane easily add bromine, hydrogen or hydrogen chloride:

    Chemical properties of alkenes

    1. Addition reactions

    Since the double bond in alkene molecules consists of one strong sigma bond and one weak pi bond, they are quite active compounds that easily enter into addition reactions. Alkenes often enter into such reactions even under mild conditions - in the cold, in aqueous solutions and organic solvents.

    Hydrogenation of alkenes

    Alkenes are able to add hydrogen in the presence of catalysts (platinum, palladium, nickel):

    CH 3 -CH \u003d CH 2 + H 2 → CH 3 -CH 2 -CH 3

    Hydrogenation of alkenes proceeds easily even at normal pressure and slight heating. An interesting fact is that the same catalysts can be used for the dehydrogenation of alkanes to alkenes, only the dehydrogenation process proceeds at a higher temperature and lower pressure.

    Halogenation

    Alkenes easily enter into an addition reaction with bromine both in aqueous solution and in organic solvents. As a result of the interaction, initially yellow solutions of bromine lose their color, i.e. discolor.

    CH 2 \u003d CH 2 + Br 2 → CH 2 Br-CH 2 Br

    Hydrohalogenation

    As is easy to see, the addition of a hydrogen halide to an unsymmetrical alkene molecule should theoretically lead to a mixture of two isomers. For example, when hydrogen bromide is added to propene, the following products should be obtained:

    Nevertheless, in the absence of specific conditions (for example, the presence of peroxides in the reaction mixture), the addition of a hydrogen halide molecule will occur strictly selectively in accordance with the Markovnikov rule:

    The addition of a hydrogen halide to an alkene occurs in such a way that hydrogen is attached to a carbon atom with a large number of hydrogen atoms (more hydrogenated), and a halogen is attached to a carbon atom with a smaller number of hydrogen atoms (less hydrogenated).

    Hydration

    This reaction leads to the formation of alcohols, and also proceeds in accordance with the Markovnikov rule:

    As you might guess, due to the fact that the addition of water to the alkene molecule occurs according to the Markovnikov rule, the formation of primary alcohol is possible only in the case of ethylene hydration:

    CH 2 \u003d CH 2 + H 2 O → CH 3 -CH 2 -OH

    It is by this reaction that the main amount of ethyl alcohol is carried out in the large-capacity industry.

    Polymerization

    A specific case of the addition reaction is the polymerization reaction, which, unlike halogenation, hydrohalogenation and hydration, proceeds through a free radical mechanism:

    Oxidation reactions

    Like all other hydrocarbons, alkenes burn easily in oxygen to form carbon dioxide and water. The equation for the combustion of alkenes in excess oxygen has the form:

    C n H 2n+2 + O 2 → nCO 2 + (n+1)H 2 O

    Unlike alkanes, alkenes are easily oxidized. Under the action of an aqueous solution of KMnO 4 on alkenes, decolorization, which is a qualitative reaction to double and triple CC bonds in molecules of organic substances.

    Oxidation of alkenes with potassium permanganate in a neutral or slightly alkaline solution leads to the formation of diols (dihydric alcohols):

    C 2 H 4 + 2KMnO 4 + 2H 2 O → CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH (cooling)

    In an acidic environment, the double bond is completely broken with the transformation of the carbon atoms that formed the double bond into carboxyl groups:

    5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O (heating)

    If the double C=C bond is at the end of the alkene molecule, then carbon dioxide is formed as a product of oxidation of the extreme carbon atom at the double bond. This is due to the fact that the intermediate oxidation product, formic acid, is easily oxidized by itself in an excess of an oxidizing agent:

    5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O (heating)

    In the oxidation of alkenes, in which the C atom at the double bond contains two hydrocarbon substituents, a ketone is formed. For example, the oxidation of 2-methylbutene-2 ​​produces acetone and acetic acid.

    The oxidation of alkenes, which breaks the carbon skeleton at the double bond, is used to establish their structure.

    Chemical properties of alkadienes

    Addition reactions

    For example, the addition of halogens:

    Bromine water becomes colorless.

    Under normal conditions, the addition of halogen atoms occurs at the ends of the butadiene-1,3 molecule, while π bonds are broken, bromine atoms are attached to the extreme carbon atoms, and free valences form a new π bond. Thus, as if there is a "movement" of the double bond. With an excess of bromine, one more bromine molecule can be added at the site of the formed double bond.

    polymerization reactions

    Chemical properties of alkynes

    Alkynes are unsaturated (unsaturated) hydrocarbons and therefore are capable of entering into addition reactions. Among the addition reactions for alkynes, electrophilic addition is the most common.

    Halogenation

    Since the triple bond of alkyne molecules consists of one stronger sigma bond and two weaker pi bonds, they are able to attach either one or two halogen molecules. The addition of two halogen molecules by one alkyne molecule proceeds by the electrophilic mechanism sequentially in two stages:

    Hydrohalogenation

    The addition of hydrogen halide molecules also proceeds by the electrophilic mechanism and in two stages. In both stages, the addition proceeds in accordance with the Markovnikov rule:

    Hydration

    The addition of water to alkynes occurs in the presence of ruthium salts in an acidic medium and is called the Kucherov reaction.

    As a result of the hydration of the addition of water to acetylene, acetaldehyde (acetic aldehyde) is formed:

    For acetylene homologues, the addition of water leads to the formation of ketones:

    Alkyne hydrogenation

    Alkynes react with hydrogen in two steps. Metals such as platinum, palladium, nickel are used as catalysts:

    Alkyne trimerization

    When acetylene is passed over activated carbon at high temperature, a mixture of various products is formed from it, the main of which is benzene, a product of acetylene trimerization:

    Dimerization of alkynes

    Acetylene also enters into a dimerization reaction. The process proceeds in the presence of copper salts as catalysts:

    Alkyne oxidation

    Alkynes burn in oxygen:

    C n H 2n-2 + (3n-1) / 2 O 2 → nCO 2 + (n-1) H 2 O

    The interaction of alkynes with bases

    Alkynes with a triple C≡C at the end of the molecule, unlike other alkynes, are able to enter into reactions in which the hydrogen atom in the triple bond is replaced by a metal. For example, acetylene reacts with sodium amide in liquid ammonia:

    HC≡CH + NaNH 2 → NaC≡CNa + 2NH 3,

    and also with an ammonia solution of silver oxide, forming insoluble salt-like substances called acetylenides:

    Thanks to this reaction, it is possible to recognize alkynes with a terminal triple bond, as well as to isolate such an alkyne from a mixture with other alkynes.

    It should be noted that all silver and copper acetylenides are explosive substances.

    Acetylides are able to react with halogen derivatives, which is used in the synthesis of more complex organic compounds with a triple bond:

    CH 3 -C≡CH + 2NaNH 2 → CH 3 -C≡CNa + NH 3

    CH 3 -C≡CNa + CH 3 Br → CH 3 -C≡C-CH 3 + NaBr

    Chemical properties of aromatic hydrocarbons

    The aromatic nature of the bond affects the chemical properties of benzenes and other aromatic hydrocarbons.

    A single 6pi electron system is much more stable than conventional pi bonds. Therefore, for aromatic hydrocarbons, substitution reactions are more characteristic than addition reactions. Arenes enter into substitution reactions by an electrophilic mechanism.

    Substitution reactions

    Halogenation

    Nitration

    The nitration reaction proceeds best under the action of not pure nitric acid, but its mixture with concentrated sulfuric acid, the so-called nitrating mixture:

    Alkylation

    The reaction in which one of the hydrogen atoms at the aromatic nucleus is replaced by a hydrocarbon radical:

    Alkenes can also be used instead of halogenated alkanes. Aluminum halides, ferric iron halides or inorganic acids can be used as catalysts.<

    Addition reactions

    hydrogenation

    Accession of chlorine

    It proceeds by a radical mechanism under intense irradiation with ultraviolet light:

    Similarly, the reaction can proceed only with chlorine.

    Oxidation reactions

    Combustion

    2C 6 H 6 + 15O 2 \u003d 12CO 2 + 6H 2 O + Q

    incomplete oxidation

    The benzene ring is resistant to oxidizing agents such as KMnO 4 and K 2 Cr 2 O 7 . The reaction does not go.

    Division of substituents in the benzene ring into two types:

    Consider the chemical properties of benzene homologues using toluene as an example.

    Chemical properties of toluene

    Halogenation

    The toluene molecule can be considered as consisting of fragments of benzene and methane molecules. Therefore, it is logical to assume that the chemical properties of toluene should to some extent combine the chemical properties of these two substances taken separately. In particular, this is precisely what is observed during its halogenation. We already know that benzene enters into a substitution reaction with chlorine by an electrophilic mechanism, and catalysts (aluminum or ferric iron halides) must be used to carry out this reaction. At the same time, methane is also capable of reacting with chlorine, but by a free radical mechanism, which requires irradiation of the initial reaction mixture with UV light. Toluene, depending on the conditions under which it undergoes chlorination, is able to give either substitution products of hydrogen atoms in the benzene ring - for this you need to use the same conditions as in the chlorination of benzene, or substitution products of hydrogen atoms in the methyl radical, if on it, how to act on methane with chlorine when irradiated with ultraviolet radiation:

    As you can see, the chlorination of toluene in the presence of aluminum chloride led to two different products - ortho- and para-chlorotoluene. This is due to the fact that the methyl radical is a substituent of the first kind.

    If the chlorination of toluene in the presence of AlCl 3 is carried out in excess of chlorine, the formation of trichlorine-substituted toluene is possible:

    Similarly, when toluene is chlorinated in the light at a higher chlorine / toluene ratio, dichloromethylbenzene or trichloromethylbenzene can be obtained:

    Nitration

    The substitution of hydrogen atoms for nitrogroup, during the nitration of toluene with a mixture of concentrated nitric and sulfuric acids, leads to substitution products in the aromatic nucleus, and not in the methyl radical:

    Alkylation

    As already mentioned, the methyl radical is an orientant of the first kind, therefore, its Friedel-Crafts alkylation leads to substitution products in the ortho and para positions:

    Addition reactions

    Toluene can be hydrogenated to methylcyclohexane using metal catalysts (Pt, Pd, Ni):

    C 6 H 5 CH 3 + 9O 2 → 7CO 2 + 4H 2 O

    incomplete oxidation

    Under the action of such an oxidizing agent as an aqueous solution of potassium permanganate, the side chain undergoes oxidation. The aromatic nucleus cannot be oxidized under such conditions. In this case, depending on the pH of the solution, either a carboxylic acid or its salt will be formed.

    Characteristic chemical properties of hydrocarbons: alkanes, alkenes, dienes, alkynes, aromatic hydrocarbons

    Alkanes

    Alkanes are hydrocarbons in whose molecules the atoms are linked by single bonds and which correspond to the general formula $C_(n)H_(2n+2)$.

    Homologous series of methane

    As you already know, homologues are substances that are similar in structure and properties and differ by one or more $CH_2$ groups.

    Limit hydrocarbons make up the homologous series of methane.

    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. As you already know, the simplest alkane, which is characterized by structural isomers, is butane:

    Let us consider in more detail for alkanes the basics of the IUPAC nomenclature:

    1. Choice of 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.

    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 G). 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 propyl ($—CH_2—CH_2—CH_3$), ethyl ($—CH_2—CH_3$ ) etc.

    Note that the name of the substitute is formed by replacing the suffix -en to 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 commas ($2.2-$). After the number, a hyphen indicates the number of substituents ( di- two, three- three, tetra- four, penta- five) and the name of the deputy ( methyl, ethyl, propyl). Then without spaces and hyphens - the name of the main chain. The main chain is called as a hydrocarbon - a member of the homologous series of methane ( methane, ethane, propane, etc.).

    The names of the substances whose structural formulas are given above are as follows:

    - structure A: $2$ -methylpropane;

    - Structure B: $3$ -ethylhexane;

    - Structure B: $2,2,4$ -trimethylpentane;

    - structure Г: $2$ -methyl$4$-ethylhexane.

    Physical and chemical properties of alkanes

    physical properties. 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, upon smelling which you need to call $104$, 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 $С_5Н_(12)$ to $С_(15)Н_(32)$ are 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.

    1. 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 the most typical reactions.

    Halogenation:

    $CH_4+Cl_2→CH_3Cl+HCl$.

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

    $CH_3Cl+Cl_2→HCl+(CH_2Cl_2)↙(\text"dichloromethane(methylene chloride)")$,

    $CH_2Cl_2+Cl_2→HCl+(CHСl_3)↙(\text"trichloromethane(chloroform)")$,

    $CHCl_3+Cl_2→HCl+(CCl_4)↙(\text"tetrachloromethane(carbon tetrachloride)")$.

    The resulting substances are widely used as solvents and starting materials in organic synthesis.

    2. Dehydrogenation (elimination of hydrogen). During the passage of alkanes over the catalyst ($Pt, Ni, Al_2O_3, Cr_2O_3$) at a high temperature ($400-600°C$), a hydrogen molecule is split off and an alkene is formed:

    $CH_3—CH_3→CH_2=CH_2+H_2$

    3. Reactions accompanied by the destruction of the carbon chain. All saturated hydrocarbons are burning with the formation of carbon dioxide and water. Gaseous hydrocarbons mixed with air in certain proportions can explode. The combustion of saturated hydrocarbons is a free radical exothermic reaction, which is of great importance when using alkanes as a fuel:

    $CH_4+2O_2→CO_2+2H_2O+880 kJ.$

    In general, the combustion reaction of alkanes can be written as follows:

    $C_(n)H_(2n+2)+((3n+1)/(2))O_2→nCO_2+(n+1)H_2O$

    Thermal breakdown of hydrocarbons:

    $C_(n)H_(2n+2)(→)↖(400-500°C)C_(n-k)H_(2(n-k)+2)+C_(k)H_(2k)$

    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:

    $R—CH_2CH_2:CH_2—R→R—CH_2CH_2+CH_2—R$.

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

    $R—CH_2CH_2+CH_2—R→R—CH=CH_2+CH_3—R$.

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

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

    $CH_4(→)↖(1000°C)C+2H_2$

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

    $2CH_4(→)↖(1500°C)CH=CH+3H_2$

    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:

    What is the reason that alkanes enter into reactions proceeding according to the free radical mechanism? All carbon atoms in alkane molecules are in the $sp^3$ hybridization state. The molecules of these substances are built using covalent nonpolar $C—C$ (carbon—carbon) bonds and weakly polar $C—H$ (carbon—hydrogen) bonds. They do not contain 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). Therefore, alkanes will not react with charged particles, because bonds in alkane molecules are not broken by a heterolytic mechanism.

    Alkenes

    Unsaturated hydrocarbons include hydrocarbons containing multiple bonds between carbon atoms in molecules. Unlimited are alkenes, alkadienes (polyenes), alkynes. Cyclic hydrocarbons containing a double bond in the cycle (cycloalkenes), as well as cycloalkanes with a small number of carbon atoms in the cycle (three or four atoms) also have an unsaturated character. The property of unsaturation is associated with the ability of these substances to enter into addition reactions, primarily hydrogen, with the formation of saturated, or saturated, hydrocarbons - alkanes.

    Alkenes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, one double bond between carbon atoms and corresponding to the general formula $C_(n)H_(2n)$.

    Its second name olefins- alkenes were obtained by analogy with unsaturated fatty acids (oleic, linoleic), the remains of which are part of liquid fats - oils (from lat. oleum- oil).

    Homologous series of ethene

    Unbranched alkenes make up the homologous series of ethene (ethylene):

    $C_2H_4$ is ethene, $C_3H_6$ is propene, $C_4H_8$ is butene, $C_5H_(10)$ is pentene, $C_6H_(12)$ is hexene, etc.

    Isomerism and nomenclature

    For alkenes, as well as for alkanes, structural isomerism is characteristic. Structural isomers differ from each other in the structure of the carbon skeleton. The simplest alkene, which is characterized by structural isomers, is butene:

    A special type of structural isomerism is the double bond position isomerism:

    $CH_3—(CH_2)↙(butene-1)—CH=CH_2$ $CH_3—(CH=CH)↙(butene-2)—CH_3$

    Almost free rotation of carbon atoms is possible around a single carbon-carbon bond, so alkane molecules can take on a wide variety of shapes. Rotation around the double bond is impossible, which leads to the appearance of another type of isomerism in alkenes - geometric, or cis-trans isomerism.

    cis- isomers are different from trance- isomers by the spatial arrangement of fragments of the molecule (in this case, methyl groups) relative to the $π$-bond plane, and, consequently, by properties.

    Alkenes are isomeric to cycloalkanes (interclass isomerism), for example:

    The nomenclature of alkenes developed by IUPAC is similar to the nomenclature of alkanes.

    1. Choice of 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 a molecule. In the case of alkenes, the main chain must contain a double bond.

    2. Atom numbering of the main chain.

    The numbering of the atoms of the main chain starts from the end to which the double bond is closest. For example, the correct connection name is:

    $5$-methylhexene-$2$, not $2$-methylhexene-$4$, as might be expected.

    If it is impossible to determine the beginning of the numbering of atoms in the chain by the position of the double bond, then it is determined by the position of the substituents, just as for saturated hydrocarbons.

    3. Name formation.

    The names of alkenes are formed in the same way as the names of alkanes. At the end of the name indicate the number of the carbon atom at which the double bond begins, and the suffix indicating that the compound belongs to the class of alkenes - -en.

    For example:

    Physical and chemical properties of alkenes

    physical properties. The first three representatives of the homologous series of alkenes are gases; substances of the composition $C_5H_(10)$ - $C_(16)H_(32)$ are liquids; higher alkenes are solids.

    The boiling and melting points naturally increase with an increase in the molecular weight of the compounds.

    Chemical properties.

    Addition reactions. Recall that a distinctive feature of the representatives of unsaturated hydrocarbons - alkenes is the ability to enter into addition reactions. Most of these reactions proceed by the mechanism

    1. hydrogenation of alkenes. Alkenes are able to add hydrogen in the presence of hydrogenation catalysts, metals - platinum, palladium, nickel:

    $CH_3—CH_2—CH=CH_2+H_2(→)↖(Pt)CH_3—CH_2—CH_2—CH_3$.

    This reaction proceeds at atmospheric and elevated pressure and does not require high temperature, because is exothermic. With an increase in temperature on the same catalysts, the reverse reaction, dehydrogenation, can occur.

    2. Halogenation (addition of halogens). The interaction of an alkene with bromine water or a solution of bromine in an organic solvent ($CCl_4$) leads to a rapid discoloration of these solutions as a result of the addition of a halogen molecule to the alkene and the formation of dihalogen alkanes:

    $CH_2=CH_2+Br_2→CH_2Br—CH_2Br$.

    3.

    $CH_3-(CH)↙(propene)=CH_2+HBr→CH_3-(CHBr)↙(2-bromopropene)-CH_3$

    This reaction is subject to Markovnikov's rule:

    When a hydrogen halide is added to an alkene, hydrogen is attached to a more hydrogenated carbon atom, i.e. the atom at which there are more hydrogen atoms, and the halogen - to the less hydrogenated one.

    Hydration of alkenes leads to the formation of alcohols. For example, the addition of water to ethene underlies one of the industrial methods for producing ethyl alcohol:

    $(CH_2)↙(ethene)=CH_2+H_2O(→)↖(t,H_3PO_4)CH_3-(CH_2OH)↙(ethanol)$

    Note that a primary alcohol (with a hydroxo group at the primary carbon) is formed only when ethene is hydrated. When propene or other alkenes are hydrated, secondary alcohols are formed.

    This reaction also proceeds in accordance with Markovnikov's rule - the hydrogen cation is attached to the more hydrogenated carbon atom, and the hydroxo group to the less hydrogenated one.

    5. Polymerization. A special case of addition is the polymerization reaction of alkenes:

    $nCH_2(=)↙(ethene)CH_2(→)↖(UV light,R)(...(-CH_2-CH_2-)↙(polyethylene)...)_n$

    This addition reaction proceeds by a free radical mechanism.

    6. Oxidation reaction.

    Like any organic compounds, alkenes burn in oxygen to form $CO_2$ and $H_2O$:

    $CH_2=CH_2+3O_2→2CO_2+2H_2O$.

    In general:

    $C_(n)H_(2n)+(3n)/(2)O_2→nCO_2+nH_2O$

    Unlike alkanes, which are resistant to oxidation in solutions, alkenes are easily oxidized by the action of potassium permanganate solutions. In neutral or alkaline solutions, alkenes are oxidized to diols (dihydric alcohols), and hydroxyl groups are attached to those atoms between which a double bond existed before oxidation:

    Alkadienes (diene hydrocarbons)

    Alkadienes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, two double bonds between carbon atoms and corresponding to the general formula $C_(n)H_(2n-2)$.

    Depending on the mutual arrangement of double bonds, there are three types of dienes:

    - alkadienes with cumulated arrangement of double bonds:

    - alkadienes with conjugated double bonds;

    $CH_2=CH—CH=CH_2$;

    - alkadienes with isolated double bonds

    $CH_2=CH—CH_2—CH=CH_2$.

    All three types of alkadienes differ significantly from each other in structure and properties. The central carbon atom (an atom that forms two double bonds) in alkadienes with cumulated bonds is in the $sp$-hybridization state. It forms two $σ$-bonds lying on the same straight line and directed in opposite directions, and two $π$-bonds lying in perpendicular planes. $π$-bonds are formed due to unhybridized p-orbitals of each carbon atom. The properties of alkadienes with isolated double bonds are very specific, because conjugated $π$-bonds significantly affect each other.

    p-Orbitals forming conjugated $π$-bonds make up practically a single system (it is called a $π$-system), because p-orbitals of neighboring $π$-bonds partially overlap.

    Isomerism and nomenclature

    Alkadienes are characterized by both structural isomerism and cis- and trans-isomerism.

    Structural isomerism.

    — isomerism of the carbon skeleton:

    — isomerism of the position of multiple bonds:

    $(CH_2=CH—CH=CH_2)↙(butadiene-1,3)$ $(CH_2=C=CH—CH_3)↙(butadiene-1,2)$

    cis-, trans- isomerism (spatial and geometric)

    For example:

    Alkadienes are isomeric compounds of the classes of alkynes and cycloalkenes.

    When forming the name of the alkadiene, the numbers of double bonds are indicated. The main chain must necessarily contain two multiple bonds.

    For example:

    Physical and chemical properties of alkadienes

    physical properties.

    Under normal conditions, propandien-1,2, butadiene-1,3 are gases, 2-methylbutadiene-1,3 is a volatile liquid. Alkadienes with isolated double bonds (the simplest of them is pentadiene-1,4) are liquids. Higher dienes are solids.

    Chemical properties.

    The chemical properties of alkadienes with isolated double bonds differ little from those of alkenes. Alkadienes with conjugated bonds have some special features.

    1. Addition reactions. Alkadienes are capable of adding hydrogen, halogens, and hydrogen halides.

    A feature of addition to alkadienes with conjugated bonds is the ability to attach molecules both in positions 1 and 2, and in positions 1 and 4.

    The ratio of the products depends on the conditions and method of carrying out the corresponding reactions.

    2.polymerization reaction. The most important property of dienes is the ability to polymerize under the influence of cations or free radicals. The polymerization of these compounds is the basis of synthetic rubbers:

    $nCH_2=(CH—CH=CH_2)↙(butadiene-1,3)→((... —CH_2—CH=CH—CH_2— ...)_n)↙(\text"synthetic butadiene rubber")$ .

    The polymerization of conjugated dienes proceeds as 1,4-addition.

    In this case, the double bond turns out to be central in the link, and the elementary link, in turn, can take both cis-, and trance- configuration.

    Alkynes

    Alkynes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, one triple bond between carbon atoms and corresponding to the general formula $C_(n)H_(2n-2)$.

    Homologous series of ethine

    Unbranched alkynes make up the homologous series of ethyne (acetylene):

    $C_2H_2$ - ethyne, $C_3H_4$ - propyne, $C_4H_6$ - butyne, $C_5H_8$ - pentine, $C_6H_(10)$ - hexine, etc.

    Isomerism and nomenclature

    For alkynes, as well as for alkenes, structural isomerism is characteristic: isomerism of the carbon skeleton and isomerism of the position of the multiple bond. The simplest alkyne, which is characterized by structural isomers of the multiple bond position of the alkyne class, is butyne:

    $CH_3—(CH_2)↙(butyn-1)—C≡CH$ $CH_3—(C≡C)↙(butyn-2)—CH_3$

    The isomerism of the carbon skeleton in alkynes is possible, starting from pentyn:

    Since the triple bond assumes a linear structure of the carbon chain, the geometric ( cis-, trans-) isomerism is not possible for alkynes.

    The presence of a triple bond in hydrocarbon molecules of this class is reflected by the suffix -in, and its position in the chain - the number of the carbon atom.

    For example:

    Alkynes are isomeric compounds of some other classes. So, hexine (alkyne), hexadiene (alkadiene) and cyclohexene (cycloalkene) have the chemical formula $С_6Н_(10)$:

    Physical and chemical properties of alkynes

    physical properties. The boiling and melting points of alkynes, as well as alkenes, naturally increase with an increase in the molecular weight of the compounds.

    Alkynes have a specific smell. They are more soluble in water than alkanes and alkenes.

    Chemical properties.

    Addition reactions. Alkynes are unsaturated compounds and enter into addition reactions. Basically, these are reactions. electrophilic addition.

    1. Halogenation (addition of a halogen molecule). Alkyne is able to attach two halogen molecules (chlorine, bromine):

    $CH≡CH+Br_2→(CHBr=CHBr)↙(1,2-dibromoethane),$

    $CHBr=CHBr+Br_2→(CHBr_2-CHBr_2)↙(1,1,2,2-tetrabromoethane)$

    2. Hydrohalogenation (addition of hydrogen halide). The addition reaction of hydrogen halide, proceeding according to the electrophilic mechanism, also proceeds in two stages, and at both stages the Markovnikov rule is fulfilled:

    $CH_3-C≡CH+Br→(CH_3-CBr=CH_2)↙(2-bromopropene),$

    $CH_3-CBr=CH_2+HBr→(CH_3-CHBr_2-CH_3)↙(2,2-dibromopropane)$

    3. Hydration (addition of water). Of great importance for the industrial synthesis of ketones and aldehydes is the water addition reaction (hydration), which is called Kucherov's reaction:

    4. hydrogenation of alkynes. Alkynes add hydrogen in the presence of metal catalysts ($Pt, Pd, Ni$):

    $R-C≡C-R+H_2(→)↖(Pt)R-CH=CH-R,$

    $R-CH=CH-R+H_2(→)↖(Pt)R-CH_2-CH_2-R$

    Since the triple bond contains two reactive $π$ bonds, alkanes add hydrogen in steps:

    1) trimerization.

    When ethyne is passed over activated carbon, a mixture of products is formed, one of which is benzene:

    2) dimerization.

    In addition to trimerization of acetylene, its dimerization is also possible. Under the action of monovalent copper salts, vinylacetylene is formed:

    $2HC≡CH→(HC≡C-CH=CH_2)↙(\text"butene-1-yn-3(vinylacetylene)")$

    This substance is used to produce chloroprene:

    $HC≡C-CH=CH_2+HCl(→)↖(CaCl)H_2C=(CCl-CH)↙(chloroprene)=CH_2$

    polymerization of which produces chloroprene rubber:

    $nH_2C=CCl-CH=CH_2→(...-H_2C-CCl=CH-CH_2-...)_n$

    Alkyne oxidation.

    Ethine (acetylene) burns in oxygen with the release of a very large amount of heat:

    $2C_2H_2+5O_2→4CO_2+2H_2O+2600kJ$ The action of an oxy-acetylene torch is based on this reaction, the flame of which has a very high temperature (more than $3000°C$), which makes it possible to use it for cutting and welding metals.

    In air, acetylene burns with a smoky flame, because. the carbon content in its molecule is higher than in the molecules of ethane and ethene.

    Alkynes, like alkenes, decolorize acidified solutions of potassium permanganate; in this case, the destruction of the multiple bond occurs.

    Reactions characterizing the main methods for obtaining oxygen-containing compounds

    1. Hydrolysis of haloalkanes. You already know that the formation of halokenalkanes in the interaction of alcohols with hydrogen halides is a reversible reaction. Therefore, it is clear that alcohols can be obtained by hydrolysis of haloalkanes- reactions of these compounds with water:

    $R-Cl+NaOH(→)↖(H_2O)R-OH+NaCl+H_2O$

    Polyhydric alcohols can be obtained by hydrolysis of haloalkanes containing more than one halogen atom in the molecule. For example:

    2. Hydration of alkenes- the addition of water to the $π$-bond of the alkene molecule - is already familiar to you, for example:

    $(CH_2=CH_2)↙(ethene)+H_2O(→)↖(H^(+))(C_2H_5OH)↙(ethanol)$

    Hydration of propene leads, in accordance with Markovnikov's rule, to the formation of a secondary alcohol - propanol-2:

    3. Hydrogenation of aldehydes and ketones. You already know that the oxidation of alcohols under mild conditions leads to the formation of aldehydes or ketones. Obviously, alcohols can be obtained by hydrogenation (hydrogen reduction, hydrogen addition) of aldehydes and ketones:

    4. Alkene oxidation. Glycols, as already noted, can be obtained by oxidizing alkenes with an aqueous solution of potassium permanganate. For example, ethylene glycol (ethanediol-1,2) is formed during the oxidation of ethylene (ethene):

    $CH_2=CH_2+[O]+H_2O(→)↖(KMnO_4)HO-CH_2-CH_2-OH$

    5. Specific methods for obtaining alcohols. Some alcohols are obtained in ways characteristic only of them. Thus, methanol is produced in industry by the interaction of hydrogen with carbon monoxide (II) (carbon monoxide) at elevated pressure and high temperature on the surface of the catalyst (zinc oxide):

    $CO+2H_2(→)↖(t,p,ZnO)CH_3-OH$

    The mixture of carbon monoxide and hydrogen required for this reaction, also called synthesis gas ($CO + nH_2O$), is obtained by passing water vapor over hot coal:

    $C+H_2O(→)↖(t)CO+H_2-Q$

    6. Fermentation of glucose. This method of obtaining ethyl (wine) alcohol has been known to man since ancient times:

    $(C_6H_(12)O_6)↙(glucose)(→)↖(yeast)2C_2H_5OH+2CO_2$

    Methods for obtaining aldehydes and ketones

    Aldehydes and ketones can be obtained oxidation or alcohol dehydrogenation. Once again, we note that aldehydes can be obtained during the oxidation or dehydrogenation of primary alcohols, and ketones can be obtained from secondary alcohols:

    Kucherov's reaction. From acetylene, as a result of the hydration reaction, acetaldehyde is obtained, from acetylene homologs - ketones:

    When heated calcium or barium salts carboxylic acids form a ketone and a metal carbonate:

    Methods for obtaining carboxylic acids

    Carboxylic acids can be obtained by oxidation of primary alcohols of aldehydes:

    Aromatic carboxylic acids are formed during the oxidation of benzene homologues:

    Hydrolysis of various carboxylic acid derivatives also results in acids. So, during the hydrolysis of an ester, an alcohol and a carboxylic acid are formed. As mentioned above, acid-catalyzed esterification and hydrolysis reactions are reversible:

    The hydrolysis of an ester under the action of an aqueous solution of alkali proceeds irreversibly, in this case, not an acid, but its salt is formed from the ester.