They are burning.

1. Combustion in air

2. Oxidation aqueous solution permanganate (Wagner reaction)

IN neutral environment brown manganese(IV) oxide is obtained, and at the double bond organic matter two OH groups are added:

On the left is an alkene with potassium permanganate, on the right is an alkane. The organic layer (top) does not mix with the aqueous layer (bottom). On the right, the color of the permanganate has not changed. Rice. 1.

Rice. 1. Wagner reaction

3. Oxidation with acidified permanganate solution

IN acidic environment the solution becomes discolored: Mn +7 is reduced to Mn +2. Discoloration of an acidified solution of potassium permanganate is a qualitative reaction to unsaturated compounds.

5CH 2 =CH 2 + 12KMnO 4 + 18H 2 SO 4 = 12MnSO 4 + 10CO 2 + 6K 2 SO 4 + 28H 2 O.

Dependence of oxidation products on the structure of the alkene:

Radical substitution in alkenes

Propene and chlorine at high temperatures: 400-500 o C (conditions favorable to radical reactions) give a product not of addition, but of substitution.

In industry Alkenes are produced by cracking or dehydrogenation of petroleum alkanes.

Laboratory methods the preparation of alkenes is based on elimination reactions.

1. Dehalogenation

The reaction of dihaloalkanes, in the molecules of which halogen atoms are located at neighboring carbon atoms, with magnesium or zinc leads to the formation of a double bond:

CH 2 Cl-CH 2 Cl + Zn → CH 2 =CH 2 + ZnCl 2

2. Dehydrohalogenation

When haloalkanes react with a hot alcoholic alkali solution, a hydrogen halide molecule is split off and an alkene is formed:

CH 3 -CH 2 -CHCl-CH 3 + KOH alcohol. CH 3 -CH=CH-CH 3 + KCl + H 2 O

3. Dehydration

Heating alcohols with concentrated sulfuric or phosphoric acid leads to the elimination of water and the formation of an alkene.

Elimination reactions of unsymmetrical haloalkanes and alcohols often proceed according to Zaitsev's rule: The hydrogen atom is preferentially split off from the C atom that is bonded to the smallest number of H atoms.

Zaitsev's rule, like Markovnikov's rule, can be explained by comparing the stability of intermediate particles that are formed in the reaction.

Ethylene, propene and butenes are the starting materials for petrochemical synthesis, primarily for the production of plastics.

When chlorine is added to alkenes, chlorine derivatives are obtained.

CH 2 =CH-CH 3 +Cl 2 → CH 2 Cl- CHCl- CH 3 (1,2-dichloropropane)

But back in 1884, the Russian scientist M.D. Lvov. (Fig. 2) carried out the chlorination reaction of propene under more severe conditions, at t = 400 0 C. The result was a product not of the addition of chlorine, but of substitution.

CH 2 =CH-CH 3 +Cl 2 CH 2 =CH-CH 2Cl + HCl

Rice. 2. Russian scientist M.D. Lviv

The interaction of the same substances under different conditions leads to different results. This reaction is widely used to produce glycerol. Sometimes ethylene is used in vegetable stores to accelerate the ripening of fruits.

Summing up the lesson

In this lesson you covered the topic “Alkenes. Chemical properties- 2. Preparation and use of alkenes.” During the lesson, you were able to deepen your knowledge about alkenes, learned about the chemical properties of alkenes, as well as the features of the preparation and use of alkenes.

References

1. Rudzitis G.E. Chemistry. Basics general chemistry. 10th grade: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.

2. Chemistry. 10th grade. Profile level: academic. for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2008. - 463 p.

3. Chemistry. 11th grade. Profile level: academic. for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2010. - 462 p.

4. Khomchenko G.P., Khomchenko I.G. Collection of problems in chemistry for those entering universities. - 4th ed. - M.: RIA "New Wave": Publisher Umerenkov, 2012. - 278 p.

Homework

1. Nos. 12, 13 (p. 39) Rudzitis G.E., Feldman F.G. Chemistry: Organic chemistry. 10th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.

2. What reaction is qualitative to ethylene and its homologues?

3. During the chlorination of propene, can substitution rather than addition occur? What is this connected with?

Alkenes are chemically active. Their chemical properties are largely determined by the presence of a double bond. The most common reactions for alkenes are electrophilic addition and radical addition reactions. Nucleophilic addition reactions usually require the presence of a strong nucleophile and are not typical for alkenes. Alkenes easily undergo oxidation and addition reactions and are also capable of alyl radical substitution.

Addition reactions

Hydrogenation The addition of hydrogen (hydrogenation reaction) to alkenes is carried out in the presence of catalysts. Most often, crushed metals are used - platinum, nickel, palladium, etc. As a result, the corresponding alkanes (saturated hydrocarbons) are formed.

$CH_2=CH_2 + H2 → CH_3–CH_3$

Addition of halogens. Alkenes easily, under ordinary conditions, react with chlorine and bromine to form the corresponding dihaloalkanes, in which halogen atoms are located at adjacent carbon atoms.

Note 1

When alkenes interact with bromine, bromine becomes discolored to a yellow-brown color. This is one of the oldest and simplest qualitative reactions to unsaturated hydrocarbons, since alkynes and alkadienes also react similarly.

$CH_2=CH_2 + Br_2 → CH_2Br–CH_2Br$

Addition of hydrogen halides. When ethylene hydrocarbons interact with hydrogen halides ($HCl$, $HBr$), haloalkanes are formed; the direction of the reaction depends on the structure of the alkenes.

In the case of ethylene or symmetrical alkenes, the addition reaction occurs unambiguously and leads to the formation of only one product:

$CH_2=CH_2 + HBr → CH_3–CH_2Br$

In the case of unsymmetrical alkenes, the formation of two different addition reaction products is possible:

Note 2

In fact, mainly only one reaction product is formed. The pattern in the direction of such reactions was established by the Russian chemist V.V. Markovnikov in 1869 It is called Markovnikov's rule. When hydrogen halides interact with unsymmetrical alkenes, a hydrogen atom is added at the site of the cleavage of the double bond in the most hydrogenated carbon atom, that is, before it is connected to a large number hydrogen atoms.

Markovnikov formulated this rule on the basis of experimental data, and only much later did it receive a theoretical justification. Consider the reaction of propylene with hydrogen chloride.

One of the features of the $p$ bond is its ability to be easily polarized. Under the influence of the methyl group (positive inductive effect + $I$) in the propene molecule, the electron density of the $p$ bond shifts to one of the carbon atoms (= $CH_2$). As a result, a partial negative charge ($\delta -$) appears on it. A partial positive charge ($\delta +$) appears on the other carbon atom of the double bond.

This distribution of electron density in the propylene molecule determines the location of the future proton attack. This is the carbon atom of the methylene group (= $CH_2$), which carries a partial negative $\delta-$ charge. And chlorine, accordingly, attacks a carbon atom with a partial positive charge $\delta+$.

As a consequence, the main product of the reaction of propylene with hydrogen chloride is 2-chloropropane.

Hydration

Hydration of alkenes occurs in the presence of mineral acids and obeys Markovnikov's rule. The reaction products are alcohols

$CH_2=CH_2 + H_2O → CH_3–CH_2–OH$

Alkylation

The addition of alkanes to alkenes in the presence of an acid catalyst ($HF$ or $H_2SO_4$) at low temperatures leads to the formation of hydrocarbons with a higher molecular weight and is often used in industry to produce motor fuel

$R–CH_2=CH_2 + R’–H → R–CH_2–CH_2–R’$

Oxidation reactions

Oxidation of alkenes can occur, depending on the conditions and types of oxidizing reagents, both with the cleavage of the double bond and with the preservation of the carbon skeleton:

Polymerization reactions

Alkene molecules are capable of adding to each other under certain conditions with the opening of $\pi$ bonds and the formation of dimers, trimmers or high molecular weight compounds - polymers. Polymerization of alkenes can proceed either by a free radical or by a cation-anion mechanism. Acids, peroxides, metals, etc. are used as polymerization initiators. The polymerization reaction is also carried out under the influence of temperature, irradiation, and pressure. A typical example is the polymerization of ethylene to form polyethylene

$nCH_2=CH_2 → (–CH_2–CH_(2^–))_n$

Substitution reactions

Substitution reactions are not typical for alkenes. However, at high temperatures (over 400 ° C), radical addition reactions, which are reversible, are suppressed. In this case, it becomes possible to replace the hydrogen atom located in the allylic position while maintaining the double bond

$CH_2=CH–CH_3 + Cl_2 – CH_2=CH–CH_2Cl + HCl$

DEFINITION

Alkenes- unsaturated hydrocarbons, the molecules of which contain one double bond; The names of alkenes contain the suffix –ene or –ylene.

General formula homologous series alkenes (Table 2) – C n H 2n

Table 2. Homologous series of alkenes.

Hydrocarbon radicals formed from alkenes: -CH = CH 2 - vinyl and -CH 2 -CH = CH 2 - allyl.

Alkenes, starting with butene, are characterized by isomerism of the carbon skeleton:

CH 2 -C(CH 3)-CH 3 (2-methylpropene-1)

and positions of the double bond:

CH 2 = CH-CH 2 -CH 3 (butene-1)

CH 3 -C = CH-CH 3 (butene-2)

Alkenes, starting with butene-2, are characterized by geometric (cis-trans) isomerism (Fig. 1).

Rice. 1. Geometric isomers of butene-2.

Alkenes, starting with propene, are characterized by interclass isomerism with cycloalkanes. Thus, the composition of C 4 H 8 corresponds to substances of the class of alkenes and cycloalkanes - butene-1(2) and cyclobutane.

The carbon atoms in alkene molecules are in sp 2 hybridization: 3σ bonds are located in the same plane at an angle of 120 to each other, and the π bond is formed by p-electrons of neighboring carbon atoms. A double bond is a combination of σ and π bonds.

Chemical properties of alkenes

Majority chemical reactions alkenes proceed through the mechanism of electrophilic addition:

- hydrohalogenation - the interaction of alkenes with hydrogen halides (HCl, HBr), proceeding according to Markovnikov’s rule (when polar molecules like HX are added to unsymmetrical alkenes, hydrogen attaches to the more hydrogenated carbon atom at the double bond)

CH 3 -CH = CH 2 + HCl = CH 3 -CHCl-CH 3

- hydration - the interaction of alkenes with water in the presence of mineral acids (sulfuric, phosphoric) with the formation of alcohols, proceeding according to Markovnikov’s rule

CH 3 -C(CH 3) = CH 2 + H 2 O = CH 3 -C(CH 3)OH-CH 3

- halogenation - the interaction of alkenes with halogens, for example, with bromine, in which bromine water becomes discolored

CH 2 = CH 2 + Br 2 = BrCH 2 -CH 2 Br

When a mixture of an alkene and a halogen is heated to 500C, it is possible to replace the hydrogen atom of the alkene by a radical mechanism:

CH 3 -CH = CH 2 + Cl 2 = Cl-CH 2 -CH = CH 2 + HCl

The hydrogenation reaction of alkenes proceeds according to a radical mechanism. The condition for the reaction to occur is the presence of catalysts (Ni, Pd, Pt), as well as heating of the reaction mixture:

CH 2 = CH 2 + H 2 = CH 3 -CH 3

Alkenes can be oxidized to form various products, the composition of which depends on the conditions of the oxidation reaction. Thus, during oxidation under mild conditions (the oxidizing agent is potassium permanganate), the π bond is broken and dihydric alcohols are formed:

3CH 2 = CH 2 + 2KMnO 4 +4H 2 O = 3CH 2 (OH)-CH 2 (OH) +2MnO 2 + 2KOH

During the severe oxidation of alkenes with a boiling solution of potassium permanganate in an acidic environment, complete cleavage of the bond (σ-bond) occurs with the formation of ketones, carboxylic acids or carbon dioxide:

Oxidation of ethylene with oxygen at 200C in the presence of CuCl 2 and PdCl 2 leads to the formation of acetaldehyde:

CH 2 = CH 2 +1/2O 2 = CH 3 -CH = O

Alkenes undergo polymerization reactions. Polymerization is the process of forming a high-molecular compound - a polymer - by combining with each other using the main valences of the molecules of the original low-molecular substance - the monomer. Polymerization can be caused by heat, ultra-high pressure, irradiation, free radicals or catalysts. Thus, the polymerization of ethylene occurs under the action of acids (cat ion mechanism) or radicals (radical mechanism):

n CH 2 = CH 2 = -(-CH 2 -CH 2 -) n —

Physical properties of alkenes

Under normal conditions, C 2 -C 4 are gases, C 5 -C 17 are liquids, and starting from C 18 are solids. Alkenes are insoluble in water but highly soluble in organic solvents.

Preparation of alkenes

The main methods for obtaining alkenes:

— dehydrohalogenation of halogenated alkanes under the influence of alcoholic solutions of alkalis

CH 3 -CH 2 -CHBr-CH 3 + KOH = CH 3 -CH = CH-CH 3 + KBr + H 2 O

— dehalogenation of dihalogen derivatives of alkanes under the influence of active metals

CH 3 -CHCl-CHCl-CH 3 + Zn = ZnCl 2 + CH 3 -CH = CH-CH 3

— dehydration of alcohols when heated with sulfuric acid (t >150 C) or passing alcohol vapor over a catalyst

CH 3 -CH(OH)- CH 3 = CH 3 -CH = CH 2 + H 2 O

— dehydrogenation of alkanes by heating (500C) in the presence of a catalyst (Ni, Pt, Pd)

CH 3 -CH 2 - CH 3 = CH 3 -CH = CH 2 + H 2

Alkenes are used as starting products in the production of polymeric materials (plastics, rubbers, films) and other organic substances.

Examples of problem solving

EXAMPLE 1

Exercise	Install molecular formula an alkene, if it is known that the same amount of it, interacting with halogens, forms, respectively, either 56.5 g of a dichloro derivative or 101 g of a dibromo derivative.
Solution	The chemical properties of alkenes are determined by their ability to add substances through the mechanism of electrophilic addition, in which the double bond is converted into a single bond: CnH 2 n + Cl 2 → CnH 2 nCl 2 CnH 2 n + Br 2 → CnH 2 nBr 2 The mass of the alkene that entered into the reaction is the same, which means that the same number of moles of alkene participates in the reaction. Let us express the number of moles of hydrocarbon if molar mass dichloro derivative 12n+2n+71, molar mass of dibromo derivative (12n+2n+160): m(CnH 2 nCl 2) \ (12n+2n+71) = m(СnH 2 nBr 2) \ (12n+2n+160) 56.5 \ (12n+2n+71) = 101 \ (12n+2n+160) Therefore, the alkene has the formula C 3 H 6 is propene.
Answer	Alkene formula C 3 H 6 is propene

EXAMPLE 2

Exercise

Carry out a series of transformations ethane → ethene → ethanol → ethene → chloroethane → butane

Solution

To obtain ethene from ethane, it is necessary to use the ethane dehydrogenation reaction, which occurs in the presence of a catalyst (Ni, Pd, Pt) and upon heating: C 2 H 6 →C 2 H 4 + H 2 Ethanol is produced from ethene by a hydration reaction with water in the presence of mineral acids (sulfuric, phosphoric): C 2 H 4 + H 2 O = C 2 H 5 OH To obtain ethene from ethanol, a dehydration reaction is used: C 2 H 5 OH → (t, H 2 SO 4) → C 2 H 4 + H 2 O The production of chloroethane from ethene is carried out by the hydrohalogenation reaction: C 2 H 4 + HCl → C 2 H 5 Cl To obtain butane from chloroethane, the Wurtz reaction is used: 2C 2 H 5 Cl + 2Na → C 4 H 10 + 2NaCl

The physical properties of alkenes are similar to those of alkanes, although they all have slightly lower melting and boiling points than the corresponding alkanes. For example, pentane has a boiling point of 36 °C, and pentene-1 - 30 °C. Under normal conditions, alkenes C 2 - C 4 are gases. C 5 – C 15 are liquids, starting from C 16 are solids. Alkenes are insoluble in water but highly soluble in organic solvents.

Alkenes are rare in nature. Since alkenes are valuable raw materials for industrial organic synthesis, many methods for their preparation have been developed.

1. The main industrial source of alkenes is the cracking of alkanes that are part of oil:

3. In laboratory conditions, alkenes are obtained by elimination reactions, in which two atoms or two groups of atoms are eliminated from neighboring carbon atoms, and an additional p-bond is formed. Such reactions include the following.

1) Dehydration of alcohols occurs when they are heated with water-removing agents, for example with sulfuric acid at temperatures above 150 ° C:

When H 2 O is eliminated from alcohols, HBr and HCl from alkyl halides, the hydrogen atom is preferentially eliminated from that of the neighboring carbon atoms that is bonded to the smallest number of hydrogen atoms (from the least hydrogenated carbon atom). This pattern is called Zaitsev's rule.

3) Dehalogenation occurs when dihalides that have halogen atoms at adjacent carbon atoms are heated with active metals:

CH 2 Br -CHBr -CH 3 + Mg → CH 2 =CH-CH 3 + Mg Br 2.

The chemical properties of alkenes are determined by the presence of a double bond in their molecules. The electron density of the p-bond is quite mobile and easily reacts with electrophilic particles. Therefore, many reactions of alkenes proceed according to the mechanism electrophilic addition, designated by the symbol A E (from English, addition electrophilic). Electrophilic addition reactions are ionic processes that occur in several stages.

In the first stage, an electrophilic particle (most often this is an H + proton) interacts with the p-electrons of the double bond and forms a p-complex, which is then converted into a carbocation by forming a covalent s-bond between the electrophilic particle and one of the carbon atoms:

alkene p-complex carbocation

In the second stage, the carbocation reacts with the X - anion, forming a second s-bond due to the electron pair of the anion:

In electrophilic addition reactions, a hydrogen ion attaches to the carbon atom at the double bond that has a greater negative charge. The charge distribution is determined by the shift in p-electron density under the influence of substituents: .

Electron-donating substituents exhibiting the +I effect shift the p-electron density to a more hydrogenated carbon atom and create a partial negative charge on it. This explains Markovnikov's rule: when adding polar molecules like HX (X = Hal, OH, CN, etc.) to unsymmetrical alkenes, hydrogen preferentially attaches to the more hydrogenated carbon atom at the double bond.

Let's look at specific examples of addition reactions.

1) Hydrohalogenation. When alkenes interact with hydrogen halides (HCl, HBr), alkyl halides are formed:

CH 3 -CH = CH 2 + HBr ® CH 3 -CHBr-CH 3 .

The reaction products are determined by Markovnikov's rule.

It should, however, be emphasized that in the presence of any organic peroxide, polar HX molecules do not react with alkenes according to Markovnikov’s rule:

	R-O-O-R
CH 3 -CH = CH 2 + HBr		CH 3 -CH 2 -CH 2 Br

This is due to the fact that the presence of peroxide determines the radical rather than ionic mechanism of the reaction.

2) Hydration. When alkenes react with water in the presence of mineral acids (sulfuric, phosphoric), alcohols are formed. Mineral acids act as catalysts and are sources of protons. The addition of water also follows Markovnikov’s rule:

CH 3 -CH = CH 2 + HON ® CH 3 -CH (OH) -CH 3 .

3) Halogenation. Alkenes discolor bromine water:

CH 2 = CH 2 + Br 2 ® B-CH 2 -CH 2 Br.

This reaction is qualitative for a double bond.

4) Hydrogenation. The addition of hydrogen occurs under the action of metal catalysts:

where R = H, CH 3, Cl, C 6 H 5, etc. The CH 2 =CHR molecule is called a monomer, the resulting compound is called a polymer, the number n is the degree of polymerization.

Polymerization of various alkene derivatives produces valuable industrial products: polyethylene, polypropylene, polyvinyl chloride and others.

In addition to addition, alkenes also undergo oxidation reactions. During the mild oxidation of alkenes with an aqueous solution of potassium permanganate (Wagner reaction), dihydric alcohols are formed:

ZSN 2 =CH 2 + 2KMn O 4 + 4H 2 O ® ZNOSN 2 -CH 2 OH + 2MnO 2 ↓ + 2KOH.

As a result of this reaction, the purple solution of potassium permanganate quickly becomes discolored and a brown precipitate of manganese (IV) oxide precipitates. This reaction, like the decolorization reaction of bromine water, is qualitative for a double bond. During the severe oxidation of alkenes with a boiling solution of potassium permanganate in an acidic environment, the double bond is completely broken with the formation of ketones, carboxylic acids or CO 2, for example:

	[ABOUT]
CH 3 -CH=CH-CH 3		2CH 3 -COOH

Based on the oxidation products, the position of the double bond in the original alkene can be determined.

Like all other hydrocarbons, alkenes burn and, with plenty of air, form carbon dioxide and water:

C n H 2 n + Zn /2O 2 ® n CO 2 + n H 2 O.

When air is limited, combustion of alkenes can lead to the formation of carbon monoxide and water:

C n H 2n + nO 2 ® nCO + nH 2 O .

If you mix an alkene with oxygen and pass this mixture over a silver catalyst heated to 200°C, an alkene oxide (epoxyalkane) is formed, for example:

At any temperature, alkenes are oxidized by ozone (ozone is a stronger oxidizing agent than oxygen). If ozone gas is passed through a solution of an alkene in methane tetrachloride at temperatures below room temperature, an addition reaction occurs and the corresponding ozonides (cyclic peroxides) are formed. Ozonides are very unstable and can explode easily. Therefore, they are usually not isolated, but immediately after production they are decomposed with water - this produces carbonyl compounds (aldehydes or ketones), the structure of which indicates the structure of the alkene that was subjected to ozonation.

Lower alkenes are important starting materials for industrial organic synthesis. From ethylene it is obtained ethanol, polyethylene, polystyrene. Propene is used for the synthesis of polypropylene, phenol, acetone, and glycerin.

Unsaturated include hydrocarbons containing multiple bonds between carbon atoms in their molecules. Unlimited are alkenes, alkynes, alkadienes (polyenes). Cyclic hydrocarbons containing a double bond in the ring ( cycloalkenes), as well as cycloalkanes with a small number of carbon atoms in the ring (three or four atoms). 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.

Structure of alkenes

Acyclic hydrocarbons containing in the molecule, in addition to single bonds, one double bond between carbon atoms and corresponding to the general formula CnH2n. Its second name is olefins- alkenes were obtained by analogy with unsaturated fatty acids (oleic, linoleic), the remains of which are part of liquid fats - oils.
Carbon atoms between which there is a double bond are in a state of sp 2 hybridization. This means that one s and two p orbitals are involved in hybridization, and one p orbital remains unhybridized. The overlap of hybrid orbitals leads to the formation of a σ bond, and due to unhybridized p orbitals
neighboring carbon atoms, a second, π-bond is formed. Thus, a double bond consists of one σ- and one π-bond. The hybrid orbitals of the atoms forming a double bond are in the same plane, and the orbitals forming a π bond are located perpendicular to the plane of the molecule. A double bond (0.132 im) is shorter than a single bond, and its energy is greater, because it is stronger. However, the presence of a mobile, easily polarized π bond leads to the fact that alkenes are chemically more active than alkanes and are able to undergo addition reactions.

Structure of ethylene

Double bond formation in alkenes

Homologous series of ethene

Straight alkenes form the homologous series of ethene ( ethylene): C 2 H 4 - ethene, C 3 H 6 - propene, C 4 H 8 - butene, C 5 H 10 - pentene, C 6 H 12 - hexene, C 7 H 14 - heptene, etc.

Alkene isomerism

Alkenes are characterized by structural isomerism. 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 isomerism of the position of the double bond:

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

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 and transisomerism.

Cis isomers different from trans isomers the spatial arrangement of molecular fragments (in this case, methyl groups) relative to the π-bond plane, and, consequently, properties.

Alkene nomenclature

1. Selection 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. In the case of alkenes, the main chain must contain a double bond.
2. Numbering of atoms of the main chain. The numbering of the atoms of the main chain begins from the end to which the double bond is closest.
For example, the correct connection name is:

If the position of the double bond cannot determine the beginning of the numbering of atoms in the chain, then it is determined by the position of the substituents in the same way as for saturated hydrocarbons.

3. Formation of the name. At the end of the name indicate the number of the carbon atom at which the double bond begins, and the suffix -en, indicating that the compound belongs to the class of alkenes. For example:

Physical properties of alkenes

The first three representatives of the homologous series of alkenes are gases; substances of the composition C5H10 - C16H32 - liquids; Higher alkenes are solids.
The boiling and melting points naturally increase with increasing molecular weight connections.

Chemical properties of alkenes

Addition reactions. Let us remind you that distinctive feature representatives of unsaturated hydrocarbons - alkenes is the ability to enter into addition reactions. Most of these reactions proceed according to the mechanism electrophilic addition.
1. Hydrogenation of alkenes. Alkenes are capable of adding hydrogen in the presence of hydrogenation catalysts, metals - platinum, palladium, nickel:

This reaction occurs at atmospheric and elevated pressure and does not require high temperature, because it is exothermic. When the temperature increases, the same catalysts can cause a reverse reaction - dehydrogenation.

2. Halogenation (addition of halogens). The interaction of an alkene with bromine water or a solution of bromine in an organic solvent (CC14) leads to rapid discoloration of these solutions as a result of the addition of a halogen molecule to the alkene and the formation of dihaloalkanes.
3. Hydrohalogenation (addition of hydrogen halide).

This reaction obeys
When a hydrogen halide attaches to an alkene, the hydrogen attaches to the more hydrogenated carbon atom, i.e., the atom at which there are more hydrogen atoms, and the halogen to the less hydrogenated one.

4. Hydration (addition of water). Hydration of alkenes leads to the formation of alcohols. For example, the addition of water to ethene is the basis of one of the industrial methods for producing ethyl alcohol.

Please note that primary alcohol(with a hydroxo group at the primary carbon) is formed only upon hydration of ethene. When propene or other alkenes are hydrated, they form secondary alcohols.

This reaction also proceeds in accordance with Markovnikov's rule - a hydrogen cation attaches to a more hydrogenated carbon atom, and a hydroxo group to a less hydrogenated one.
5. Polymerization. A special case of addition is the polymerization reaction of alkenes:

This addition reaction occurs via a free radical mechanism.
Oxidation reactions.
1. Combustion. Like any organic compounds, alkenes burn in oxygen to form CO2 and H2O:

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