The occurrence of alkenes in nature is brief. Physical properties of alkenes, applications, methods of preparation

Alkene hydrocarbons (olefins) are one of the classes of organic substances that have their own properties. The types of isomerism of alkenes in representatives of this class are not repeated with the isomerism of other organic substances.

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Characteristics of the class

Ethylene olefins are called one of the classes of unsaturated hydrocarbons containing one double bond.

According to physical properties, representatives of this category of unsaturated compounds are:

• gases,
• liquids,
• solid compounds.

The molecules contain not only a “sigma” bond, but also a “pi” bond. The reason for this is the presence in the structural formula of hybridization “ sp2", which is characterized by the arrangement of the atoms of the compound in the same plane.

In this case, an angle of at least one hundred and twenty degrees is formed between them. Unhybridized orbitals " R» is characterized by its location both on top of the molecular plane and below it.

This structural feature leads to the formation of additional bonds - “pi” or “ π ».

The described bond is less strong compared to “sigma” bonds, since overlapping sideways has weak adhesion. The total distribution of electron densities of formed bonds is characterized by heterogeneity. When rotating near a carbon-carbon bond, the overlap of the “p” orbitals is disrupted. For each alkene (olefin), this pattern is a distinctive feature.

Almost all ethylene compounds have high boiling and melting points, which are not characteristic of all organic substances. Representatives of this class of unsaturated carbohydrates quickly dissolve in other organic solvents.

Attention! Acyclic unsaturated compounds, ethylene hydrocarbons, have the general formula - C n H 2n.

Homology

Based on the fact that the general formula of alkenes is C n H 2n, they have a certain homology. The homologous series of alkenes begins with the first representative, ethylene or ethene. This substance under normal conditions is a gas and contains two carbon atoms and four hydrogen atoms -C2H4. After ethene, the homologous series of alkenes continues with propene and butene. Their formulas are as follows: “C 3 H 6” and “C 4 H 8”. Under normal conditions, they are also gases that are heavier, which means they must be collected with a test tube turned upside down.

The general formula of alkenes allows us to calculate the next representative of this class, which has at least five carbon atoms in the structural chain. This is a pentene with the formula "C 5 H 10".

By physical characteristics the indicated substance belongs to liquids, as well as the following twelve compounds of the homologous line.

Among alkenes with these characteristics, there are also solids that begin with the formula C 18 H 36. Liquid and solid ethylene hydrocarbons do not dissolve in water, but when they enter organic solvents they react with them.

The described general formula of alkenes implies the replacement of the previously used suffix “an” with “en”. This is enshrined in IUPAC rules. Whatever representative of this category of compounds we take, they all have the described suffix.

The names of ethylene compounds always contain a certain number, which indicates the location of the double bond in the formula. Examples of this are: “butene-1” or “pentene-2”. Atomic numbering begins from the edge to which the double configuration is closest. This rule is “iron” in all cases.

Isomerism

Depending on the type of hybridization of alkenes, they are characterized by certain types of isomerism, each of which has its own characteristics and structure. Let us consider the main types of isomerism of alkenes.

Structural type

Structural isomerism is divided into isomers according to:

• carbon skeleton;
• location of the double bond.

Structural isomers of the carbon skeleton arise when radicals (branches from the main chain) appear.

Isomers of alkenes of the indicated isomerism will be:

CH 2 =CH — CH 2 — CH 3.

2-methylpropene-1:

CH 2 =C — CH 3

│

The presented compounds have a common number of carbon and hydrogen atoms (C 4 H 8), but a different structure of the hydrocarbon skeleton. These are structural isomers, although their properties are not the same. Butene-1 (butylene) has a characteristic odor and narcotic properties that irritate the respiratory tract. 2-methylpropen-1 does not have these features.

IN in this case There are no isomers in ethylene (C 2 H 4), since it consists of only two carbon atoms, where radicals cannot be substituted.

Advice! The radical is allowed to be placed on the middle and penultimate carbon atoms, but it is not allowed to place them near the extreme substituents. This rule works for all unsaturated hydrocarbons.

Based on the location of the double bond, isomers are distinguished:

CH 2 =CH — CH 2 — CH 2 -CH 3.

CH 3 -CH = CH — CH 2 -CH 3.

The general formula of alkenes in the examples presented is:C 5 H 10,, but the location of one double bond is different. The properties of these compounds will vary. This is structural isomerism.

Isomerism

Spatial type

The spatial isomerism of alkenes is associated with the nature of the arrangement of hydrocarbon substituents.

Based on this, isomers are distinguished:

• "Cis";
• "Trance".

The general formula of alkenes allows for the creation of “trans isomers” and “cis isomers” of the same compound. Take butylene (butene), for example. For it, it is possible to create isomers with a spatial structure by differently positioning the substituents relative to the double bond. With examples, isomerism of alkenes will look like this:

"cis-isomer" "trans-isomer"

Butene-2 ​​Butene-2

From the above example It can be seen that “cis-isomers” have two identical radicals on one side of the double bond plane. For “trans-isomers” this rule does not work, since they have two dissimilar substituents located relative to the “C=C” carbon chain. Considering this pattern, you can construct “cis” and “trans” isomers yourself for various acyclic ethylene hydrocarbons.

The presented “cis isomer” and “trans isomer” for butene-2 ​​cannot be converted into one another, since this requires rotation around the existing carbon double chain (C=C). To carry out this rotation, a certain amount of energy is required to break the existing “p-bond”.

Based on all of the above, we can conclude that “trans” and “cis” isomers are individual compounds with a specific set of chemical and physical properties.

Which alkene has no isomers? Ethylene has no spatial isomers due to the identical arrangement of hydrogen substituents relative to the double chain.

Interclass

Interclass isomerism in alkene hydrocarbons is widespread. The reason for this is the similarity general formula representatives of this class with the formula cycloparaffins (cycloalkanes). These categories of substances have the same number of carbon and hydrogen atoms, a multiple of the composition (C n H 2n).

Interclass isomers will look like this:

CH 2 =CH — CH 3.

Cyclopropane:

It turns out that the formulaC3H6Two compounds answer: propene-1 and cyclopropane. The structural structure shows the different arrangement of carbon relative to each other. The properties of these compounds are also different. Propene-1 (propylene) is a gaseous compound with a low boiling point. It is typical for cyclopropane gaseous state with a pungent odor and acrid taste. Chemical properties These substances also differ, but their composition is identical. In organic this type of isomers is called interclass.

Alkenes. Isomerism of alkenes. Unified State Exam. Organic chemistry.

Alkenes: Structure, nomenclature, isomerism

Conclusion

Alkene isomerism is their important characteristic, thanks to which new compounds with different properties appear in nature, which find application in industry and everyday life.

UNSATURATED OR UNSATURATED HYDROCARBONS OF THE ETHYLENE SERIES

(ALKENES OR OLEFINS)

Alkenes, or olefins(from Latin olefiant - oil - an old name, but widely used in chemical literature. The reason for this name was ethylene chloride, obtained in the 18th century, is a liquid, oily substance.) - aliphatic unsaturated hydrocarbons, in the molecules of which there is one double bond between the carbon atoms.

Alkenes contain fewer hydrogen atoms in their molecule than their corresponding alkanes (with the same number of carbon atoms), therefore such hydrocarbons are called unlimited or unsaturated.

Alkenes form a homologous series with the general formula CnH2n

1. Homologous series of alkenes

WITH n H 2 n alkene	Names, suffix EH, ILENE
C2H4	this en, this Ilen
C3H6	propene
C4H8	butene
C5H10	penten
C6H12	hexene

Homologues:

WITHH 2 = CH 2 ethene

WITHH 2 = CH- CH 3 propene

WITHH 2 =CH-CH 2 -CH 3butene-1

WITHH 2 =CH-CH 2 -CH 2 -CH 3 penten-1

2. Physical properties

Ethylene (ethene) is a colorless gas with a very weak sweetish odor, slightly lighter than air, slightly soluble in water.

C 2 – C 4 (gases)

C 5 – C 17 (liquids)

C 18 – (solid)

· Alkenes are insoluble in water, soluble in organic solvents (gasoline, benzene, etc.)

Lighter than water

With increasing Mr, the melting and boiling points increase

3. The simplest alkene is ethylene - C2H4

The structural and electronic formulas of ethylene are:

In the ethylene molecule one undergoes hybridization s- and two p-orbitals of C atoms ( sp 2 -hybridization).

Thus, each C atom has three hybrid orbitals and one non-hybrid p-orbitals. Two of the hybrid orbitals of the C atoms mutually overlap and form between the C atoms

σ - bond. The remaining four hybrid orbitals of the C atoms overlap in the same plane with four s-orbitals of H atoms and also form four σ - bonds. Two non-hybrid p-orbitals of C atoms mutually overlap in a plane that is located perpendicular to the σ-bond plane, i.e. one is formed P- connection.

By it's nature P- connection is sharply different from σ - connection; P- the bond is less strong due to the overlap of electron clouds outside the plane of the molecule. Under the influence of reagents P- the connection is easily broken.

The ethylene molecule is symmetrical; the nuclei of all atoms are located in the same plane and bond angles are close to 120°; the distance between the centers of C atoms is 0.134 nm.

If atoms are connected by a double bond, then their rotation is impossible without electron clouds P- the connection was not opened.

4. Isomerism of alkenes

Along with structural isomerism of the carbon skeleton Alkenes are characterized, firstly, by other types of structural isomerism - multiple bond position isomerism And interclass isomerism.

Secondly, in the series of alkenes there is spatial isomerism , associated with different positions of substituents relative to the double bond, around which intramolecular rotation is impossible.

Structural isomerism of alkenes

1. Isomerism of the carbon skeleton (starting from C 4 H 8):

2. Isomerism of the position of the double bond (starting from C 4 H 8):

3. Interclass isomerism with cycloalkanes, starting with C 3 H 6:

Spatial isomerism of alkenes

Rotation of atoms around a double bond is impossible without breaking it. This is due to the structural features of the p-bond (the p-electron cloud is concentrated above and below the plane of the molecule). Due to the rigid fixation of the atoms, rotational isomerism with respect to the double bond does not appear. But it becomes possible cis-trance-isomerism.

Alkenes, which have different substituents on each of the two carbon atoms at the double bond, can exist in the form of two spatial isomers, differing in the location of the substituents relative to the plane of the p-bond. So, in the butene-2 ​​molecule CH 3 –CH=CH–CH 3 CH 3 groups can be located either on one side of the double bond in cis-isomer, or on opposite sides in trance-isomer.

ATTENTION! cis-trans- Isomerism does not appear if at least one of the C atoms at the double bond has 2 identical substituents.

For example,

butene-1 CH 2 = CH – CH 2 – CH 3 doesn't have cis- And trance-isomers, because The 1st C atom is bonded to two identical H atoms.

Isomers cis- And trance- differ not only physically

,

but also chemical properties, because bringing parts of a molecule closer or further away from each other in space promotes or hinders chemical interaction.

Sometimes cis-trans-isomerism is not quite accurately called geometric isomerism. The inaccuracy is that All spatial isomers differ in their geometry, and not only cis- And trance-.

5. Nomenclature

Alkenes of simple structure are often named by replacing the suffix -ane in alkanes with -ylene: ethane - ethylene, propane - propylene, etc.

According to systematic nomenclature, the names of ethylene hydrocarbons are made by replacing the suffix -ane in the corresponding alkanes with the suffix -ene (alkane - alkene, ethane - ethene, propane - propene, etc.). The choice of the main chain and the naming order are the same as for alkanes. However, the chain must necessarily include a double bond. The numbering of the chain begins from the end to which this connection is located closest. For example:

Unsaturated (alkene) radicals are called by trivial names or by systematic nomenclature:

(H 2 C=CH-)vinyl or ethenyl

(H 2 C=CH-CH 2) allyl

Lesson topic: Alkenes. Preparation, chemical properties and applications of alkenes.

Goals and objectives of the lesson:

• consider the specific chemical properties of ethylene and general properties alkenes;
• deepen and concretize the concepts of?-connection, mechanisms chemical reactions;
• give initial ideas about polymerization reactions and the structure of polymers;
• analyze laboratory and general industrial methods for producing alkenes;
• continue to develop the ability to work with the textbook.

Equipment: device for producing gases, KMnO 4 solution, ethyl alcohol, concentrated sulfuric acid, matches, alcohol lamp, sand, tables “Structure of the ethylene molecule”, “Basic chemical properties of alkenes”, demonstration samples “Polymers”.

DURING THE CLASSES

I. Organizational moment

We continue to study the homologous series of alkenes. Today we have to look at the methods of preparation, chemical properties and applications of alkenes. We must characterize the chemical properties caused by the double bond, gain an initial understanding of polymerization reactions, and consider laboratory and industrial methods for producing alkenes.

II. Activating students' knowledge

1. What hydrocarbons are called alkenes?

1. What are the features of their structure?

1. In what hybrid state are the carbon atoms that form a double bond in an alkene molecule?

Bottom line: alkenes differ from alkanes in the presence of one double bond in their molecules, which determines the peculiarities of the chemical properties of alkenes, methods of their preparation and use.

III. Learning new material

1. Methods for producing alkenes

Draw up reaction equations confirming methods for producing alkenes

– cracking of alkanes C 8 H 18 ––> C 4 H 8 + C 4 H 10 ; (thermal cracking at 400-700 o C)
octane butene butane
– dehydrogenation of alkanes C 4 H 10 ––> C 4 H 8 + H 2; (t, Ni)
butane butene hydrogen
– dehydrohalogenation of haloalkanes C 4 H 9 Cl + KOH ––> C 4 H 8 + KCl + H 2 O;
chlorobutane hydroxide butene chloride water
potassium potassium
– dehydrohalogenation of dihaloalkanes
– dehydration of alcohols C 2 H 5 OH ––> C 2 H 4 + H 2 O (when heated in the presence of concentrated sulfuric acid)
Remember! In the reactions of dehydrogenation, dehydration, dehydrohalogenation and dehalogenation, it must be remembered that hydrogen is preferentially abstracted from less hydrogenated carbon atoms (Zaitsev’s rule, 1875)

2. Chemical properties of alkenes

The nature of the carbon-carbon bond determines the type of chemical reactions in which organic matter. The presence of a double carbon-carbon bond in the molecules of ethylene hydrocarbons determines the following features of these compounds:
– the presence of a double bond allows alkenes to be classified as unsaturated compounds. Their transformation into saturated ones is possible only as a result of addition reactions, which is the main feature of the chemical behavior of olefins;
– the double bond represents a significant concentration of electron density, so addition reactions are electrophilic in nature;
– a double bond consists of one - and one - bond, which is quite easily polarized.

Reaction equations characterizing the chemical properties of alkenes

a) Addition reactions

Remember! Substitution reactions are characteristic of alkanes and higher cycloalkanes, which have only single bonds; addition reactions are characteristic of alkenes, dienes and alkynes, which have double and triple bonds.

Remember! The following mechanisms for breaking the -bond are possible:

a) if alkenes and the reagent are non-polar compounds, then the -bond is broken to form a free radical:

H 2 C = CH 2 + H: H ––> + +

b) if the alkene and the reagent are polar compounds, then the cleavage of the -bond leads to the formation of ions:

c) when reagents containing hydrogen atoms in the molecule join at the site of a broken -bond, hydrogen always attaches to a more hydrogenated carbon atom (Morkovnikov’s rule, 1869).

– polymerization reaction nCH 2 = CH 2 ––> n – CH 2 – CH 2 –– > (– CH 2 – CH 2 –)n
ethene polyethylene

b) oxidation reaction

Laboratory experience. Obtain ethylene and study its properties (instructions on student desks)

Instructions for obtaining ethylene and experiments with it

1. Place 2 ml of concentrated sulfuric acid, 1 ml of alcohol and a small amount of sand into a test tube.
2. Close the test tube with a stopper with a gas outlet tube and heat it in the flame of an alcohol lamp.
3. Pass the released gas through a solution with potassium permanganate. Note the change in color of the solution.
4. Light the gas at the end of the gas outlet tube. Pay attention to the color of the flame.

– alkenes burn with a luminous flame. (Why?)

C 2 H 4 + 3O 2 ––> 2CO 2 + 2H 2 O (with complete oxidation, the reaction products are carbon dioxide and water)

Qualitative reaction: “mild oxidation (in aqueous solution)”

– alkenes decolorize a solution of potassium permanganate (Wagner reaction)

Under more severe conditions in an acidic environment, the reaction products can be carboxylic acids, for example (in the presence of acids):

CH 3 – CH = CH 2 + 4 [O] ––> CH 3 COOH + HCOOH

– catalytic oxidation

Remember the main thing!

1. Unsaturated hydrocarbons actively participate in addition reactions.
2. The reactivity of alkenes is due to the fact that the bond is easily broken under the influence of reagents.
3. As a result of addition, the transition of carbon atoms from sp 2 to sp 3 - a hybrid state occurs. The reaction product has a limiting character.
4. When ethylene, propylene and other alkenes are heated under pressure or in the presence of a catalyst, their individual molecules are combined into long chains - polymers. Polymers (polyethylene, polypropylene) are of great practical importance.

3. Application of alkenes(student message according to the following plan).

1 – production of fuel with a high octane number;
2 – plastics;
3 – explosives;
4 – antifreeze;
5 – solvents;
6 – to accelerate fruit ripening;
7 – production of acetaldehyde;
8 – synthetic rubber.

III. Reinforcing the material learned

Homework:§§ 15, 16, ex. 1, 2, 3 p. 90, ex. 4, 5 p. 95.

Lower alkenes (C 2 - C 5) are produced on an industrial scale from gases formed during the thermal processing of oil and petroleum products. Alkenes can also be prepared using laboratory synthesis methods.

4.5.1. Dehydrohalogenation

When haloalkanes are treated with bases in anhydrous solvents, for example, an alcoholic solution of potassium hydroxide, hydrogen halide is eliminated.

4.5.2. Dehydration

When alcohols are heated with sulfuric or phosphoric acids, intramolecular dehydration occurs (  - elimination).

The predominant direction of the reaction, as in the case of dehydrohalogenation, is the formation of the most stable alkene (Zaitsev’s rule).

Dehydration of alcohols can be carried out by passing alcohol vapor over a catalyst (aluminum or thorium oxides) at 300 - 350 o C.

4.5.3. Dehalogenation of vicinal dihalides

By the action of zinc in alcohol, dibromides containing halogens at neighboring atoms (vicinal) can be converted into alkenes.

4.5.4. Hydrogenation of alkynes

When alkynes are hydrogenated in the presence of platinum or nickel catalysts, the activity of which is reduced by the addition of a small amount of lead compounds (catalytic poison), an alkene is formed that does not undergo further reduction.

4.5.5. Reductive combination of aldehydes and ketones

When treated with lithium aluminum hydride and titanium(III) chloride from two molecules of aldehyde or ketone with good exits Di- or tetra-substituted alkenes are formed, respectively.

5. ALKYNE

Alkynes are hydrocarbons containing a triple carbon-carbon bond –СС–.

The general formula of simple alkynes is C n H 2n-2. The simplest representative of the class of alkynes is acetylene H–СС–H, therefore alkynes are also called acetylene hydrocarbons.

5.1. The structure of acetylene

The carbon atoms of acetylene are in sp- hybrid state. Let us depict the orbital configuration of such an atom. During hybridization 2s-orbitals and 2p-orbitals are formed into two equal ones sp-hybrid orbitals located on the same straight line, leaving two unhybridized ones R-orbitals.

Rice. 5.1 Schemeformationsp -hybrid orbitals of the carbon atom

Directions and shapes of orbitals sR-hybridized carbon atom: hybridized orbitals are equivalent, maximally distant from each other

In the acetylene molecule there is a single bond (  - bond) between carbon atoms is formed by the overlap of two sp-hybridized orbitals. Two mutually perpendicular  - bonds arise when two pairs of unhybridized pairs overlap laterally 2p- orbitals,  - electron clouds cover the skeleton so that the electron cloud has symmetry close to cylindrical. Bonds with hydrogen atoms are formed due to sp-hybrid orbitals of the carbon atom and 1 s-orbitals of the hydrogen atom, the acetylene molecule is linear.

Rice. 5.2 Acetylene molecule

a - lateral overlap 2p gives two orbitals  - communications;

b - the molecule is linear,  -the cloud has a cylindrical shape

In propyne there is a simple connection (  - communication with sp-WITH sp3 shorter than a similar connection C sp-WITH sp2 in alkenes, this is explained by the fact that sp- the orbital is closer to the nucleus than sp 2 - orbital .

The carbon-carbon triple bond C  C is shorter than the double bond, and the total energy of the triple bond is approximately equal to the sum of the energies of one single C–C bond (347 kJ/mol) and two  bonds (259 2 kJ/mol) (Table 5.1 ).

Alkenes are characterized primarily by reactions accession through a double bond. Basically, these reactions proceed by an ionic mechanism. The pi bond is broken and two new sigma bonds are formed. Let me remind you that substitution reactions were typical for alkanes and they followed a radical mechanism. Hydrogen molecules can attach to alkenes; these reactions are called hydrogenation, water molecules, hydration, halogens halogenation, hydrogen halides hydrohalogenation. But first things first.

Double bond addition reactions

So, first chemical property ability to add hydrogen halides, hydrohalogenation.

Propene and other alkenes react with hydrogen halides according to Markovnikov's rule.

A hydrogen atom attaches to the most hydrogenated, or more correctly hydrogenated, carbon atom.

Second number on our list of properties would be hydration, the addition of water.

The reaction takes place when heated in the presence of an acid, usually sulfuric or phosphoric. The addition of water also occurs according to Markovnikov’s rule, that is, primary alcohol can only be obtained by hydration of ethylene, the remaining unbranched alkenes give secondary alcohols.

There are exceptions to Markovnikov's rule for both hydrohalogenation and hydration. Firstly, contrary to this rule, the addition occurs in the presence of peroxides.

Secondly, for derivatives of alkenes in which electron-withdrawing groups are present. For example, for 3,3,3-trifluoropropene-1.

Fluorine atoms, due to their high electronegativity, attract electron density to themselves along a chain of sigma bonds. This phenomenon is called a negative inductive effect.

Because of this, the mobile pi electrons of the double bond are displaced and the outermost carbon atom ends up with a partial positive charge, which is usually designated as delta plus. It is to this that the negatively charged bromine ion will go, and the hydrogen cation will attach to the least hydrogenated carbon atom.

In addition to the trifluoromethyl group, for example, the trichloromethyl group, nitro group, carboxyl group and some others have a negative inductive effect.

This second case of violation of the Markovnikov rule in the Unified State Exam is very rare, but it is still advisable to keep it in mind if you plan to pass the exam with the maximum score.

Third chemical property attachment of halogen molecules.

This primarily concerns bromine, since this reaction is qualitative for a multiple bond. When passing, for example, ethylene through bromine water, that is, a solution of bromine in water having Brown color, it becomes discolored. If you pass a mixture of gases, for example, ethane and ethene, through bromine water, you can get pure ethane without ethene impurities, since it will remain in the reaction flask in the form of dibromoethane, which is a liquid.

Of particular note is the reaction of alkenes in the gas phase with strong heating, for example, with chlorine.

Under such conditions, it is not an addition reaction that occurs, but a substitution reaction. Moreover, exclusively at the alpha carbon atom, that is, the atom adjacent to the double bond. In this case, 3-chloropropene-1 is obtained. These reactions are infrequent in the exam, so most students do not remember them and, as a rule, make mistakes.

Fourth number is the hydrogenation reaction, and with it the dehydrogenation reaction. That is, the addition or removal of hydrogen.

Hydrogenation occurs at not very high temperature on a nickel catalyst. At higher temperatures, dehydrogenation is possible to produce alkynes.

Fifth A property of alkenes is the ability to polymerize, when hundreds and thousands of alkene molecules form very long and strong chains due to the breaking of the pi bond and the formation of sigma bonds with each other.

In this case, the result was polyethylene. Please note that the resulting molecule contains no multiple bonds. Such substances are called polymers, the original molecules are called monomers, the repeating fragment is the elementary unit of the polymer, and the number n is the degree of polymerization.

Reactions producing other important polymer materials, for example, polypropylene.

Another important polymer is polyvinyl chloride.

The starting material for the production of this polymer is chloroethene, whose common name is vinyl chloride. Because this unsaturated substituent is called vinyl. The frequently encountered abbreviation on plastic products, PVC, stands for polyvinyl chloride.

We discussed five properties that represented double bond addition reactions. Now let's look at the reactions oxidation.

Alkene oxidation reactions

Sixth chemical property in our general list This is a mild oxidation or Wagner reaction. It occurs when exposed to an alkene aqueous solution potassium permanganate in the cold, so the temperature of zero degrees is often indicated in exam tasks.

The result is a dihydric alcohol. In this case, ethylene glycol, but in general such alcohols are common name glycols During the reaction, the purple-pink permanganate solution becomes discolored, so this reaction is also qualitative for a double bond. Manganese in a neutral environment is reduced from oxidation state +7 to oxidation state +4. Let's look at a few more examples. THE EQUATION

Here we get propanediol-1,2. However, cyclic alkenes will react in the same way. THE EQUATION

Another option is when the double bond is located, for example, in the side chain of aromatic hydrocarbons. Regularly in exam assignments There is a Wagner reaction involving styrene, its second name is vinylbenzene.

I hope that I have provided enough examples for you to understand that the mild oxidation of a double bond always obeys quite simple rule The pi bond is broken and a hydroxy group is added to each carbon atom.

Now, regarding hard oxidation. It will be ours seventh property. This oxidation occurs when an alkene reacts with an acidic solution of potassium permanganate when heated.

The destruction of the molecule occurs, that is, its destruction at the double bond. In the case of butene-2, two molecules of acetic acid were obtained. In general, the position of the multiple bond in the carbon chain can be judged from the oxidation products.

The oxidation of butene-1 produces a molecule of propionic (propanoic) acid and carbon dioxide.

In the case of ethylene, you get two molecules of carbon dioxide. In all cases, in an acidic environment, manganese is reduced from oxidation state +7 to +2.

And finally eighth property complete oxidation or burning.

Alkenes burn, like other hydrocarbons, to carbon dioxide and water. Let us write the equation for the combustion of alkenes in general form.

There will be as many carbon dioxide molecules as there are carbon atoms in the alkene molecule, since the CO 2 molecule contains one carbon atom. That is, n CO 2 molecules. There will be two times fewer water molecules than hydrogen atoms, that is, 2n/2, which means just n.

There are the same number of oxygen atoms on the left and right. On the right there are 2n of carbon dioxide plus n of water, for a total of 3n. On the left there are the same number of oxygen atoms, which means there are two times fewer molecules, because the molecule contains two atoms. That is, 3n/2 oxygen molecules. You can write 1.5n.

We have reviewed eight chemical properties of alkenes.