Alkenes react with. Unsaturated hydrocarbons

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

Goals and objectives of the lesson:

• review the specific chemical properties of ethylene and the general properties of alkenes;
• deepen and concretize the concepts of?-bonds and the mechanisms of 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”.

PROGRESS OF THE LESSON

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 substances enter. 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.

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:

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 + HOH ® 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:

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. Ethyl alcohol, polyethylene, and polystyrene are produced from ethylene. Propene is used for the synthesis of polypropylene, phenol, acetone, and glycerin.

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.

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".

According to 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 this case, ethylene (C 2 H 4) has no isomers, 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 applies to 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 this example it is clear 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 of the general formula of representatives of this class with the formula of 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. Cyclopropane is characterized by a gaseous state with a pungent odor and pungent taste. The chemical properties of 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 are used in industry and everyday life.

In organic chemistry, you can find hydrocarbon substances with different amounts of carbon in the chain and C=C bond. They are homologues and are called alkenes. Due to their structure, they are chemically more reactive than alkanes. But what kind of reactions are typical for them? Let's consider their distribution in nature, different methods of production and use.

What are they?

Alkenes, also called olefins (oily), get their name from ethene chloride, a derivative of the first member of this group. All alkenes have at least one C=C double bond. C n H 2n is the formula of all olefins, and the name is formed from an alkane with the same number of carbons in the molecule, only the suffix -ane changes to -ene. The Arabic numeral at the end of the name, separated by a hyphen, indicates the number of carbon from which the double bond begins. Let's look at the main alkenes, the table will help you remember them:

If the molecules have a simple, unbranched structure, then the suffix -ylene is added, this is also reflected in the table.

Where can you find them?

Since the reactivity of alkenes is very high, their representatives are extremely rare in nature. The principle of life of an olefin molecule is “let’s be friends.” There are no other substances around - no problem, we will be friends with each other, forming polymers.

But they exist, and a small number of representatives are included in the accompanying petroleum gas, and higher ones are in the oil produced in Canada.

The very first representative of alkenes, ethene, is a hormone that stimulates fruit ripening, so it is synthesized in small quantities by representatives of the flora. There is an alkene, cis-9-tricosene, which plays the role of a sexual attractant in female house flies. It is also called muscalur. (An attractant is a substance of natural or synthetic origin that causes attraction to the source of odor in another organism). From a chemical point of view, this alkene looks like this:

Since all alkenes are very valuable raw materials, the methods for producing them artificially are very diverse. Let's look at the most common ones.

What if you need a lot?

In industry, the class of alkenes is mainly obtained by cracking, i.e. cleavage of the molecule under the influence of high temperatures, higher alkanes. The reaction requires heating in the range of 400 to 700 °C. The alkane splits the way it wants, forming alkenes, the methods of obtaining which we are considering, with a large number of molecular structure options:

C 7 H 16 -> CH 3 -CH=CH 2 + C 4 H 10.

Another common method is called dehydrogenation, in which a hydrogen molecule is separated from a representative of an alkane series in the presence of a catalyst.

In laboratory conditions, alkenes and methods of preparation differ; they are based on elimination reactions (elimination of a group of atoms without their substitution). The most commonly eliminated water atoms from alcohols are halogens, hydrogen or hydrogen halides. The most common way to obtain alkenes is from alcohols in the presence of an acid as a catalyst. It is possible to use other catalysts

All elimination reactions are subject to Zaitsev’s rule, which states:

A hydrogen atom is split off from the carbon adjacent to the carbon bearing the -OH group, which has fewer hydrogens.

Having applied the rule, answer which reaction product will predominate? Later you will find out if you answered correctly.

Chemical properties

Alkenes react actively with substances, breaking their pi bond (another name for the C=C bond). After all, it is not as strong as a single bond (sigma bond). A hydrocarbon is converted from unsaturated to saturated without forming other substances after the reaction (addition).

• addition of hydrogen (hydrogenation). The presence of a catalyst and heating is necessary for its passage;
• addition of halogen molecules (halogenation). It is one of the qualitative reactions to the pi bond. After all, when alkenes react with bromine water, it turns from brown to transparent;
• reaction with hydrogen halides (hydrohalogenation);
• addition of water (hydration). The conditions for the reaction to occur are heating and the presence of a catalyst (acid);

Reactions of unsymmetrical olefins with hydrogen halides and water obey Markovnikov's rule. This means that hydrogen will attach itself to the carbon from the carbon-carbon double bond that already has more hydrogen atoms.

• combustion;
• incomplete oxidation catalytic. The product is cyclic oxides;
• Wagner reaction (oxidation with permanganate in a neutral environment). This alkene reaction is another qualitative C=C bond. As it flows, the pink solution of potassium permanganate becomes discolored. If the same reaction is carried out in a combined acidic environment, the products will be different (carboxylic acids, ketones, carbon dioxide);
• isomerization. All types are characteristic: cis- and trans-, double bond movement, cyclization, skeletal isomerization;
• Polymerization is the main property of olefins for industry.

Application in medicine

The reaction products of alkenes are of great practical importance. Many of them are used in medicine. Glycerin is obtained from propene. This polyhydric alcohol is an excellent solvent, and if it is used instead of water, the solutions will be more concentrated. For medical purposes, alkaloids, thymol, iodine, bromine, etc. are dissolved in it. Glycerin is also used in the preparation of ointments, pastes and creams. It prevents them from drying out. Glycerin itself is an antiseptic.

When reacted with hydrogen chloride, derivatives are obtained that are used as local anesthesia when applied to the skin, as well as for short-term anesthesia for minor surgical interventions, using inhalation.

Alkadienes are alkenes with two double bonds in one molecule. Their main use is the production of synthetic rubber, from which various heating pads and syringes, probes and catheters, gloves, pacifiers and much more are then made, which are simply irreplaceable when caring for the sick.

Industrial Applications

Alkenes and their derivatives have found wider use in industry. (Where and how are alkenes used, table above).

This is only a small part of the use of alkenes and their derivatives. Every year the demand for olefins only increases, which means that the need for their production also increases.

The simplest organic compounds are saturated and unsaturated hydrocarbons. These include substances of the class of alkanes, alkynes, alkenes.

Their formulas include hydrogen and carbon atoms in a certain sequence and quantity. They are often found in nature.

Determination of alkenes

Another name for them is olefins or ethylene hydrocarbons. This is exactly what this class of compounds was called in the 18th century when an oily liquid, ethylene chloride, was discovered.

Alkenes include substances consisting of hydrogen and carbon elements. They belong to acyclic hydrocarbons. Their molecule contains a single double (unsaturated) bond connecting two carbon atoms to each other.

Alkene formulas

Each class of compounds has its own chemical designation. In them, the symbols of the elements of the periodic table indicate the composition and bond structure of each substance.

The general formula of alkenes is denoted as follows: C n H 2n, where the number n is greater than or equal to 2. When deciphering it, it is clear that for each carbon atom there are two hydrogen atoms.

The molecular formulas of alkenes from the homologous series are represented by the following structures: C 2 H 4, C 3 H 6, C 4 H 8, C 5 H 10, C 6 H 12, C 7 H 14, C 8 H 16, C 9 H 18, C10H20. It can be seen that each subsequent hydrocarbon contains one more carbon and 2 more hydrogen.

There is a graphic designation of the location and order of chemical compounds between atoms in a molecule, which is shown by the structural formula of alkenes. Using valence bars, the bond of carbons with hydrogens is indicated.

The structural formula of alkenes can be depicted in expanded form, when all chemical elements and bonds are shown. The more concise expression of olefins does not show the combination of carbon and hydrogen using valence bars.

The skeletal formula denotes the simplest structure. The broken line represents the base of the molecule, in which the carbon atoms are represented by its tips and ends, and the links indicate hydrogen.

How are the names of olefins formed?

CH 3 -HC=CH 2 + H 2 O → CH 3 -OHCH-CH 3.

When alkenes are exposed to sulfuric acid, the process of sulfonation occurs:

CH 3 -HC=CH 2 + HO−OSO−OH → CH 3 -CH 3 CH-O−SO 2 −OH.

The reaction proceeds with the formation of acid esters, for example, isopropyl sulfuric acid.

Alkenes are subject to oxidation during their combustion under the influence of oxygen to form water and carbon dioxide:

2CH 3 -HC=CH 2 + 9O 2 → 6CO 2 + 6H 2 O.

The interaction of olefinic compounds and dilute potassium permanganate in the form of a solution leads to the formation of glycols or alcohols of a diatomic structure. This reaction is also oxidative with the formation of ethylene glycol and discoloration of the solution:

3H 2 C=CH 2 + 4H 2 O+ 2KMnO 4 → 3OHCH-CHOH+ 2MnO 2 +2KOH.

Alkene molecules can be involved in the polymerization process with a free radical or cation-anion mechanism. In the first case, under the influence of peroxides, a polyethylene-type polymer is obtained.

According to the second mechanism, acids act as cationic catalysts, and organometallic substances act as anionic catalysts, releasing a stereoselective polymer.

What are alkanes

They are also called paraffins or saturated acyclic hydrocarbons. They have a linear or branched structure, which contains only saturated simple bonds. All representatives of this class have the general formula C n H 2n+2.

They contain only carbon and hydrogen atoms. The general formula of alkenes is formed from the designation of saturated hydrocarbons.

Names of alkanes and their characteristics

The simplest representative of this class is methane. It is followed by substances such as ethane, propane and butane. Their name is based on the root of the numeral in Greek, to which the suffix -an is added. The names of alkanes are listed in the IUPAC nomenclature.

The general formula of alkenes, alkynes, alkanes includes only two types of atoms. These include the elements carbon and hydrogen. The number of carbon atoms in all three classes is the same, the difference is only in the number of hydrogen, which can be eliminated or added. Unsaturated compounds are obtained from it. Representatives of paraffins contain 2 more hydrogen atoms in their molecule than olefins, which is confirmed by the general formula of alkanes and alkenes. The alkene structure is considered unsaturated due to the presence of a double bond.

If we compare the number of water and carbon atoms in al-cans, then the value will be maximal in comparison with other classes of carbon -ro-dov.

Starting from methane and ending with butane (from C 1 to C 4), substances exist in gaseous form.

Hydrocarbons of the homologous range from C 5 to C 16 are presented in liquid form. Starting with an alkane, which has 17 carbon atoms in the main chain, a transition from the physical state to a solid form occurs.

They are characterized by isomerism in the carbon skeleton and optical modifications of the molecule.

In paraffins, carbon valences are considered to be completely occupied by neighboring carbons or waters with the formation of a σ-type bond. From a chemical point of view, this determines their weak properties, which is why alkanes are called limiting or saturated coals. dovs devoid of affinity.

They undergo substitution reactions associated with radical halogenation, sulfochlorination or nitration of the molecule.

Paraffins undergo a process of oxidation, combustion or decomposition at high temperatures. Under the influence of reaction accelerators, hydrogen atoms are removed or alkanes are dehydrogenated.

What are alkynes

They are also called acetylene hydrocarbons, which have a triple bond in the carbon chain. The structure of alkynes is described by the general formula C n H 2 n-2. It shows that, unlike alkanes, acetylene hydrocarbons lack four hydrogen atoms. They are replaced by a triple bond formed by two π compounds.

This structure determines the chemical properties of this class. The structural formula of alkenes and alkynes clearly shows the unsaturation of their molecules, as well as the presence of a double (H 2 C꞊CH 2) and triple (HC≡CH) bond.

Name of alkynes and their characteristics

The simplest representative is acetylene or HC≡CH. It is also called ethin. It comes from the name of a saturated hydrocarbon, in which the suffix -an is removed and -in is added. In the names of long alkynes, the number indicates the location of the triple bond.

Knowing the structure of saturated and unsaturated hydrocarbons, you can determine which letter indicates the general formula of alkynes: a) CnH2n; c) CnH2n+2; c) CnH2n-2; d) CnH2n-6. The correct answer is the third option.

Starting from acetylene and ending with butane (from C 2 to C 4), the substances are gaseous in nature.

In liquid form there are hydrocarbons of the homologous range from C 5 to C 17. Starting with an alkyne, which has 18 carbon atoms in the main chain, a transition from the physical state to a solid form occurs.

They are characterized by isomerism in the carbon skeleton, in the position of the triple bond, as well as interclass modifications of the molecule.

In terms of chemical characteristics, acetylene hydrocarbons are similar to alkenes.

If alkynes have a terminal triple bond, then they perform the function of an acid with the formation of alkinide salts, for example, NaC≡CNa. The presence of two π bonds makes the sodium acetylidene molecule a strong nucleophile that undergoes substitution reactions.

Acetylene undergoes chlorination in the presence of copper chloride to produce dichloroacetylene, condensation under the action of haloalkynes to release diacetylene molecules.

Alkynes participate in reactions whose principles underlie halogenation, hydrohalogenation, hydration and carbonylation. However, such processes are weaker than in alkenes with a double bond.

For acetylene hydrocarbons, nucleophilic addition reactions of an alcohol, primary amine, or hydrogen sulfide molecule are possible.