Alkanes interact with hydrogen. International Nomenclature of Alkanov. Alkaans: structure, properties. Chemical properties of aromatic hydrocarbons

Limit hydrocarbons are such compounds that are molecules consisting of carbon atoms that are in a state of hybridization SP 3. They are connected with each other exclusively covalent sigma bonds. The name "limit" or "saturated" hydrocarbons proceeds from the fact that these compounds are not able to attach any atoms. They are extremely saturated. The exception is cycloalkanes.

What is alkana?

Alkanians are hydrocarbons of the limit, and their carbon chain is unclipped and consists of carbon atoms interconnected using single ties. It does not contain others (that is, double, like alkenes, or triple, like alkylov) connections. Alkans are also called paraffins. They obtained this name, since well-known paraffins are a mixture of predominantly these limit hydrocarbons with 18 -C 35 with special inertness.

General information about Alkans and their radicals

Their formula: C n p 2 n +2, here n is greater than or equal to 1. The molar mass is calculated by the formula: M \u003d 14N + 2. A characteristic feature: the end in their names is "-an." The remains of their molecules that are formed as a result of replacing hydrogen atoms to other atoms are called aliphatic radicals, or alkyls. They are denoted by the letter R. The general formula for monovalent aliphatic radicals: with n p 2 n +1, here n is greater than or equal to 1. The molar mass of aliphatic radicals is calculated by the formula: M \u003d 14N + 1. The characteristic feature of aliphatic radicals: endings in the names "- Il. Alkanov molecules have their own characteristics of the structure:

• the connection of C-C is characterized by a length of 0.154 nm;
• c-H connection is characterized by a length of 0.109 nm;
• the valence angle (the angle between the bonds of carbon-carbon) is equal to 109 degrees and 28 minutes.

The homologous series of alkanes begin: methane, ethane, propane, butane, and so on.

Physical properties of alkanov

Alkaans are substances that do not have colors and insoluble in water. The temperature in which the alkanes begin to melt, and the temperature at which they boil are rising in accordance with the increase in the molecular weight and the length of the hydrocarbon chain. From less branched to more branched alkanes, the boiling and melting temperature are lowered. Gaseous alkanes are capable of burning a pale blue or colorless flame, while quite a lot of heat stands out. CH 4 -C 4 H 10 is gases that are also absent and the smell. C 5 H 12 -C 15 H 32 is fluids that have a specific odor. From 15 N 32 and so on, these are solids that also do not smell.

Chemical properties of alkanov

These compounds are low-active in a chemical plan, which can be explained by the strength of the hard-refined sigma-links - C-C and C-N. It should also be borne in mind that relations with C - C are non-polar, and Sn is low-polar. These are low-polarizable types of links related to the sigma of appearance and, accordingly, to break the greatest probability they will become a gomolitical mechanism, as a result of which radicals will be formed. Thus, the chemical properties of alkanans are mainly limited to the reactions of radical substitution.

Nuting reactions

Alkans interact only with nitric acid with a concentration of 10% or with a tetraphic nitrogen oxide in a gas medium at a temperature of 140 ° C. The reaction of alkane nitration is called Konovalov's reaction. As a result, nitro compounds and water are formed: CH 4 + nitric acid (diluted) \u003d CH 3 - NO 2 (nitromethane) + water.

Reactions burning

Limit hydrocarbons are very often used as fuel, which is justified by their body ability: with n p 2n + 2 + ((3n + 1) / 2) O 2 \u003d (n + 1) H 2 O + N CO 2.

Oxidation reactions

In the chemical properties of alkanans also includes their ability to oxidation. Depending on which conditions are accompanied by the reaction and how they are changed, can be obtained from the same substance to obtain various end products. The soft oxidation of methane oxygen in the presence of a catalyst that accelerates the reaction, and the temperatures of about 200 ° C may result in the following substances:

1) 2CH 4 (oxygen oxidation) \u003d 2SH 3 it (alcohol - methanol).

2) CH 4 (oxygen oxidation) \u003d CH 2 O (aldehyde - methanal or formaldehyde) + N 2 O.

3) 2CH 4 (oxygen oxidation) \u003d 2NSon (carboxylic acid - methane or formic) + 2N 2 O.

Also, the oxidation of alkanes can be produced in a gaseous or liquid air. Such reactions lead to the formation of higher fatty alcohols and corresponding acids.

Attitude to heating

At temperatures not exceeding + 150-250 ° C, necessarily in the presence of a catalyst, a structural rearrangement of organic substances occurs, which consists in changing the order of the compound of atoms. This process is called isomerization, and substances obtained as a result of the reaction - isomers. Thus, from normal butane it turns out its isomer - isobutane. At temperatures of 300-600 ° C and the presence of the catalyst, there is a rupture of C-H bonds to form hydrogen molecules (dehydrogenation reaction), hydrogen molecules with a carbon chain closure into a cycle (cyclization reaction or alkanov aromatization reactions):

1) 2CH 4 \u003d C 2 H 4 (ethen) + 2n 2.

2) 2CH 4 \u003d C 2 H 2 (ethin) + 3H 2.

3) C 7 H 16 (normal heptane) \u003d C 6 H 5 - CH 3 (toluene) + 4N 2.

Halogenation reactions

Such reactions are in the introduction of halogens (their atoms) in the organic substance molecule, as a result of which the C-halogen connection is formed. In the interaction of alkanes with halogens, halogen derivatives are formed. This reaction has specific features. It proceeds by the mechanism of radical, and to properly proper, it is necessary to effect the halogen and alkanans to affect ultraviolet radiation or simply heat it. The properties of alkanans allow the halogenation reaction to flow until complete substitution for halogen atoms will be achieved. That is, the chlorination of methane will not end with one stage and the production of methyl chloride. The reaction will go further, all possible substitution products will be formed, starting with chloromethane and ending with tetrachloromethane. The effects of chlorine under these conditions on other alkanes will result in the formation of various products obtained as a result of hydrogen replacement in different carbon atoms. From temperature at which the reaction is underway, the ratio of finite products and the speed of their formation will depend. The longer the hydrocarbon chain of alkane, the easier it will be to go this reaction. When halogenation, the carbon atom will first be replaced with the least hydrogenated (tertiary). Primary will enter the reaction after all others. Halogenation reaction will occur in stages. On the first stage, only one hydrogen atom is substituted. With halogen solutions (chlorine and bromine water), alkanes do not interact.

Sulfooling reactions

The chemical properties of alkanans are also complemented by the sulfooling reaction (it is called the reaction of the reaction). When exposed to ultraviolet radiation, the alkanes are capable of reacting with a mixture of chlorine and sulfur dioxide. As a result, chloride is formed, as well as an alkyl radical, which joins sulfur dioxide. As a result, a complex compound is obtained, which becomes stable due to the capture of the chlorine atom and the destruction of its one molecule: R-H + SO 2 + Cl 2 + ultraviolet radiation \u003d R-SO 2 CL + HCl. The sulfonyl chlorides formed as a result of the reaction are widely used in the production of surfactants.

The simplest organic compounds are hydrocarbonsconsisting of carbon and hydrogen. Depending on the nature of chemical bonds in hydrocarbons and the relationship between carbon and hydrogen, they are divided into limiting and unforeseen (alkenes, alkins, etc.)

Limithydrocarbons (alkanes, hydrocarbons of the methane row) are the compounds of carbon with hydrogen, in molecules of which each carbon atom spends on a compound with any other neighboring atom of no more than one valence, and all the valence not allowed to be connected to hydrogen carbon. All carbon atoms in alkanes are in SP 3 - condition. Limit hydrocarbons form a homologous series characterized by the general formula FROM n. N. 2N + 2. . The twin priority of this series is methane.

Isomeria. Nomenclature.

Alkans with n \u003d 1,2,3 may exist only in the form of one isomer

Starting with n \u003d 4, the phenomenon of structural isomerism appears.

The number of structural isomers of alkanes is growing rapidly with an increase in the number of carbon atoms, for example, pentane has 3 isomers, heptane - 9, etc.

The number of alkane isomers increases and due to possible stereoisomers. Starting with C 7 N 16, the existence of chiral molecules that form two enantiomers are possible.

Nomenclature of alkanes.

The dominant nomenclature is the IUPAC nomenclature. At the same time, it present elements of trivial names. Thus, the first four members of the homologous series of alkanes have trivial names.

CH 4 - methane

From 2N 6 - ethane

C 3 H 8 - Propane

With 4 H 10 - Bhutan.

The names of the remaining homologues are formed from Greek Latin numerical. So, for the following members of a number of normal (unbranched) build, names are used:

From 5 H 12 - Pentan, from 6 H 14 - hexane, from 7 H 18 - heptane,

From 14 H 30 - Tetradecan, from 15 H 32 - pentadecan, etc.

Basic rules of IUPAC for branched alkanov

a) Choose the longest unbranched chain, the name of which is the basis (root). This basis add suffix "An"

b) number this chain on the principle of least lockers,

c) The substituent indicates as prefixes in alphabetical order indicating the location of the location. If there are several identical substituents in the spring structure, then their number indicate the Greek numerical.

Depending on the number of other carbon atoms with which the carbon atom is directly connected, distinguished: primary, secondary, tertiary and quaternary carbon atoms.

Alkyl groups or alkyl radicals are described as substituents in branched alkans, which are considered as the result of the deduction from the alkane molecule of one hydrogen atom.

The name of alkyl groups form from the name of the corresponding alkanes by replacing the last suffix "AN" to the soffix "Il".

CH 3 - Methyl

CH 3 CH 2 - ethyl

CH 3 CH 2 CH 2 - Propil

For the name of branched alkyl groups, the numbering of the chain is also used:

Starting with ethane, alkanes are capable of forming conformers, which correspond to the inhibited conformation. The possibility of transition of one inhibited conformation to another through the obscured is determined by the barrier of rotation. Determining the structure, composition of conformers and rotation barriers are the tasks of conformational analysis. Methods for obtaining alkanes.

1. Fractional distillation of natural gas or gasoline oil fraction.In this way, individual alkanes can be separated to 11 carbon atoms.

2. Hydrogenation of coal.The process is carried out in the presence of catalysts (oxides and sulfides of molybdenum, tungsten, nickel) at 450-470 ° C and pressures up to 30 MPa. Coal and catalyst are triturated in powder and hydrogenated hydrogenated, strubbing hydrogen through a suspension. The resulting mixtures of alkanes and cycloalkanes are used as a motor fuel.

3. Hydrogenation co and with 2 .

CO + H 2  Alkanes

CO 2 + H 2  Alkanes

CO, FE, and others are used as catalysts of these reactions. D - elements.

4. Hydrogenation of alkenes and alkins.

5. Metalorganic synthesis.

but). Synthesis of Watza.

2RHAL + 2NA  R R + 2NAHAL

This synthesis is unsuitable if two different halolennas are used as organic reagents.

b). Protolysis of Grignar reagents.

R HAL + MG  Rmghal

Rmghal + HOH  RH + MG (OH) HAL

in). Interaction of lithium dialkiprats (LIR 2 Cu) with alkyl halides

LIR 2 CU + R X  R R + RCU + LIX

Lithium dialkiprats themselves are obtained by a two-stage method.

2R Li + Cui  LIR 2 CU + LII

6. Electrolysis of carboxylic salts (Sintez Kolbe).

2RCoona + 2H 2 O  R R + 2CO 2 + 2NAOH + H 2

7. Roll of carboxylic acid salts with alkalis.

The reaction is used to synthesize lower alkanes.

8. Hydrogenolysis of carbonyl compounds and halolyanov.

but). Carbonyl compounds. Synthesis of Clement.

b). Halogens. Catalytic hydrogenolysis.

Ni, Pt, Pd are used as catalysts.

c) Halogens. Reagent recovery.

RHAL + 2HI  RH + HHAL + I 2

Chemical properties of alkanes.

All connections in alkanes are low-polar, on this they are characterized by radical reactions. The absence of PI bonds makes it impossible to the reaction of attachment. For alkanans, the reaction of substitution, cleavage, combustion is characteristic.

Halogenation reaction mechanism:

Haloiding

Halogenation of alkanes proceeds through a radical mechanism. To initiate the reaction, a mixture of alkane and halogen is necessary to irradiate UV light or heat. Methane chlorination does not stop at the stage of obtaining methyl chloride (if equimolar amounts of chlorine and methane are taken), and leads to the formation of all possible substitution products, from methyl chloride to tetrachloroupar. Chlorination of other alkanes leads to a mixture of hydrogen replacement products in different carbon atoms. The ratio of chlorination products depends on temperature. The rate of chlorination of primary, secondary and tertiary atoms depends on the temperature, at low temperatures, the speed decreases in the row: tertiary, secondary, primary. With increasing temperature, the difference between speeds decreases until it becomes the same. In addition to the kinetic factor, the distribution of chlorination products has an impact of a statistical factor: the probability of the chlorine attack is 3 times less than primary and twice as secondary. Thus, the chlorination of alkanes is a non-stero-selective reaction, eliminating cases when only one monochlorination product is possible.

Halogenation is one of the reactions of substitution. Alkanov's halogenation obeys the rule of the Markovnik (Markovnikov Rules) - primarily halogenated the least hydrogenated carbon atom. Alkanan halogenation passes in gradually - in one stage, no more than one hydrogen atom is halogenated.

CH 4 + CL 2 → CH 3 CL + HCl (chloromethane)

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

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

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

Under the action of light, the chlorine molecule decays to atoms, then they attack methane molecules, tearing at the hydrogen atom, as a result, methyl radicals are formed, which are faced with chlorine molecules, destroying them and forming new radicals.

Nitching (Konovalov reaction)

Alkans are reacting with a 10% nitric acid solution or nitrogen oxide N 2 O 4 in the gas phase at a temperature of 140 ° and a slight pressure with the formation of nitro-producing. The reaction also obeys the rule of Markovnikov.

RH + HNO 3 \u003d RNO 2 + H 2 O

i.e. one of the hydrogen atoms is replaced by the residue NO 2 (ni-trogroup) and water is distinguished.

The features of the structure of the isomers are strongly reflected during the course of this reaction, since it is easiest to substitute hydrogen atom in the nitro group in the SI residue (existing only in some isomers), the hydrogen in the CH 2 group is less easily, and even more difficult - in the remnant CH 3.

Paraffins are fairly easy to wear out in the gas phase at 150-475 ° C of nitrogen dioxide or nitric acid pairs; In this case, it happens in part and. oxidation. The threading of methane is almost exclusively nitromethane:

All available data indicate a free radical mechanism. As a result of the reaction, mixtures of products are formed. Nitric acid at ordinary temperature almost does not act on paraffin hydrocarbons. When heated, it acts mainly as an oxidizing agent. However, as I found M. I. Konovalov (1889), with heating nitric acid acts in part and "the strain" manner; The reaction of nitration with weak nitric acid is particularly well under heating and elevated pressure. The reaction of the nitration is expressed by the equation.

Following the methane, homologues give a mixture of different nitroparaphins due to the passing splitting. When nitrogenation of ethane is obtained nitroetan CH 3 -CH 2 -NO 2 and nitromethane CH 3 -NO 2. A mixture of nitroparaffins is formed from the propane:

Nuting paraffins in the gas phase is now carried out on an industrial scale.

Sulfooling:

An important reaction is sulfocyloration of alkanans. When the alkane interacts with chlorine and sulfur arhydride, hydrogen is replaced with a chlorosulfonyl group:

Stages of this reaction:

CL + R: H → R + HCl

R + SO 2 → RSO 2

RSO 2 + CL: CL → RSO 2 Cl + Cl

Alcanofochlorides are easily hydrolyzed to the alkanesulfoxylost (RSO 2 OH), the sodium salts of which (RSO 3¯ Na + - Sodium Alkanfonate) exhibit properties similar to soams and are used as determinents.

Physical properties. Under normal conditions, the first four members of the homologous series of alkanans (from 1 - with 4) are gases. Normal alkanes from Pentane to Heptadecan (C 5 - C 17 ) - liquids, starting with from 18 and above - solids. As the number of carbon atoms increases in the chain, i.e. With increasing relative molecular weight, the boiling and melting temperature of alkanes increase. With the same number of carbon atoms in the alkaved alkane molecule with a branched structure, there are lower boiling points than normal alkanes.

Alkana Practically insoluble in water, since their molecules are low-polar and do not interact with water molecules, they are well soluble in non-polar organic solvents, such as benzene, tetrachloromethane, etc. Liquid alkanes are easily mixed with each other.

The main natural sources of alkanan - oil and natural gas. Various oil fractions contain alkanes fromC 5 H 12 up to 30 H 62. Natural gas consists of methane (95%) with an admixture of ethane and propane.

Of synthetic methods of obtainingalkanov You can select the following: /\u003e

one . Obtaining from unsaturated hydrocarbons. The interaction of alkenes or alkins with hydrogen ("hydrogenation") occurs in the presence of metal catalysts (/\u003e Ni, Pd ) As
heating:

CH W - C ≡SN + 2N 2 → CH 3 -CH 2 -CH 3.

2. Getting out halogenproducts. When heating the monogalogen-substituted alkanans with a metal sodium, alkanes are obtained with a twin-number carbon atoms (Würtz reaction): /\u003e

C 2 H 5 BR + 2 NA + BR - C 2 H 5 → C 2 H 5 - C 2 H 5 + 2 Nabr..

This reaction is not carried out with two different halogen-substituted Alkanians, because it turns out a mixture of three different alkanans

3. Obtaining carboxylic acid salts. When fusing anhydrous carboxylic acid salts with alkalis, alkanes are obtained containing one carbon atom less than the carbon chain of the original carboxylic acids: /\u003e

4. Methane. In the electrical arc burning in the atmosphere of hydrogen, a significant amount of methane is formed: /\u003e

C + 2N 2 → CH 4 .

The same reaction comes with carbon heating in a hydrogen atmosphere to 400-500 ° C at elevated pressure in the presence of a catalyst.

In laboratory conditions, methane is often obtained from aluminum carbide:

A L 4. C 3 + 12N 2 O \u003d ZSN 4 + 4Al (OH) 3.

Chemical properties. Under normal conditions, alkanes are chemically inert. They are resistant to many reagents: do not interact with concentrated sulfur and nitric acids, with concentrated and molten alkalis, are not oxidized by strong oxidizers - potassium permanganateKMN.About 4, etc.

Chemical stability of alkanes is due to high strengths -c-S and C-N connections, as well as their non-polarity. Non-polar bonds C-C and C-H in alkanes are not prone to ion rupture, but are able to split down homologies under the influence of active free radicals. Therefore, radical reactions are characteristic of alkanans, as a result of which compounds are obtained, where hydrogen atoms are substituted with other atoms or groups of atoms. Consequently, the alkanes enter the reaction flowing through the mechanism of radical substitution denoted by the symbolS R ( from Englishsubstitution. radicalic). Under this mechanism, hydrogen atoms in tertiary, then at secondary and primary carbon atoms are then replaced.

1. Halogenation. When the interaction of alkanans with halogens (chlorine and bromom) under the action of UV radiation or high temperature, a mixture of products from mono- polyhalogen-substituted Alkanans. The overall diagram of this reaction is shown on the example of methane: /\u003e

b) chain growth. The radical of chlorine takes a hydrogen atom at the alkane molecule:

Cl.· + CH 4 → NA /\u003e L + CH 3 ·

At the same time, an alkyl radical is formed, which takes the chlorine atom at the chlorine molecule:

CH 3 · + C L 2 → CH 3 with L + C l.·

These reactions are repeated until the circuit breaks down according to one of the reactions:

Cl.· + Cl.· → with L /\u003e 2, CH 3 · + CH 3 · → C 2 H 6, CH 3 · + Cl.· → CH 3 with L ·

Total reaction equation:

The forming chloromethane may be subjected to further chlorination, giving a mixture of productsCH 2 Cl. 2, CHCl 3, SS L 4 according to the scheme (*).

The development of chain theory free radical Reactions are closely related to the name of an outstanding Russian scientist, the Nobel Prize laureate N.I. Semenova (1896-1986).

2. Nuting (Konovalov Reaction). Under the action of dilute nitric acid to alkanes at 140 ° C and a low pressure flows a radical reaction: /\u003e

With radical reactions (halogenation, nitration), hydrogen atoms in tertiary, then at secondary and primary carbon atoms are mixed. This is explained by the fact that the lighter of the tertiary carbon atom with hydrogen (bonding energy 376 (390 kJ / mol), and only then - primary (415 kJ / mol), is then easiest.

3. Isomerization. Normal alkanes under certain conditions can turn into alkanes with a branched chain: /\u003e

4. Claking is a hemolytic rupture of C-C connections, which flows when heated and under the action of catalysts.
At the cracking of the highest alkans, alkenes and lower alkanes are formed, acetylene is formed during the cracking of methane and ethane: /\u003e

C /\u003e 8 H 18 → C 4 H 10 + C 4N 8, /\u003e

2SH 4 → C 2 H 2 + ZN 2,

C 2 H 6 → C 2 H 2 + 2N 2.

These reactions have a large industrial value. In this way, high-boiling oil fractions (fuel oil) are converted into gasoline, kerosene and other valuable products.

5. Oxidation. With the mild oxidation of methane oxygen in the presence of various catalysts, methyl alcohol, formaldehyde, formic acid can be obtained:

Soft catalytic oxidation of butane air oxygen - one of the industrial methods for producing acetic acid:

t.°
2 C 4 /\u003e H /\u003e 10 + 5 O /\u003e 2 → 4 CH /\u003e 3 COOH /\u003e + 2N 2 O .
Cat.

On the air Alkana burn to CO 2 and H 2 O: /\u003e

With n 2 n +2 + (s n.+1) / 2O 2 \u003d N with 2 + (n +1) H 2 O.

Alkaans (limiting hydrocarbons, paraffins)

• Alkana - aliphatic (acyclic) extreme hydrocarbons in which carbon atoms are interconnected by simple (single) connections in unbranched or branched chains.

Alkana - The name of limit hydrocarbons on international nomenclature.
Paraffins- Historically established name, reflecting the properties of these compounds (from lat. parrum affinis - having little affinity, lowactive).
Limit, or saturatedThese hydrocarbons are called due to the full saturation of the carbon chain atoms of hydrogen.

The simplest representatives of Alkanov:

Molecules models:

When comparing these compounds it is clear that they differ from each other for the group. -CH 2 - (methylene). Adding another group to the propane -CH 2 -, I get Bhutan From 4 H 10, then alkana From 5 n 12, From 6 H 14 etc.

Now you can withdraw the general formula of alkanans. The number of carbon atoms in a row of alkanov we will take n. , then the number of hydrogen atoms will be the magnitude 2N + 2. . Consequently, the composition of alkanov corresponds to the general formula C n h 2n + 2.
Therefore, such a definition is used:

Alkana - hydrocarbons whose composition is expressed by the general formula C n h 2n + 2where n. - The number of carbon atoms.

The structure of alkanan

Chemical structure (The order of compounds of atoms in molecules) of the simplest alkanes - methane, ethane and propane - show their structural formulas, shown in Section 2. From these formulas it is clear that there are two types of chemical ties in alkanes:

C-S. and C-N..

Communication C-C is a covalent non-polar. Communication C - H is a covalent weaklyolar, because Carbon and hydrogen are close by electronegability (2.5 - for carbon and 2.1 - for hydrogen). The formation of covalent bonds in alkanes due to the general electronic pairs of carbon and hydrogen atoms can be shown using electronic formulas:

Electronic and structural formulas reflect chemical structurebut do not give ideas about the spatial structure of moleculeswhich significantly affects the properties of the substance.

Spatial structure. The relative arrangement of the molecule atoms in space depends on the direction of atomic orbitals (AO) of these atoms. In hydrocarbons, the main role is played by the spatial orientation of carbon orbitals, since the spherical 1S-AO of the hydrogen atom is deprived of a certain orientation.

The spatial arrangement of carbon AO in turn depends on the type of hybridization (part I, section 4.3). A rich carbon atom in alkanes is associated with four other atoms. Consequently, its state corresponds to SP 3-hybridization (part I, section 4.3.1). In this case, each of the four SP 3-hybrid carbon Ao is involved in the axial (σ-) overlapping from S-AO hydrogen or with SP 3 -AO of another carbon atom, forming σ-bond with S-H or C-C.

Four σ-bonds of carbon are directed in space at an angle of 109 ° C 28 ", which corresponds to the smallest repulsion of electrons. Therefore, the molecule of the simplest representative of alkanes - methane CH 4 - has the form of a tetrahedron, in the center of which there is a carbon atoms, and at the vertices - hydrogen atoms:

The valence corner of the N-C-N is 109 о 28 ". The spatial structure of methane can be shown using bulk (scale) and scaleline models.

For recording it is convenient to use a spatial (stereoochemical) formula.

In the molecule of the next homologist - ethane with 2 H 6 - two tetrahedral sp. 3 carbon mats form a more complex spatial structure:

For alkanov molecules containing over 2 carbon atoms, curved forms are characteristic. This can be shown on the example n.-Butan (VRML model) or n.-Penta:

Isomeriya Alkanov

• Isomerius - the appearance of the compounds that have the same composition (the same molecular formula), but a different structure. Such compounds are called isomaers.

Differences in the order of the compound of atoms in molecules (i.e. in the chemical structure) lead to structural isomeria. The structure of structural isomers is reflected by structural formulas. In a number of alkanans, structural isomerism is manifested when the content of 4 and more carbon atoms in the circuit is, i.e. Starting with Bhutan with 4 H 10.
If in molecules of the same composition and the same chemical structure, various mutual arrangement of atoms in space is possible, then observed spatial isomerism (stereoisomeria). In this case, the use of structural formulas is not enough and models of molecules or special formulas should be used - stereochemical (spatial) or projection.

Alkanes, starting with Ethane H 3 C-CH 3, exist in various spatial forms ( conformations) due to intramolecular rotation of σ-links C-C, and manifest the so-called rotary (conformational) isomerism.

In addition, if there is a carbon atom in the molecule associated with 4 different substituents, another type of spatial isomerism is possible, when two stereoisomers belong to each other as an object and its mirror image (just as the left hand refers to the right). Such differences in the structure of molecules are called optical isomeria.

Structural isomeria Alkanov

• Structural isomers - compounds of the same composition, characterized by the procedure for binding atoms, i.e. Chemical structure of molecules.

The cause of the manifestation of structural isomerism in a row of alkans is the equipment of carbon atoms to form circuits of various structures. This type of structural isomerism is called isomeria carbon skeleton.

For example, Alkan composition C 4 H 10 may exist as two Structural isomers:

and Alkan C 5 H 12 - in the form three structural isomers, characterized by the structure of the carbon chain:

With an increase in the number of carbon atoms in the composition of molecules, the possibilities for branching the chain, i.e. The amount of isomers is growing a threshold of the number of carbon atoms.

Structural isomers are distinguished by physical properties. Alkanes with a branched structure due to less dense packaging of molecules and, accordingly, smaller intermolecular interactions, boil the temperature than their unbranched isomers.

In the output of the structural formulas of the isomers, the following techniques use.

Hydrocarbons are the simplest organic compounds. They are carbon and hydrogen. The compounds of these two elements are called limit hydrocarbons or alkanes. Their composition is expressed in general for alkanes with the CNH2N + 2 formula, where N is the number of carbon atoms.

In contact with

Odnoklassniki.

Alkana - International Name of Data Compounds. Also, these compounds are called paraffins and saturated hydrocarbons. Communication in alkanan molecules is simple (or single). The remaining valence is saturated with hydrogen atoms. All alkanes are saturated with hydrogen to the limit, its atoms are in a state of SP3 hybridization.

Homological range of limiting hydrocarbons

The first in the homologous row of saturated hydrocarbons is methane. His formula CH4. The end is -an in the name of limiting hydrocarbons, it is a distinctive feature. Next, in accordance with the above formula, ethane - C2H6 are located in a homologous series, C3H8 propane, butane - C4H10.

From the fifth alkana The homologous series of the titles of the compounds are formed as follows: the Greek number indicating the number of hydrocarbon atoms in the molecule + end -an. So, in Garcaries, the number 5 - Pande, respectively, the pentan - C5H12 goes for Bhutan. Next - Hexane C6H14. Heptane - C7H16, Octan - C8H18, Nonane - C9H20, Dean - C10H22, etc.

The physical properties of alkanans change markedly in the homologous series: the melting point, boiling point increases, the density increases. Methane, ethane, propane, butane under normal conditions, i.e. at a temperature of approximately 22 degrees of heat Celsius, are gases, with pentane on hexadecan inclusive - liquids, with heptadecan - solids. Starting with Bhutan, Alkanan has isomers.

There are tables reflecting changes in the homologous row of alkananswhich clearly reflect their physical properties.

Nomenclature of saturated hydrocarbons, their derivatives

If the hydrogen atom is separated from the hydrocarbon molecule, monovalent particles are formed, which are called radicals (R). The name of the radical gives the hydrocarbon, from which this radical is produced, while the end -ann changes to the end-in. For example, a radical methyl radical is formed from methane during the separation of the hydrogen atom, from the ethane - ethyl, from propane - propyl, etc.

Radicals are also formed inorganic compounds. For example, at a nitric acid, it is possible to obtain a monovalent radical -no2 radical, which is called a nitroup.

When separating from the molecule Alkan two hydrogen atoms are formed by bivalent radicals, the names of which are also formed from the name of the corresponding hydrocarbons, but the ending changes to:

• orin, in the event that hydrogen atoms are torn off from one carbon atom,
• iLEN, in the event that the two hydrogen atoms are torn off from two neighboring carbon atoms.

Alkana: Chemical properties

Consider the reactions characteristic of alkanans. All alkanes are inherent in general chemical properties. These substances are low-active.

All known reactions involving hydrocarbons are divided into two types:

• communication S-H (an example is a substitution reaction);
• communication gap C-C (cracking, formation of individual parts).

Very active at the moment of radical formation. By themselves, they exist shares of seconds. Radicals easily enter the reaction among themselves. Their unpaired electrons form a new covalent connection. Example: CH3 + CH3 → C2H6

Radicals easily enter the reaction with organic molecules. They are either joined to them, or be separated from them an impermerable electron from them, as a result of which new radicals appear, which, in turn, can enter into reactions with other molecules. With such a chain reaction, macromolecules are obtained, which cease to grow only when the chain breaks (Example: the connection of two radicals)

The reactions of free radicals explain many important chemical processes, such as:

• Explosions;
• Oxidation;
• Cracking oil;
• Polymerization of unsaturated compounds.

Detail consider chemical properties Saturated hydrocarbons on the example of methane. We have already considered the structure of the alkane molecule. Carbon atoms are located in the methane molecule in the state of SP3 hybridization, and a rather durable connection is formed. Methane is a gas base of smell and colors. It is easier than air. In water a little solvent.

Alkana can burn. Methane is burning with a blue flame. In this case, the result of the reaction will be carbon monoxide and water. When mixed with air, as well as in a mixture with oxygen, especially if the ratio of volumes is 1: 2, the data of the hydrocarbon forms explosive mixtures, which is why it is extremely dangerous for use in everyday life and mines. If methane burns not completely, soot is formed. In industry, it is thus obtained.

Formaldehyde and methyl alcohol are obtained from methane by oxidation in the presence of catalysts. If methane is heavily heat, it disintegrates by the CH4 → C + 2H2 formula

Methane decay You can implement to the intermediate product in specially equipped furnaces. An intermediate product will be acetylene. Reaction formula 2CH4 → C2H2 + 3H2. The release of acetylene from methane reduces production costs almost twice.

Also, hydrogen is also obtained from methane, producing conversion of methane with water vapor. Characteristic for methane are reactions of substitution. So, at a conventional temperature, hydrogen from methane molecule is displaced at the light of halogen (CL, BR). Thus, substances are formed, called halogen derivatives. Chlorine atoms, replacing hydrogen atoms in the hydrocarbon molecule, form a mixture of different connections.

In such a mixture there are chloromethane (CH3 CL or methyl chloride), dichloromethane (CH2Cl2Ili methylene chloride), trichloromethane (CHCl3 or chloroform), tetrachloromethane (CCl4 or carbon tetrachloride).

Any of these compounds can be isolated from the mixture. In production, chloroform and tetrachloromethane are imported importance, due to the fact that they are solvents of organic compounds (fat, resins, rubber). Halogen derivatives are formed by a chain free radical mechanism.

Light affects chlorine molecules, as a result of which they disintegrate The inorganic radicals that tear the hydrogen atom with one electron from the methane molecule. At the same time, HCl and methyl are formed. Methyl reacts with chlorine molecule, resulting in a halogen derivative and chlorine radical. Next, the chlorine radical continues the chain reaction.

At normal temperatures, methane has sufficient resistance to alkalis, acids, many oxidizers. Exception - nitric acid. The reaction with it is formed nitromethane and water.

Connection reactions for methane are not characteristic, since all valences in its molecule are saturated.

The reactions in which hydrocarbons can take place not only with the splitting of the C-H connection, but also with the breakdown of C-s. Such transformations occur in the presence of high temperatures. and catalysts. Such reactions include dehydrogenation and cracking.

Of the saturated hydrocarbons by oxidation, acids are obtained - acetic (from butane), fatty acids (from paraffin).

Obtaining methane

In nature methane Wide widespread. It is the main component of the majority of combustible natural and artificial gases. It is distinguished from coal reservoirs in the mines, from the bottom of the swamp. Natural gases (which is very noticeable in associated gases of petroleum fields) contain not only methane, but also other alkanes. The use of these substances is varied. They are used as fuel, in various industries, in medicine and technology.

Under the laboratory conditions, this gas is isolated when the mixture is heated by sodium acetate + sodium hydroxide, as well as the reaction of aluminum and water carbide. Also methane is obtained from simple substances. For this mandatory conditions are heating and catalyst. Industrial importance is obtaining methane synthesis based on water vapor.

Methane and its homologs can be obtained by calcining salts of appropriate organic acids with alkalis. Another way to obtain alkanans is the reaction of the Würz, at which the monogalogenic production with metal sodium is heated.