Hydrocarbons, in the molecules of which the atoms are linked by single bonds and which correspond to the general formula C n H 2 n +2.
In alkane molecules, all carbon atoms are in the sp 3 -hybridization state. This means that all four hybrid orbitals of the carbon atom are the same in shape, energy and are directed to the corners of an equilateral triangular pyramid - a tetrahedron. The angles between the orbitals are 109 ° 28 ′.

Almost free rotation is possible around a single carbon-carbon bond, and alkane molecules can acquire a wide variety of shapes with angles at carbon atoms close to tetrahedral (109 ° 28 ′), for example, in a molecule n-pentane.

It is especially worth recalling the bonds in alkane molecules. All bonds in the molecules of saturated hydrocarbons are single. Overlapping occurs along the axis,
connecting the nuclei of atoms, that is, these are σ-bonds. Carbon-carbon bonds are non-polar and poorly polarizable. The length of the C-C bond in alkanes is 0.154 nm (1.54 10 - 10 m). The CH bonds are somewhat shorter. The electron density is slightly shifted towards the more electronegative carbon atom, i.e. the CH bond is weakly polar.

The absence of polar bonds in the molecules of saturated hydrocarbons leads to the fact that they are poorly soluble in water and do not interact with charged particles (ions). The most typical reactions for alkanes are reactions involving free radicals.

Homologous series of methane

Homologues- substances similar in structure and properties and differing by one or more CH 2 groups.

Isomerism and nomenclature

The so-called structural isomerism is characteristic of alkanes. Structural isomers differ from each other in the structure of the carbon skeleton. The simplest alkane with structural isomers is butane.

Nomenclature basics

1. Selection of the main circuit. The formation of the name of a hydrocarbon begins with the definition of the main chain - the longest chain of carbon atoms in a molecule, which is, as it were, its basis.
2. Numbering of the atoms of the main chain. The atoms in the main chain are assigned numbers. The numbering of the atoms of the main chain begins from the end to which the substituent is closer (structures A, B). If the substituents are at an equal distance from the end of the chain, then the numbering starts from the end at which there are more of them (structure B). If various substituents are at an equal distance from the ends of the chain, then the numbering begins from the end to which the older one is closer (structure D). The precedence of hydrocarbon substituents is determined by the order in which the letter follows in the alphabet with which their name begins: methyl (-CH 3), then ethyl (-CH 2 -CH 3), propyl (-CH 2 -CH 2 -CH 3 ) etc.
Please note that the name of the substitute is formed by replacing the suffix -an with the suffix - silt in the name of the corresponding alkane.
3. Name formation... At the beginning of the name, they indicate numbers - the numbers of carbon atoms at which the substituents are located. If there are several substituents on a given atom, then the corresponding number in the name is repeated twice, separated by commas (2,2-). After the number, the number of substituents is indicated with a hyphen ( di- two, three- three, tetra- four, penta- five) and the name of the substituent (methyl, ethyl, propyl). Then, without spaces or hyphens, the name of the main chain. The main chain is called as a hydrocarbon - a member of the homologous series of methane ( methane CH 4, ethane C 2 H 6, propane C 3 H 8, C 4 H 10, pentane C 5 H 12, hexane C 6 H 14, heptane C 7 H 16, octane C 8 H 18, nonan C 9 H 20, dean C 10 H 22).

Physical properties of alkanes

The first four representatives of the homologous series of methane are gases. The simplest of them - methane - a gas without color, taste and smell (the smell of "gas", having felt which, you need to call 04, is determined by the smell of mercaptans - sulfur-containing compounds, specially added to methane used in household and industrial gas appliances so that people those near them could smell the leak).
Hydrocarbons of composition from C 4 H 12 to C 15 H 32 - liquids; heavier hydrocarbons are solids. The boiling and melting points of alkanes gradually increase with increasing carbon chain length. All hydrocarbons are poorly soluble in water, liquid hydrocarbons are common organic solvents.

Chemical properties of alkanes

Substitution reactions.
The most typical reactions for alkanes are free radical substitution reactions, during which a hydrogen atom is replaced by a halogen atom or some group. Let us present the equations of characteristic reactions halogenation:


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

The resulting substances are widely used as solvents and starting materials in organic syntheses.
Dehydrogenation reaction(hydrogen abstraction).
In the course of passing alkanes over the catalyst (Pt, Ni, A1 2 0 3, Cr 2 0 3) at a high temperature (400-600 ° C), a hydrogen molecule is eliminated and an alkene is formed:


Reactions accompanied by the destruction of the carbon chain.
All saturated hydrocarbons burn to form carbon dioxide and water. Gaseous hydrocarbons mixed with air in certain proportions can explode.
1. Combustion of saturated hydrocarbons is a free radical exothermic reaction that is very important when using alkanes as fuel:

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

2. Thermal decomposition of hydrocarbons.

The process proceeds according to a free radical mechanism. An increase in temperature leads to homolytic rupture of the carbon-carbon bond and the formation of free radicals.

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

Thermal cleavage reactions are at the heart of the industrial process - the cracking of hydrocarbons. This process is the most important stage in oil refining.

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

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

4. Isomerization... When linear hydrocarbons are heated with an isomerization catalyst (aluminum chloride), substances with a branched carbon skeleton are formed:

5. Aromatization... Alkanes with six or more carbon atoms in the chain in the presence of a catalyst cyclize to form benzene and its derivatives:

Alkanes enter into reactions proceeding according to a free radical mechanism, since all carbon atoms in alkane molecules are in the sp 3 -hybridization state. The molecules of these substances are built using covalent non-polar C-C (carbon-carbon) bonds and weakly polar C-H (carbon-hydrogen) bonds. They do not contain areas with increased and decreased electron density, easily polarizable bonds, i.e., such bonds in which the electron density can shift under the influence of external factors (electrostatic fields of ions). Consequently, alkanes will not react with charged particles, since bonds in alkane molecules are not broken by a heterolytic mechanism.

) are characterized by the suffix -an... The first four hydrocarbons have historical names; starting with the fifth, the name of the hydrocarbon is based on the Greek name for the corresponding number of carbon atoms. Hydrocarbons in which all carbon atoms are located in one chain are called normal. Normal chain hydrocarbons have the following names:

Branched chain hydrocarbons are named as follows

1 ... The name of this compound is based on the name of the hydrocarbon corresponding to the number of carbon atoms in the main chain:

• the main chain of carbon atoms is considered the longest;
• if two or more equally long chains can be distinguished in a hydrocarbon, then the one that has the greatest number of branches is chosen as the main one.

2 ... Once the main chain has been established, the carbon atoms must be numbered. The numbering begins from the end of the chain to which any of the alkyls is closer. If different alkyls are at an equal distance from both ends of the chain, then the numbering starts from the end to which the radical with a lower number of carbon atoms is closer (methyl, ethyl, propyl, etc.).

2,2,4-trimethylpent an

Not right! Radicals are named alphabetically! 2.3 - If two or more side chains of different nature are present, they are cited in alphabetical order. (http://www.acdlabs.com/iupac/nomenclature/79/r79_36.htm) If the same radicals that determine the beginning of the numbering are at an equal distance from both ends of the chain, but there are more of them on one side than on the other, the numbering starts from the end where the number of branches is greater.
When naming a compound, the substituents are first listed in alphabetical order (numerals are not taken into account), and the number corresponding to the number of the carbon atom of the main chain at which this radical is located is placed in front of the name of the radical. After that, the hydrocarbon corresponding to the main chain of carbon atoms is called, separating the word from the numbers with a hyphen.

If a hydrocarbon contains several identical radicals, then their number is denoted by a Greek numeral (di, three, tetra, etc.) and placed in front of the name of these radicals, and their position is indicated, as usual, in numbers, and the numbers are separated by commas, in order their ascents and put before the name of the given radicals, separating them from it with a hyphen. For the simplest hydrocarbons of the iso-structure, their non-systematic names ( isobutane, isopentane, neopentane, isohexane).

Radicals are named, replacing the suffix -an in the name of the hydrocarbon on -il:

Name amyl for the radical C 5 H 11 is no longer applied.

When constructing the name of complex radicals, the numbering of their atoms begins from a carbon atom with a free valence.
Divalent radicals are named by adding the suffix to the name of the hydrocarbon -ilen(except for "methylene").

see also

Wikimedia Foundation. 2010.

See what the "Systematic nomenclature of alkanes" is in other dictionaries:

The first homologue of benzene, methylbenzene, or toluene, C7H8 has no position isomers, like all monosubstituted derivatives. The second homologue C8H10 can exist in four forms: ethylbenzene C6H5 C2H5 and three dimethylbenzene, or xylene, ... ... Wikipedia

In accordance with the IUPAC rules, when constructing alkenes, the longest carbon chain containing a double bond is named the corresponding alkane, in which the suffix an is replaced by en. Butene 1 (butylene 1) This chain is numbered like this ... ... Wikipedia

The International Union of Pure and Applied Chemistry (IUPAC) (IUPAC) has recommended for use a nomenclature called the IUPAC nomenclature. Earlier, the Geneva nomenclature was widespread. The IUPAC rules are published in ... ... Wikipedia

This article is about chemical compounds. For the Canadian aluminum company see Rio Tinto Alcan ... Wikipedia

A distinctive feature of alcohols is the hydroxyl group at a saturated carbon atom in the figure highlighted in red (oxygen) and gray (hydrogen). Alcohols (from lat. ... Wikipedia

This article is about chemical compounds. For an article about the Canadian aluminum company Alcan, see linear or branched acyclic hydrocarbons containing only simple bonds and forming a homologous series with the general formula CnH2n + 2. ... ... Wikipedia

This article is about chemical compounds. For an article about the Canadian aluminum company Alcan, see linear or branched acyclic hydrocarbons containing only simple bonds and forming a homologous series with the general formula CnH2n + 2. ... ... Wikipedia

This article is about chemical compounds. For an article about the Canadian aluminum company Alcan, see linear or branched acyclic hydrocarbons containing only simple bonds and forming a homologous series with the general formula CnH2n + 2. ... ... Wikipedia

This article is about chemical compounds. For an article about the Canadian aluminum company Alcan, see linear or branched acyclic hydrocarbons containing only simple bonds and forming a homologous series with the general formula CnH2n + 2. ... ... Wikipedia

The names of the first ten members of the saturated hydrocarbon series have already been given. To emphasize that an alkane has an unbranched carbon chain, the word normal (n-) is often added to the name, for example: />

CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -C /> H 2 /> -CH 3 />

n-butane n-heptane />

(normal butane) (normal heptane)

When a hydrogen atom is removed from an alkane molecule, one-year particles are formed, called hydrocarbon radicals (abbreviated with the letter R). The names of monovalent radicals are derived from the names of the corresponding hydrocarbons with the ending -an replaced by -yl. Here are relevant examples:

Radicals are formed not only by organic, but also by inorganic compounds. So, if the hydroxyl group OH is subtracted from nitric acid, then you get a monovalent radical - NO 2, called the nitro group, etc./>

When two hydrogen atoms are removed from a hydrocarbon molecule, bivalent radicals are obtained. Their names are also derived from the names of the corresponding saturated hydrocarbons with the replacement of the ending -an by -ylidene (if the hydrogen atoms are torn off from one carbon atom) or -ylene (if the hydrogen atoms are torn off from two adjacent carbon atoms). The radical CH 2 = has the name methylene ./>

The names of radicals are used in the nomenclature of many hydrocarbon derivatives. For example: CH 3 I /> - methyl iodide, С 4 Н 9 Сl /> - butyl chloride, СН 2 Сl /> 2 /> - methylene chloride, С 2 Н 4 В /> r /> 2 /> - ethylene bromide (if bromine atoms are bonded to different carbon atoms) or ethylidene bromide (if bromine atoms are bonded to one carbon atom) ./>

For the name of isomers, two nomenclatures are widely used: the old - rational and modern - substitutional, which is also called systematic or international (proposed by the International Union of Theoretical and Applied Chemistry IUPAC) ./>

According to the rational nomenclature, hydrocarbons are considered as derivatives of methane, in which one or more hydrogen atoms are replaced by radicals. If in the formula the same radicals are repeated several times, then they are indicated by Greek numerals: di - two, three - three, tetra - four, penta - five, hexa - six, etc. For example:

A rational nomenclature is convenient for not very complex connections ./>

According to the substituent nomenclature, the name is based on one carbon chain, and all other fragments of the molecule are considered as substituents. In this case, the longest chain of carbon atoms is selected and the chain atoms are numbered from the end to which the hydrocarbon radical is closer. Then they call: 1) the number of the carbon atom to which the radical is bound (starting with the simplest radical); 2) hydrocarbon, which corresponds to a long chain. If the formula contains several identical radicals, then before their name indicate the number in words (di-, tri-, tetra-, etc.), and the numbers of the radicals are separated by commas. Here is how hexane isomers should be called according to this nomenclature: />

/>

Here's a more complex example:

Both substitutional and rational nomenclature are used not only for hydrocarbons, but also for other classes of organic compounds. For some organic compounds, historically established (empirical) or so-called trivial names (formic acid, sulfuric ether, urea, etc.) are used.

When writing formulas for isomers, it is easy to notice that carbon atoms occupy different positions in them. A carbon atom that is linked to only one carbon atom in the chain is called primary, with two - secondary, with three - tertiary, with four - quaternary. So, for example, in the last example, carbon atoms 1 and 7 are primary, 4 and 6 are secondary, 2 and 3 are tertiary, 5 is quaternary. The properties of hydrogen atoms, other atoms and functional groups depend on which carbon atom they are associated with: primary, secondary or tertiary. This should always be taken into account ./>

Creams, peels, lotions, milk are usually treated with reverence. After all, in theory, they should give health and beauty to faded skin! Alas, this is not always the case.

The reason is the presence of harmful synthetic surfactants in cosmetic products.

In itself, the presence of surfactants (surfactants) in cosmetic preparations is natural, because they contribute to the penetration of other components into the skin.

But not all surfactants are created equal. Some of them negate the positive properties of the face cream, as they dry out the skin of the face and body and expose it to destruction.

The fact is that they only affect the epidermis (the surface layer of the skin), while the epithelial cells and bacteria necessary for skin renewal inhibit. This is how the normal microflora of the skin is damaged, resulting in aging.

Any woman should be able to recognize her enemies. How? Learn to read the labels carefully, because, among other components, the so-called "harmful" are sometimes indicated there.

Methyl-, propyl-, butyl- and ethyl-parabens

The harmful ones include stabilizers and preservatives. it butyl-, propyl, ethyl- and methyl parabens that are used in many daily care products.

Parabens have a mild estrogenic effect, which means that those for whom estrogen is contraindicated should be treated with caution. First of all, this applies to pregnant women, since excess estrogen can cause abnormalities in the reproductive function of the fetus in expectant mothers.

In addition, according to the latest research, there is a possibility that parabens increase the risk of breast cancer.

Methyl- and propyl parabens cause allergic contact dermatitis.

Propylene glycol

A mixture of petrochemical products propylene glycol contained in many cosmetics, since it promotes the penetration of components into tissues.

There is a lot of writing about propylene glycol, but there is no definite verdict yet. It is believed to be safe for those without skin problems. However, if you are prone to allergies, it can cause eczema and hives.

For those with dry skin, be aware that propylene glycol draws moisture from the stratum corneum in a dry atmosphere. and polyethylene glycol peg, peg)

Diethanolamine, triethanolamine

Foaming agents diethanolamine and triethanolamine contain ammonia. With systematic use, they have a toxic effect, causing eye irritation, allergic reactions, dry skin and hair.

Sodium lauryl sulfate

Lauryl sodium added to cosmetics, especially shampoos, so that the active ingredients better penetrate the skin. However, with prolonged use, it can accumulate in the skin and have a negative effect on the hair follicles. As a result, dandruff appears, the hair dries up, splits. May promote hair loss.

It is completely undesirable to use shampoos and foams with sodium lauril for children: SLS penetrates into the eyes, brain, heart, liver and is retained there in high concentrations.

Manufacturers disguise their products with SLS under the natural innocent phrase "derived from coconuts", but that should alert you.

Petrolatum

Even petrolatum- familiar, old, kind - can harm our skin, since in fact it does not moisturize it - as is commonly believed, but causes dry skin and the appearance of cracks.

The reason lies in the fact that petroleum jelly (like other mineral oils) forms an impenetrable film on the skin - not releasing moisture, but also not allowing it to be received from the outside.

Glycerol

Glycerin is considered a natural skin moisturizer. Unfortunately, this only works if the air humidity is over 65-70%.

In drier rooms, glycerin - instead of taking moisture from the air - extracts moisture from the cells in the deeper layers of the skin. As a result, dry skin becomes even drier.

Bentonite

Bentonite is a natural mineral found in face masks.

Bentonite grains sometimes have sharp edges, which causes micro-scratches on the skin. But worst of all, bentonite dries out the skin. Forming an impenetrable film, it interferes with the natural respiration of the skin and the release of waste products, retains toxins and toxins. All this worsens the condition of the skin.

The question is, is such a face mask needed?

Iazolidinyl urea, imidazo lidinyl urea

Iazolidinyl used as a preservative. It emits formaldehyde, which has a toxic effect on the skin. With a tendency to allergies, it can cause contact dermatitis.

Other names: Germall II and Germall 115 (Germall II, Germall 115).

* * *

If you are going to purchase funds designed to give health and beauty, do not be too lazy to study their composition.

The longer the list of components of a cosmetic product, the more confidence in the manufacturer. Three to five components most likely means that there is a reason not to indicate the composition in full.

It is most reasonable to give preference to cosmetic products that:

• They are white, that is, they contain a minimum of dyes (like Avon products).
• They are odorless. Low fruity, floral, or herbal aromas are allowed if essential oils are included.
• They do not foam at all or hardly.

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