Angle between alkane bonds. Organic chemistry. Alkanes. Physical properties of alkanes

The table shows some representatives of a number of alkanes and their radicals.

Formula	Name	Radical name
		CH3 methyl
		C3H7 cut
		C4H9 butyl
	isobutane	isobutyl
	isopentane	isopentyl
	neopentane	neopentyl
		The table shows that these hydrocarbons differ from each other in the number of groups - CH2 -. Such a series of similar structures, having similar chemical properties and differing from each other in the number of these groups is called a homologous series. And the substances that make it up are called homologues. Homologues - substances similar in structure and properties, but differing in composition by one or more homologous differences (- CH2 -) Carbon chain - zigzag (if n ≥ 3) σ - bonds (free rotation around bonds) length (-C-C-) 0.154 nm binding energy (-C-C-) 348 kJ/mol All carbon atoms in alkane molecules are in a state of sp3 hybridization the angle between the C-C bonds is 109°28", therefore the molecules of normal alkanes with a large number of carbon atoms have a zigzag structure (zigzag). The length of the C-C bond in saturated hydrocarbons is 0.154 nm (1 nm = 1 * 10-9 m). a) electronic and structural formulas; b) spatial structure 4. Isomerism- STRUCTURAL isomerism of the chain with C4 is characteristic One of these isomers ( n-butane) contains an unbranched carbon chain, and the other, isobutane, contains a branched one (isostructure). The carbon atoms in a branched chain differ in the type of connection with other carbon atoms. Thus, a carbon atom bonded to only one other carbon atom is called primary, with two other carbon atoms - secondary, with three - tertiary, with four - quaternary. With an increase in the number of carbon atoms in the molecules, the possibilities for chain branching increase, i.e. the number of isomers increases with the number of carbon atoms. Comparative characteristics of homologues and isomers 1. They have their own nomenclature radicals(hydrocarbon radicals) Alkane WITHnH2n+2 Radical(R) WITHnH2n+1 NAME Physical properties Under normal conditions C1-C4 - gases C5-C15 - liquid C16 - solid The melting and boiling points of alkanes and their densities increase in the homologous series with increasing molecular weight. All alkanes are lighter than water and are insoluble in it, but they are soluble in non-polar solvents (for example, benzene) and are themselves good solvents. The physical properties of some alkanes are presented in the table. Table 2. Physical properties of some alkanes a) Halogenation under the influence of light - hν or heating (stagewise - the replacement of hydrogen atoms with halogen has a sequential chain character. A great contribution to the development of chain reactions was made by physicist, academician, Nobel Prize laureate N. N. Semenov) The reaction produces haloalkanes RG or with n H 2 n +1 G (G- these are halogens F, Cl, Br, I) CH4 + Cl2 hν → CH3Cl + HCl (1st stage); methane chloromethane CH3Cl + Cl2 hν → CH2Cl2 + HCl (2nd stage); dichloromethane СH2Cl2 + Cl2 hν → CHCl3 + HCl (3rd stage); trichloromethane CHCl3 + Cl2 hν → CCl4 + HCl (4th stage). carbon tetrachloride The rate of the reaction of replacing hydrogen with a halogen atom in haloalkanes is higher than that of the corresponding alkane, this is due to the mutual influence of the atoms in the molecule: Electron bond density C- Cl is shifted towards the more electronegative chlorine, as a result a partial negative charge accumulates on it, and a partial positive charge accumulates on the carbon atom. The carbon atom in the methyl group (- CH3) experiences a deficit of electron density, so it compensates for its charge at the expense of neighboring hydrogen atoms, as a result the C-H bond becomes less strong and hydrogen atoms are more easily replaced by chlorine atoms. As the hydrocarbon radical increases, the most mobile hydrogen atoms remain at the carbon atom closest to the substituent: CH3 - CH2 - Cl + Cl2 hν → CH3 - CHCl2 + HCl chloroethane 1 ,1-dichloroethane With fluorine, the reaction occurs explosively. With chlorine and bromine an initiator is required. Iodination is reversible, so an oxidizing agent is required to removeHIfrom the rector's office. Attention! In alkane substitution reactions, hydrogen atoms are most easily replaced at tertiary carbon atoms, then at secondary carbon atoms, and, lastly, at primary carbon atoms. For chlorination, this pattern is not observed whenT>400˚C. b) Nitration (reaction of M.I. Konovalov, he carried it out for the first time in 1888) CH4 + HNO3 (solution) t˚WITH → CH3NO2 + H2O nitromethane RNO2 or WITH n H2n+1 NO2 ( nitroalkane )

It would be useful to start with a definition of the concept of alkanes. These are saturated or saturated. We can also say that these are carbons in which the connection of C atoms is carried out through simple bonds. The general formula is: CnH₂n+ 2.

It is known that the ratio of the number of H and C atoms in their molecules is maximum when compared with other classes. Due to the fact that all valences are occupied by either C or H, the chemical properties of alkanes are not clearly expressed, so their second name is the phrase saturated or saturated hydrocarbons.

There is also an older name that best reflects their relative chemical inertness - paraffins, which means “devoid of affinity.”

So, the topic of our conversation today is: “Alkanes: homological series, nomenclature, structure, isomerism.” Data regarding their physical properties will also be presented.

Alkanes: structure, nomenclature

In them, the C atoms are in a state called sp3 hybridization. In this regard, the alkane molecule can be demonstrated as a set of tetrahedral C structures that are connected not only to each other, but also to H.

Between the C and H atoms there are strong, very low-polar s-bonds. Atoms always rotate around simple bonds, which is why alkane molecules take on various shapes, and the bond length and the angle between them are constant values. Shapes that transform into each other due to the rotation of the molecule around σ bonds are usually called conformations.

In the process of abstraction of an H atom from the molecule in question, 1-valent species called hydrocarbon radicals are formed. They appear as a result of not only but also inorganic compounds. If you subtract 2 hydrogen atoms from a saturated hydrocarbon molecule, you get 2-valent radicals.

Thus, the nomenclature of alkanes can be:

• radial (old version);
• substitution (international, systematic). It was proposed by IUPAC.

Features of radial nomenclature

In the first case, the nomenclature of alkanes is characterized as follows:

1. Consideration of hydrocarbons as derivatives of methane, in which 1 or several H atoms are replaced by radicals.
2. High degree of convenience in the case of not very complex connections.

Features of substitution nomenclature

The substitutive nomenclature of alkanes has the following features:

1. The basis for the name is 1 carbon chain, while the remaining molecular fragments are considered as substituents.
2. If there are several identical radicals, the number is indicated before their name (strictly in words), and the radical numbers are separated by commas.

Chemistry: nomenclature of alkanes

For convenience, the information is presented in table form.

Substance name	The basis of the name (root)	Molecular formula	Name of carbon substituent	Carbon Substituent Formula

The above nomenclature of alkanes includes names that have developed historically (the first 4 members of the series of saturated hydrocarbons).

The names of unexpanded alkanes with 5 or more C atoms are derived from Greek numerals that reflect the given number of C atoms. Thus, the suffix -an indicates that the substance is from a series of saturated compounds.

When composing the names of unfolded alkanes, the main chain is the one that contains the maximum number of C atoms. It is numbered so that the substituents have the lowest number. In the case of two or more chains of the same length, the main one becomes the one that contains the largest number of substituents.

Isomerism of alkanes

The parent hydrocarbon of their series is methane CH₄. With each subsequent representative of the methane series, a difference from the previous one is observed in the methylene group - CH₂. This pattern can be traced throughout the entire series of alkanes.

The German scientist Schiel put forward a proposal to call this series homological. Translated from Greek it means “similar, similar.”

Thus, a homologous series is a set of related organic compounds that have the same structure and similar chemical properties. Homologues are members of a given series. Homologous difference is a methylene group in which 2 neighboring homologues differ.

As mentioned earlier, the composition of any saturated hydrocarbon can be expressed using the general formula CnH₂n + 2. Thus, the next member of the homologous series after methane is ethane - C₂H₆. To convert its structure from methane, it is necessary to replace 1 H atom with CH₃ (figure below).

The structure of each subsequent homolog can be deduced from the previous one in the same way. As a result, propane is formed from ethane - C₃H₈.

What are isomers?

These are substances that have an identical qualitative and quantitative molecular composition (identical molecular formula), but a different chemical structure, and also have different chemical properties.

The hydrocarbons discussed above differ in such a parameter as boiling point: -0.5° - butane, -10° - isobutane. This type of isomerism is called carbon skeleton isomerism; it belongs to the structural type.

The number of structural isomers increases rapidly as the number of carbon atoms increases. Thus, C₁₀H₂₂ will correspond to 75 isomers (not including spatial ones), and for C₁₅H₃₂ 4347 isomers are already known, for C₂₀H₄₂ - 366,319.

So, it has already become clear what alkanes are, homologous series, isomerism, nomenclature. Now it’s worth moving on to the rules for compiling names according to IUPAC.

IUPAC nomenclature: rules for the formation of names

First, it is necessary to find in the hydrocarbon structure the carbon chain that is longest and contains the maximum number of substituents. Then you need to number the C atoms of the chain, starting from the end to which the substituent is closest.

Secondly, the base is the name of an unbranched saturated hydrocarbon, which, in terms of the number of C atoms, corresponds to the main chain.

Thirdly, before the base it is necessary to indicate the numbers of the locants near which the substituents are located. The names of the substituents are written after them with a hyphen.

Fourthly, in the case of the presence of identical substituents at different C atoms, the locants are combined, and a multiplying prefix appears before the name: di - for two identical substituents, three - for three, tetra - four, penta - for five, etc. Numbers must be separated from each other by a comma, and from words by a hyphen.

If the same C atom contains two substituents at once, the locant is also written twice.

According to these rules, the international nomenclature of alkanes is formed.

Newman projections

This American scientist proposed special projection formulas for graphical demonstration of conformations - Newman projections. They correspond to forms A and B and are presented in the figure below.

In the first case, this is an A-occluded conformation, and in the second, it is a B-inhibited conformation. In position A, the H atoms are located at a minimum distance from each other. This form corresponds to the highest energy value, due to the fact that the repulsion between them is greatest. This is an energetically unfavorable state, as a result of which the molecule tends to leave it and move to a more stable position B. Here the H atoms are as far apart as possible from each other. Thus, the energy difference between these positions is 12 kJ/mol, due to which the free rotation around the axis in the ethane molecule, which connects the methyl groups, is uneven. After entering an energetically favorable position, the molecule lingers there, in other words, “slows down.” That is why it is called inhibited. The result is that 10 thousand ethane molecules are in the inhibited form of conformation at room temperature. Only one has a different shape - obscured.

Obtaining saturated hydrocarbons

From the article it has already become known that these are alkanes (their structure and nomenclature were described in detail earlier). It would be useful to consider ways to obtain them. They are released from natural sources such as oil, natural, and coal. Synthetic methods are also used. For example, H₂ 2H₂:

1. Hydrogenation process CnH₂n (alkenes)→ CnH₂n+2 (alkanes)← CnH₂n-2 (alkynes).
2. From a mixture of C and H monoxide - synthesis gas: nCO+(2n+1)H₂→ CnH₂n+2+nH₂O.
3. From carboxylic acids (their salts): electrolysis at the anode, at the cathode:

• Kolbe electrolysis: 2RCOONa+2H₂O→R-R+2CO₂+H₂+2NaOH;
• Dumas reaction (alloy with alkali): CH₃COONa+NaOH (t)→CH₄+Na₂CO₃.

1. Oil cracking: CnH₂n+2 (450-700°)→ CmH₂m+2+ Cn-mH₂(n-m).
2. Gasification of fuel (solid): C+2H₂→CH₄.
3. Synthesis of complex alkanes (halogen derivatives) that have fewer C atoms: 2CH₃Cl (chloromethane) +2Na →CH₃- CH₃ (ethane) +2NaCl.
4. Decomposition of methanides (metal carbides) by water: Al₄C₃+12H₂O→4Al(OH₃)↓+3CH₄.

Physical properties of saturated hydrocarbons

For convenience, the data is grouped into a table.

Formula	Alkane	Melting point in °C	Boiling point in °C	Density, g/ml
				0.415 at t = -165°С
				0.561 at t= -100°C
				0.583 at t = -45°C
				0.579 at t =0°C
	2-Methylpropane			0.557 at t = -25°C
	2,2-Dimethylpropane
	2-Methylbutane
	2-Methylpentane
	2,2,3,3-Tetra-methylbutane
	2,2,4-Trimethylpentane
n-C₁₀H₂₂
n-C₁₁H₂₄	n-Undecane
n-C₁₂H₂₆	n-Dodecane
n-C₁₃H₂₈	n-Tridecan
n-C₁₄H₃₀	n-Tetradecane
n-C₁₅H₃₂	n-Pentadecan
n-C₁₆H₃₄	n-Hexadecane
n-C₂₀H₄₂	n-Eicosane
n-C₃₀H₆₂	n-Triacontan		1 mmHg st
n-C₄₀H₈₂	n-Tetracontane		3 mmHg Art.
n-C₅₀H₁₀₂	n-Pentacontan		15 mmHg Art.
n-C₆₀H₁₂₂	n-Hexacontane
n-C₇₀H₁₄₂	n-Heptacontane
n-C₁₀₀H₂₀₂

Conclusion

The article examined such a concept as alkanes (structure, nomenclature, isomerism, homologous series, etc.). A little is said about the features of radial and substitutive nomenclatures. Methods for obtaining alkanes are described.

In addition, the article lists in detail the entire nomenclature of alkanes (the test can help you assimilate the information received).

Alkanes- saturated (saturated) hydrocarbons. A representative of this class is methane ( CH 4). All subsequent saturated hydrocarbons differ by CH 2- a group that is called a homologous group, and compounds are called homologues.

General formula - WITHnH 2 n +2 .

Structure of alkanes.

Each carbon atom is in sp 3- hybridization, forms 4 σ - communications (1 S-S and 3 S-N). The shape of the molecule is in the form of a tetrahedron with an angle of 109.5°.

The bond is formed through the overlap of hybrid orbitals, with the maximum area of ​​overlap lying in space on the straight line connecting the atomic nuclei. This is the most efficient overlap, so the σ bond is considered the strongest.

Isomerism of alkanes.

For alkanes isomerism of the carbon skeleton is characteristic. Limit connections can take on different geometric shapes while maintaining the angle between the connections. For example,

The different positions of the carbon chain are called conformations. Under normal conditions, the conformations of alkanes freely transform into each other through the rotation of C-C bonds, which is why they are often called rotary isomers. There are 2 main conformations - “inhibited” and “eclipsed”:

Isomerism of the carbon skeleton of alkanes.

The number of isomers increases with increasing carbon chain growth. For example, butane has 2 isomers:

For pentane - 3, for heptane - 9, etc.

If a molecule alkane subtract one proton (hydrogen atom), you get a radical:

Physical properties of alkanes.

Under normal conditions - C 1 -C 4- gases , From 5 to From 17- liquids, and hydrocarbons with more than 18 carbon atoms - solids.

As the chain grows, the boiling and melting points increase. Branched alkanes have lower boiling points than normal ones.

Alkanes insoluble in water, but soluble in non-polar organic solvents. Mix easily with each other.

Preparation of alkanes.

Synthetic methods for producing alkanes:

1. From unsaturated hydrocarbons - the “hydrogenation” reaction occurs under the influence of a catalyst (nickel, platinum) and at a temperature:

2. From halogen derivatives - Wurtz reaction: the interaction of monohaloalkanes with sodium metal, resulting in alkanes with double the number of carbon atoms in the chain:

3. From salts of carboxylic acids. When a salt reacts with an alkali, alkanes are obtained that contain 1 less carbon atom compared to the original carboxylic acid:

4. Production of methane. In an electric arc in a hydrogen atmosphere:

C + 2H 2 = CH 4.

In the laboratory, methane is obtained as follows:

Al 4 C 3 + 12H 2 O = 3CH 4 + 4Al(OH) 3.

Chemical properties of alkanes.

Under normal conditions, alkanes are chemically inert compounds; they do not react with concentrated sulfuric and nitric acid, with concentrated alkali, or with potassium permanganate.

Stability is explained by the strength of the bonds and their non-polarity.

Compounds are not prone to bond breaking reactions (addition reactions); they are characterized by substitution.

1. Halogenation of alkanes. Under the influence of a light quantum, radical substitution (chlorination) of the alkane begins. General scheme:

The reaction follows a chain mechanism, in which there are:

A) Initiating the circuit:

B) Chain growth:

B) Open circuit:

In total it can be presented as:

2. Nitration (Konovalov reaction) of alkanes. The reaction occurs at 140 °C:

The reaction proceeds most easily with the tertiary carbon atom than with the primary and secondary ones.

3. Isomerization of alkanes. Under specific conditions, alkanes of normal structure can transform into branched ones:

4. Cracking alkane. Under the action of high temperatures and catalysts, higher alkanes can break their bonds, forming alkenes and lower alkanes:

5. Oxidation of alkanes. Under different conditions and with different catalysts, alkane oxidation can lead to the formation of alcohol, aldehyde (ketone) and acetic acid. Under conditions of complete oxidation, the reaction proceeds to completion - until water and carbon dioxide are formed:

Application of alkanes.

Alkanes have found wide application in industry, in the synthesis of oil, fuel, etc.

The content of the article

ALKANES AND CYCLOALKANES– hydrocarbons in which all carbon atoms are connected to each other and to hydrogen atoms by simple (single) bonds. Alkanes (synonyms - saturated hydrocarbons, saturated hydrocarbons, paraffins) - hydrocarbons with the general formula C n H 2 n+2 , where n– number of carbon atoms. The familiar polyethylene has the same formula, only the size n it is very large and can reach tens of thousands. In addition, polyethylene contains molecules of different lengths. In cycloalkanes, the carbon atoms form a closed chain; if there is one cycle, the formula of the cycloalkane is C n H 2 n .

Depending on the order of connection of carbon atoms in a chain, alkanes are divided into linear and branched. Accordingly, for alkanes with nі 4 it is possible that there is more than one substance with the same formula. Such substances are called isomers (from the Greek. isis– equal, identical and meros – share, part.

Names of alkanes.

The word "alkane" is of the same origin as "alcohol" ( see below). The obsolete term "paraffin" comes from the Latin parum - little, insignificantly and affinis - related; paraffins have low reactivity with respect to most chemical reagents. Many paraffins are homologues; in the homologous series of alkanes, each subsequent member differs from the previous one by one methylene group CH 2. The term comes from the Greek homologos - corresponding, similar.

Nomenclature (from lat. nomenclature– list of names) the names of alkanes are constructed according to certain rules, which are not always unambiguous. So, if there are various substituents in an alkane molecule, then in the name of the alkane they are listed in alphabetical order. However, this order may vary in different languages. For example, the hydrocarbon CH 3 –CH(CH 3)–CH(C 2 H 5)–CH 2 –CH 2 –CH 3 in accordance with this rule will be called 2-methyl-3-ethylhexane in Russian, and in English 3-ethyl-2-methylhexane…

In accordance with the name of the hydrocarbon, alkyl radicals are also called: methyl (CH 3 -), ethyl (C 2 H 5 -), isopropyl (CH 3) 2 CH-, tues-butyl C 2 H 5 –CH (CH 3)-, rubs-butyl (CH 3) 3 C-, etc. Alkyl radicals are included as a whole in the composition of many organic compounds; in the free state, these particles with an unpaired electron are extremely active.

Some isomers of alkanes also have trivial names ( cm. TRIVIAL SUBSTANCE NAMES, e.g. isobutane (2-methylpropane), isooctane (2,2,4-trimethylpentane), neopentane (2,3-dimethylpropane), squalane (2,6,10,15,19,23-hexamethyltetracosane) , whose name comes from the Latin squalus– shark (an unsaturated derivative of squalane – squalene, a compound important for metabolism, was first discovered in the liver of a shark). The trivial name for the pentyl radical (C 5 H 11) is amyl. It comes from the Greek. amylon– starch: once upon a time, isoamyl alcohol C 5 H 11 OH (3-methylbutanol-1) was called “amyl alcohol of fermentation”, since it forms the basis of fusel oil, and it is formed as a result of the fermentation of sugary substances - products of starch hydrolysis.

The simplest member of the cycloalkane series C n H 2 n– cyclopropane ( n= 3). Its homologues are called the same as alkanes with the addition of the prefix “cyclo” (cyclobutane, cyclopentane, etc.). In cycloalkanes, isomerism is possible due to the presence of side alkyl groups and their location in the ring. For example, cyclohexane, methylcyclopentane, 1,1-, 1,2- and 1,3-dimethylcyclobutanes, 1,1,2- and 1,2,3-trimethylcyclopropanes are isomeric.

The number of alkane isomers increases sharply with increasing number of carbon atoms. The names of some alkanes, as well as the theoretical number of their possible isomers, are given in the table.

Table: Theoretical number of possible isomers of alkanes

Formula	Name	Number of isomers	Formula	Name	Number of isomers
CH 4	Methane	1	C 11 N 24	Undekan	159
C 2 H 6	Ethane	1	C 12 N 26	Dodecan	355
C 3 H 8	Propane	1	C 13 N 28	Tridecan	802
C 4 H 10	Butane	2	C 14 N 30	Tetradecane	1858
C 5 H 12	Pentane	3	C 15 N 32	Pentadecane	4347
C 6 H 14	Hexane	5	C 20 N 42	Eikosan	366319
C 7 H 16	Heptane	9	C 25 N 52	Pentacosan	36797588
C 8 H 18	Octane	18	C 30 N 62	Triacontan	4111846763
C 9 H 20	Nonan	35	C 40 N 82	Tetracontan	62481801147341
C 10 H 22	Dean	75	C 100 N 202	Hectane	about 5.921 10 39

Understanding most of the nomenclature names of saturated hydrocarbons is not very difficult even for those who did not study Greek in a classical gymnasium. These names come from Greek numerals with the addition of the suffix -an. It is more difficult with the first members of the series: they do not use numerals, but other Greek roots associated with the names of the corresponding alcohols or acids. These alcohols and acids were known long before the discovery of the corresponding alkanes; an example is ethyl alcohol and ethane (obtained only in 1848).

Methane (as well as methanol, methyl, methylene, etc.) have a common root “met”, which in chemistry denotes a group containing one carbon atom: methyl CH 3, methylene (methylidene) CH 2, methine (methylidine) CH. Historically, the first such substance was methyl (also known as wood) alcohol, methanol, which was previously obtained by dry distillation of wood. Its name comes from the Greek words methy - to intoxicate wine and hile - forest (so to speak, “wood wine”). The most amazing thing here is that methane, amethyst and honey have a common root! In ancient times, precious stones were endowed with magical properties (and many still believe in this). Thus, it was believed that beautiful purple stones protected against intoxication, especially if a drinking cup was made from this stone. Together with the negative prefix it turned out amethystos - counteracting intoxication. The word honey, it turns out, is present in almost all European languages: English. mead - honey (as a drink), German Met (in Old German metu), Dutch mede, Swedish mjöd, Danish mjød, Lithuanian and Latvian medus, not to mention the Slavic languages. All these words, including the Greek, come from the Indo-European medhu, meaning sweet drink. The Greek brandy Metaxa is not far behind them, although it is not at all sweet.

Ethane (as well as ether, ethanol, alcohol, alkane) have a common origin. Ancient Greek philosophers used the word aither to describe a certain substance that permeates the cosmos. When alchemists in the 8th century. They obtained an easily evaporating liquid from wine alcohol and sulfuric acid, it was called sulfuric ether. In the 19th century found out that sulfuric ether (in English ether) belongs to the so-called ethers and contains a group of two carbon atoms - the same as ethyl alcohol (ethanol); this group was called ethyl. Thus, the name of the substance “ethyl ether” (C 2 H 5 –O–C 2 H 5) is essentially “oil oil”.

The name ethane comes from “ethyl”. One of the names for ethanol, alcohol, is of the same origin as the word alkane (also alkene, alkyne, alkyl). In Arabic, al-kohl means powder, powder, dust. At the slightest breath they rise into the air, just like wine vapors - the “alcohol of wine”, which over time simply turned into alcohol.

Why is there a “t” in “ethane” and “ethanol”, and “f” in “ether”? After all, in English, unlike Russian, the words “ether” and “ethyl” have similar spellings and sounds. The combination th goes back to the Greek letter q (theta); in the Russian language until 1918, the letter “fita” had the same style, which, however, was pronounced as “f” and was used for the sole purpose of distinguishing words in which this letter comes from the Greek q and 247 (“fi”). In Western European languages, Greek. j went to ph, and q to th. In the Russian language, many words contain “fita” back in the 18th century. was replaced by the letter “f”: theater instead of “qeaftr”, mathematics instead of “maqematics”, theory instead of “qeory”... In this regard, it is interesting that in Dahl’s dictionary, published in 1882, it is written eqir, and in the encyclopedic dictionary of Brockhaus and Efron (1904) – “ether”.

By the way, esters in Western languages ​​are ester, not ether. But the word “ester” does not exist in the Russian language, so any chemist’s eyes are hurt by the illiterate translation of the English polyester on the labels of textile products as “polyester” instead of “polyester”, “polyester fiber” (polyesters include, for example, lavsan, terylene, dacron).

The names “propane” and “butane” come from the names of the corresponding acids – propionic and butanoic (butyric). Propionic acid is the “first” (i.e. shortest chain) found in fats ( cm. FATS AND OILS), and its name is derived from the Greek. protos- first and pion– fat. Butane and butanoic acid butyric acid) – from Greek. butyron- oil; In Russian, butyrates are salts and esters of butyric acid. This acid is released when the oil goes rancid.

Further, starting with pentane, the names are derived from Greek numerals. A rare exception is cetane, one of the names for C16 hexadecane. This word comes from the name cetyl alcohol, which was obtained in 1823 by the French chemist Michel Eugene Chevreul. Chevreul isolated this substance from spermaceti, a waxy substance from the head of the sperm whale. The word spermaceti comes from the Greek sperma - seed and ketos - large sea animal (whale, dolphin). From the Latin spelling of the second word (cetus) comes cetyl alcohol C 16 H 33 OH (hexadecanol) and cetane.

In the Russian language there are many words with the same roots as alkanes: Pentagon, heptachord (sound scale of 7 steps), dodecaphony (method of musical composition), octave, decima and undecima (musical intervals), octet and nonet (ensembles of 8 and 9 musicians), pentode, hexode and heptode (radio tubes); hexameter (poetic meter), octahedron, decade, decan, hectare, October, December, etc. and so on.

The alkane with the longest molecules was synthesized by English chemists in 1985. This is nonacontatrictan C 390 H 782, containing a chain of 390 carbon atoms. The researchers were interested in how such long chains would pack during crystallization (flexible hydrocarbon chains can fold easily).

Number of isomers of alkanes.

The problem of the theoretically possible number of isomers of alkanes was first solved by the English mathematician Arthur Cayley (1821–1895), one of the founders of an important branch of mathematics - topology (in 1879 he published the first article on the famous “problem of four colors”: are there enough of them to color any geographical cards; this problem was solved only in 1976). It turned out that there is no formula by which one can use the number of carbon atoms in a C alkane n H 2 n+2 calculate the number of its isomers. There are only so-called recurrent formulas (from the Latin recurrences– returning), which allow you to calculate the number of isomers n th member of the series, if the number of isomers of the previous member is already known. Therefore, calculations for large n were obtained relatively recently using computers and reduced to hydrocarbon C 400 H 802; for it, taking into account spatial isomers, a value was obtained that is difficult to imagine: 4.776·10 199. And starting from the alkane C 167 H 336, the number of isomers exceeds the number of elementary particles in the visible part of the Universe, which is estimated as 10 80. The number of isomers indicated in the table for most alkanes will increase significantly if we also consider mirror-symmetrical molecules - stereoisomers ( cm. OPTICAL ISOMERISM): for heptane - from 9 to 11, for decane - from 75 to 136, for eicosane - from 366,319 to 3,396,844, for hectane - from 5.921 10 39 to 1.373 10 46, etc.

From the point of view of a chemist, the number of structural isomers of saturated hydrocarbons is of practical interest only for the first members of the series. Even for a relatively simple alkane containing only one and a half dozen carbon atoms, the overwhelming number of isomers have not been obtained and are unlikely to ever be synthesized. For example, the last of the theoretically possible 75 isomers of decane were synthesized only in 1968. And this was done for practical purposes - to have a more complete set of standard compounds by which various hydrocarbons, for example, those found in oil, can be identified. By the way, all 18 possible octane isomers have been found in various types of oil.

But the most interesting thing is that, starting with heptadecane C 17 H 36, at first only some of the theoretically possible number of isomers, then many, and finally almost all are a striking example of “paper chemistry”, i.e. cannot exist in reality. The fact is that as the number of carbon atoms in the molecules of branched isomers increases, serious problems of spatial packing arise. After all, mathematicians treated carbon and hydrogen atoms as points, when in fact they have a finite radius. Thus, a methane “ball” has 4 hydrogen atoms on its “surface”, which are freely placed on it. In neopentane C(CH 3) 4 there are already 12 hydrogen atoms on the “surface”, located much closer to each other; but there is still room for them to be placed. But for alkane 4 (C 17 H 36), there is not enough space on the surface to accommodate all 36 hydrogen atoms in 12 methyl groups; This is easy to check if you draw a flat image (or, even better, make a three-dimensional model from plasticine and matches) for similar isomers, maintaining the constancy of the C–C and C–H bond lengths and all angles between them). With growth n placement problems also arise for carbon atoms. As a result, despite the fact that the number of possible isomers with increasing n increases very quickly, the share of “paper” isomers grows much faster. A computer-based assessment showed that as n the ratio of the number of truly possible isomers to the number of “paper” ones quickly approaches zero. That is why the calculation of the exact number of isomers of saturated hydrocarbons for large n, which once aroused considerable interest, now has only theoretical significance for chemists.

Structure and physical properties of alkanes.

Alkanes have four sp 3 hybrid orbitals of the carbon atom ( cm. ORBITALS) are directed towards the vertices of the tetrahedron with an angle between them of about 109°28" - it is in this case that the repulsion between electrons and the energy of the system are minimal. As a result of the overlap of these orbitals with each other, as well as with s-orbitals of hydrogen atoms form s-bonds C–C and C–H. These bonds in alkane molecules are covalent non-polar or low-polar.

Alkanes are divided into primary carbon atoms (they are bonded to only one neighboring C atom), secondary (bonded to two C atoms), tertiary (bonded to three C atoms) and quaternary (bonded to four C atoms). Thus, in 2,2-dimethyl-3-methylpentane CH 3 –C(CH 3) 2 –CH(CH 3) – CH 2 –CH 3 there is one quaternary, one tertiary, one secondary and five primary carbon atoms. The different environments of carbon atoms greatly affect the reactivity of the hydrogen atoms associated with them.

The spatial arrangement of sp 3 orbitals leads, starting from propane, to a zigzag configuration of carbon chains. In this case, rotation of molecular fragments around C–C bonds is possible (in an ethane molecule at 20 ° C - at a speed of millions of revolutions per second!), which makes the molecules of higher alkanes flexible. Straightening of such chains occurs, for example, when stretching polyethylene, which consists of a mixture of alkanes with long chains. Alkane molecules interact weakly with each other, therefore alkanes melt and boil at much lower temperatures than similar substances with polar molecules. The first 4 members of the homologous series of methane are gases under normal conditions; propane and butane are easily liquefied under low pressure (a liquid propane-butane mixture is contained in household gas cylinders). Higher homologues are liquids with the smell of gasoline or solids that are insoluble in water and float on its surface. The melting and boiling points of alkanes increase with increasing number of carbon atoms in the molecule, while the temperature increase gradually slows down, for example, C 100 H 202 melts at 115 ° C, C 150 H 302 - at 123 ° C. Melting and boiling points for the first 25 alkanes are given in the table - it is clear that starting from octadecane, alkanes are solids.

Table: Melting and boiling points of alkanes

Table. MELTING AND BOILING TEMPERATURES OF ALKANES
Alkane	T pl	T bale
Methane	–182,5	–161,5
Ethane	–183,3	–88,6
Propane	–187,7	–42,1
Butane	–138,4	–0,5
Pentane	–129,7	36,1
Hexane	–95,3	68,7
Heptane	–90,6	98,4
Octane	–56,8	125,7
Nonan	–51,0	150,8
Dean	–29,7	174,1
Undekan	–25,6	195,9
Dodecan	–9,6	216,3
Tridecan	–5,5	235,4
Tetradecane	+5,9	253,7
Pentadecane	+9,9	270,6
Hexadecane	18,2	286,8
Heptadecane	22,0	301,9
Octadecan	28,2	316,1
Nonadecane	32,1	329,7
Eikosan	36,8	342,7
Geneikozan	40,5	356,5
Docozan	44,4	368,6
Tricozan	47,6	378,3
Tetracosane	50,9	389,2
Pentacosan	53,7	399,7

The presence of a branch in the chain dramatically changes the physical properties, especially the melting point. So, if hexane has a normal structure ( n-hexane) melts at –95.3° C, then its isomeric 2-methylpentane melts at –153.7° C. This is due to the difficulty of packing branched molecules during their crystallization. As a result, alkanes with chain branches do not crystallize upon rapid cooling, but transform into the glassy state of a supercooled liquid ( cm. GLASS). For example, if a thin ampoule of pentane is immersed in liquid nitrogen (temperature -196 ° C), the substance will turn into a white snow-like mass, while isopentane (2-methylbutane) solidifies into a transparent “glass”.

An original method of separating them is based on the difference in geometric shape of linear and branched alkanes: urea crystals have channels in which straight-chain alkanes can fit, but branched ones cannot.

Cycloalkanes with n= 2, 3 – gases, higher – liquids or solids. The largest cycle that chemists have been able to synthesize is cyclooctaoctacontadictane C 288 H 576. The different shapes of cycloalkane molecules with even and odd numbers of carbon atoms in the molecule lead to a strong even-odd effect regarding the melting point, as can be seen from the table. This effect is explained by the difference in the “convenience” of packing molecules of different shapes in a crystal: the more compact the packing, the stronger the crystal and the higher its melting point. For example, cyclododecane melts almost 70° higher than its closest homologue, cycloundecane. Of course, the mass of the molecule also matters: light molecules melt at a lower temperature.

C 3 H 6	–127,5
C 4 H 8	–50
C 5 H 10	–93,9
C 6 H 12	+6,5
C 7 H 14	–12
C 8 H 16	14,3
S 9 H 18	9,7
C 10 N 20	10,8
C 11 N 22	–7,2
C 12 H 24	61,6
C 13 N 26	23,5
C 14 N 28	54
C 15 N 30	62,1

The ease of rotation around the C–C bond leads to the fact that the molecules of cycloalkanes are not planar (with the exception of cyclopropane), in this way they avoid strong distortion of bond angles. Thus, in cyclohexane and its higher homologues the bond angles are relaxed and close to tetrahedral (109°), while in a hexagon the angles are 120°, in an octagon - 135°, etc. Individual carbon atoms in such cycloalkanes do not occupy a rigidly fixed position: the ring seems to be in constant wave-like motion. Thus, a cyclohexane molecule can be in the form of different geometric structures (conformers) that can transform into each other (cycle inversion). Due to their external similarity, they were called “bathtub” and “chair” (in English literature, a “bathtub” is called a “boat”):

The shape of the chair is more stable; At ordinary temperatures, 99.9% of cyclohexane exists in the more stable chair form. The transition between two forms occurs through an intermediate “twist conformation” (from the English. twist– twist).

In cyclopropane, the angle decreases from 108° to 60°, resulting in high tension and "bent" bonds that are intermediate between normal s- and p-bonds; Due to their shape, these bonds are called “banana” bonds. In this case, the sp 3 orbitals of the carbon atoms overlap only partially. The result is duality in the chemical properties of cyclopropane. On the one hand, substitution of hydrogen atoms is possible in it (a reaction typical of alkanes), on the other hand, addition with ring opening is possible (reaction typical of alkenes, for example: cyclo-C 3 H 6 + Br 2 ® BrCH 2 CH 2 CH 2 Br).

Cycloalkanes with two rings and one common carbon atom are called spiroalkanes. If there are more than two common carbon atoms, then bicycloalkanes, tricycloalkanes, etc. are formed. As a result of such “cross-linking” of several cycles at once, chemists managed to obtain hydrocarbons, the spatial structure of which corresponds to various polyhedra: tetrahedron, cube, prism, etc. Bicyclic derivatives cyclohexane are found in essential oils, coniferous resin, and turpentine. A cycle of six and five carbon atoms is found in camphor, cholesterol, saccharin, piperine (it gives the hot taste to black pepper), nitrogenous bases - nucleotides, and other compounds (some carbon atoms in the cycles can be connected by double bonds, and some are substituted other atoms, such as in saccharin). A cycle of 17 carbon atoms (two of them connected by a double bond) is contained in civeton, an odorous substance, a component of musk, which is used in perfumery. The beautiful adamantane molecule contains three six-membered rings and its structure corresponds to the crystal lattice of diamond. The adamantane structure is found in the antiviral drug rimantadine, in hexamethylenetetramine (in the latter compound, 4 carbon atoms are replaced by nitrogen atoms, which are connected to each other by methylene bridges – CH 2 –). Below are the structures of some cycloalkanes, the molecules of which have more than one differently connected ring.

Bicyclodecane (tetrahydronaphthalene, decalin)

Adamantane

Chemical properties of alkanes.

Alkanes are the least chemically active organic compounds. All C–C and C–H bonds in alkanes are single, so alkanes are incapable of addition reactions. Alkanes are characterized by reactions of replacement of hydrogen atoms with other atoms and groups of atoms. Thus, when methane is chlorinated, methyl chloride CH 3 Cl, methylene chloride CH 2 Cl 2, trichloromethane (chloroform) CHCl 3 and carbon tetrachloride (carbon tetrachloride) CCl 4 are formed. These reactions follow a chain mechanism with the intermediate formation of free radicals.

When chlorinating alkanes, starting with propane, the very first chlorine atom can replace various hydrogen atoms. The direction of substitution depends on the strength of the C–H bond: the weaker it is, the faster the substitution of this particular atom. Primary C–H bonds are usually stronger than secondary ones, and secondary ones are stronger than tertiary ones. As a result, chlorination at 25° C along the secondary bond (CH 3) 2 CH–H occurs 4.5 times faster than through the primary bond C 2 H 5 –H, and the tertiary bond (CH 3) 3 C–H – at 6.7 times faster. The different reactivity of primary, secondary and tertiary hydrogen atoms can result in only one of several possible chlorination products being predominant. For example, when 2,3-dimethylbutane is chlorinated in a solution of carbon disulfide (CS 2), 95% of the 2-chloro derivative and only 5% of the 1-chloro derivative are formed, i.e. 19 times less. If we take into account that in the original alkane there are 6 times more primary hydrogen atoms than tertiary ones, then the ratio of their reactivity will be even greater (19 ґ 6 = 114). Carbon disulfide as a solvent reduces the reactivity of chlorine atoms and accordingly increases its selectivity. Lowering the temperature works the same way.

Bromine atoms are less active; The noticeable activation energy of this reaction leads to the fact that the bromination of alkanes, although it occurs by a chain mechanism, is much slower than chlorination, and only at elevated temperatures or in the light. The lower activity of bromine atoms also leads to increased selectivity of bromination. Thus, if the relative rate of photochemical bromination of ethane at 40°C is taken equal to 1, then the rate of bromination of propane (at the secondary H atom) will be already 220 under the same conditions, and the rate of bromination of isobutane (at the tertiary H atom) will be 19,000

Iodine atoms are the least active, therefore the reaction of iodination of alkanes RH + I 2 ® RI + HI is endothermic, possible only at high temperatures and occurs with very short chains. Moreover, the reverse exothermic reaction RI + HI ® RH + I 2 occurs very easily. When alkanes are iodinated, unsaturated compounds are also formed. For example, at 685° C, ethane, reacting with iodine, forms 72% ethylene and 10% acetylene. The same results were obtained with propane, butane and pentane.

The fluorination reaction of alkanes proceeds at a very high, often explosive, rate with the formation of all possible polyfluorinated derivatives of the original alkane. The energy released during the fluorination of alkanes is so great that it can lead to the breakdown of product molecules into radicals that begin new chains. As a result, the reaction rate increases like an avalanche and this leads to an explosion even at low temperatures. The peculiarity of the fluorination of alkanes is the possibility of destruction of the carbon skeleton by fluorine atoms with the formation of CF 4 as the final product with other halogens, such a reaction does not occur.

Nitration of alkanes (Konovalov’s reaction) also follows a radical mechanism: RH + NO 2 ® R· + HNO 2, R· + NO 2 ® RNO 2. The source of NO 2 is nitric acid, which decomposes when heated. The reaction is carried out in solution at temperatures above 150° C or in vapor under pressure up to 10 atm and a temperature of 400 – 500° C. In the latter case, C–C bonds in alkanes are also broken and a mixture of nitroalkanes is formed.

All alkanes burn by releasing heat, for example: C 5 H 12 + 8O 2 ® 5CO 2 + 6H 2 O. This reaction occurs, in particular, in the cylinders of internal combustion engines. To prevent the remains of unburned alkanes from entering the atmosphere, their catalytic afterburning is used in exhaust pipes (at the same time, CO is burned and nitrogen oxides are converted into harmless nitrogen). The reaction of oxygen with higher alkanes (in paraffin) occurs when a candle burns. Gaseous alkanes, such as methane, form explosive mixtures with air. Such mixtures can form in mines, as well as in residential buildings due to a leak of household gas if its content in the air reaches 5%.

Significant efforts of chemists were aimed at a detailed study of the reaction of low-temperature oxidation of alkanes in order to stop it at the stage of formation of valuable intermediate products - aldehydes, ketones, alcohols, carboxylic acids. Thus, in the presence of Co(II) and Mn(II) salts, butane can be oxidized to acetic acid, and paraffin to C12–C18 fatty acids. The oxidation of cyclohexane produces caprolactam, a monomer for the production of caprone, and adipic acid.

An important industrial reaction is the photochemical sulfochlorination of alkanes: a joint radical chain reaction with Cl 2 and SO 2 with the formation of alkanesulfonic acid chlorides RSO 2 Cl. This reaction is widely used in the production of detergents. When replacing chlorine with oxygen, a chain radical reaction of sulfonic oxidation of alkanes occurs with the formation of alkanesulfonic acids R–SO 2 –OH. Sodium salts of these acids are used as detergents and emulsifying agents.

At high temperatures, decomposition (pyrolysis) of alkanes occurs, for example: CH 4 ® C + 2H 2 (1000° C), 2CH 4 ® C 2 H 2 + 3H 2 (1500° C), C 2 H 6 ® C 2 H 4 +H2. The last reaction occurs at 500° C in the presence of a catalyst (Ni). Similarly, 2-butene CH 3 CH = CHCH 3 can be obtained from butane, at the same time a mixture of ethylene and ethane is formed. In contrast to this radical reaction, catalytic cracking of alkanes proceeds through an ionic mechanism and serves to produce gasoline from heavier petroleum fractions. When heated in the presence of Lewis acids, for example, AlCl 3, isomerization occurs: unbranched (normal) alkanes are converted into branched ones with the same number of carbon atoms. This reaction is of great practical importance for obtaining high-quality motor fuel ( cm. OCTANE NUMBER). Dehydrogenation of alkanes can be accompanied by ring closure (dehydrocyclization). In the case of hexane dehydrocyclization, the main product is benzene.

Methane at high temperature in the presence of a catalyst reacts with water vapor and carbon monoxide (IV) to form synthesis gas: CH 4 + H 2 O ® CO + 3H 2, CH 4 + CO 2 ® 2CO + 2H 2. Synthesis gas is used to produce motor fuels and methyl alcohol.

In recent years, the efforts of chemists have been aimed at creating catalysts that activate C–H bonds in alkane molecules under mild conditions. Some microorganisms “can” carry out such reactions, the enzymes of which are able to “digest” even paraffin with the formation of protein compounds. The task of chemists is to understand how natural catalysts work and to model enzymatic reactions that can occur at ordinary temperatures. In this case, various organometallic compounds are used as catalysts. For example, in the presence of some platinum compounds, methanol CH 3 OH can be obtained directly from methane, and in the presence of a triphenylphosphine complex of rhodium Rh[(C 6 H 5) 3 P] associated with CO molecules; During the reaction, CO molecules are introduced into the C–H bonds of alkanes to form aldehydes.

Cycloalkanes have chemical properties similar to alkanes. Thus, they are flammable, can be halogenated by a radical mechanism, and at elevated temperatures in the presence of catalysts they are dehydrogenated - they split off hydrogen and turn into unsaturated hydrocarbons. As mentioned, cyclopropane has special properties. Unlike alkanes, cycloalkanes are hydrogenated, when the ring opens and alkanes are formed, for example: cyclo-C 3 H 6 + H 2 ® C 3 H 8 (the reaction occurs when heated in the presence of a platinum catalyst). As the size of the cycle increases, the reaction becomes more difficult - thus, cyclopentane is already hydrogenated (to pentane) with great difficulty and at high temperatures (300 ° C).

Being in nature and receiving.

The main sources of alkanes are oil and natural gas. Methane makes up the bulk of natural gas; it also contains small amounts of ethane, propane and butane. Methane is found in emissions from swamps and coal seams. Along with light homologues, methane is present in associated petroleum gases. These gases are dissolved in oil under pressure and are also located above it. Alkanes make up a significant portion of petroleum products. Oil also contains cycloalkanes - they are called naphthenes (from the Greek. naphtha- oil). Gas hydrates of alkanes, mainly methane, are also widespread in nature; they occur in sedimentary rocks on continents and at the bottom of the oceans. Their reserves probably exceed the known reserves of natural gas and in the future may become a source of methane and its closest homologues.

Alkanes are also obtained by pyrolysis (coking) of coal and its hydrogenation (production of synthetic liquid fuel). Solid alkanes are found in nature in the form of deposits of mountain wax - ozokerite, in the waxy coatings of leaves, flowers and plant seeds, and are part of beeswax.

In industry, alkanes are produced by the catalytic hydrogenation of carbon oxides CO and CO 2 (Fischer–Tropsch method). In the laboratory, methane can be obtained by heating sodium acetate with a solid alkali: CH 3 COONa + NaOH ® CH 4 + Na 2 CO 3 , as well as by hydrolysis of some carbides: Al 4 C 3 + 12H 2 O ® 3CH 4 + 4Al(OH) 3 . Homologues of methane can be obtained by the Wurtz reaction, for example: 2CH 3 Br + 2Na ® CH 3 –CH 3 + 2NaBr. In the case of dihaloalkanes, cycloalkanes are obtained, for example: Br–CH 2 –(CH 2) 4 –CH 2 Br + 2Na ® cyclo-C 6 H 12 + 2NaBr. Alkanes are also formed during decarboxylation of carboxylic acids and during their electrolysis.

Application of alkanes.

Alkanes in gasoline, kerosene, diesel oil, and fuel oil are used as fuel. Higher alkanes are found in lubricating oils, petroleum jelly and paraffin. A mixture of isomeric pentanes and hexanes is called petroleum ether and is used as a solvent. Cyclohexane is also widely used as a solvent and for the synthesis of polymers (nylon, nylon). Cyclopropane is used for anesthesia. Squalane is a high-quality lubricating oil, a component of pharmaceutical and cosmetic preparations, and an adsorbent in gas-liquid chromatography.

Alkanes serve as raw materials for the production of many organic compounds, including alcohols, aldehydes, and acids. Chlorine derivatives of alkanes are used as solvents, for example, trichloromethane (chloroform) CHCl 3, carbon tetrachloride CCl 4. A mixture of higher alkanes - paraffin is non-toxic and is widely used in the food industry for impregnation of containers and packaging materials (for example, milk cartons), and in the production of chewing gum. Pencils and the upper (near the head) part of matches are impregnated with paraffin for better burning. Heated paraffin is used for medicinal purposes (paraffin treatment). Oxidation of paraffin under controlled conditions in the presence of catalysts (organic transition metal salts) leads to the production of oxygen-containing products, mainly organic acids.

Ilya Leenson

Literature:

Petrov A.A. Chemistry of alkanes. M., Nauka, 1974
Azerbaev I.N. and etc. Syntheses based on petroleum hydrocarbons. Alma-Ata, Science, 1974
Rudakov E.S. Reactions of alkanes with oxidizing agents, metal complexes and radicals in solutions. Kyiv, Naukova Dumka, 1985
Parauşanu V. Production and use of hydrocarbons. M., Chemistry, 1987



The names of the first ten members of the series of saturated hydrocarbons have already been given. To emphasize that an alkane has a straight 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, single-valent particles are formed called hydrocarbon radicals (abbreviated as 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:

Hydrocarbons/>
			C/>6/>H/>14/>
			C/>7/>H/>16/>
			C/>8/>H/>18/>
	C/>4/>H/>10/>		C/>9/>H/>20/>
	C/>5/>H/>12/>		C/>10/>H/>22/>
Monovalent radicals/>
			C/>6/>H/>13/> —/>
	C/>2/>H/>5/> — />		C/>7/>H/>15/> —/>
	C/>3/>H/>7/> — />		C/>8/>H/>17/> —/>
	C/> 4/> H/> 9/> —/>		C/> 9/> H/> 19/> —/>
Pentyl />(amyl)/>	C/>5/>H/>11/> —/>		C/>10/>H/>21/> —/>

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

When two hydrogen atoms are removed from a hydrocarbon molecule, divalent radicals are obtained. Their names are also derived from the names of the corresponding saturated hydrocarbons with the ending -ane replaced by -ylidene (if the hydrogen atoms are separated from one carbon atom) or -ylene (if the hydrogen atoms are removed from two adjacent carbon atoms). The radical CH 2 = is called methylene.

The names of radicals are used in the nomenclature of many hydrocarbon derivatives. For example: CH 3 I/> - methyl iodide, C 4 H 9 Cl/> -butyl chloride, CH 2 Cl/> 2/> - methylene chloride, C 2 H 4 B/>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)./>

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

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

Rational nomenclature is convenient for not very complex connections./>

According to substitutive 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 atoms of the chain are numbered from the end to which the hydrocarbon radical is closest. Then they call: 1) the number of the carbon atom to which the radical is associated (starting with the simplest radical); 2) a hydrocarbon that has a long chain. If the formula contains several identical radicals, then before their names indicate the number in words (di-, tri-, tetra-, etc.), and the numbers of the radicals are separated by commas. This is how hexane isomers should be called according to this nomenclature:/>

/>

Here's a more complex example:

Both substitutive 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 are used (formic acid, sulfuric ether, urea, etc.).

When writing the formulas of isomers, it is easy to notice that the carbon atoms occupy different positions in them. A carbon atom that is bonded to only one carbon atom in the chain is called primary, to two is called secondary, to three is tertiary, and to four is called 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 whether they are bonded to a primary, secondary, or tertiary carbon atom. This must always be taken into account./>