2 methyl methane. Alkanes - nomenclature, production, chemical properties

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: /\u003e

CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -C /\u003e H 2 /\u003e -CH 3 /\u003e

n-butane n-heptane /\u003e

(normal butane) (normal heptane)

When a hydrogen atom is removed from an alkane molecule, one-year particles are formed, called hydrocarbon radicals (abbreviated by 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:

Hydrocarbons /\u003e
		C /\u003e 6 /\u003e H /\u003e 14 /\u003e
		C /\u003e 7 /\u003e H /\u003e 16 /\u003e
		C /\u003e 8 /\u003e H /\u003e 18 /\u003e
	C /\u003e 4 /\u003e H /\u003e 10 /\u003e	C /\u003e 9 /\u003e H /\u003e 20 /\u003e
	C /\u003e 5 /\u003e H /\u003e 12 /\u003e	C /\u003e 10 /\u003e H /\u003e 22 /\u003e
Monovalent radicals /\u003e
		C /\u003e 6 /\u003e H /\u003e 13 /\u003e - /\u003e
	C /\u003e 2 /\u003e H /\u003e 5 /\u003e - /\u003e	C /\u003e 7 /\u003e H /\u003e 15 /\u003e - /\u003e
	C /\u003e 3 /\u003e H /\u003e 7 /\u003e - /\u003e	C /\u003e 8 /\u003e H /\u003e 17 /\u003e - /\u003e
	C /\u003e 4 /\u003e H /\u003e 9 /\u003e - /\u003e	C /\u003e 9 /\u003e H /\u003e 19 /\u003e - /\u003e
Pentyl /\u003e (amyl) /\u003e	C /\u003e 5 /\u003e H /\u003e 11 /\u003e - /\u003e	C /\u003e 10 /\u003e H /\u003e 21 /\u003e - /\u003e

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, and so on. /\u003e

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 from one carbon atom) or -ylene (if the hydrogen atoms are torn off from two adjacent carbon atoms). The radical CH 2 \u003d has the name methylene ./\u003e

Radical names are used in the nomenclature of many hydrocarbon derivatives. For example: CH 3 I /\u003e - methyl iodide, С 4 Н 9 Сl /\u003e - butyl chloride, СН 2 Сl /\u003e 2 /\u003e - methylene chloride, С 2 Н 4 В /\u003e r /\u003e 2 /\u003e - ethylene bromide (if bromine atoms are bonded to different carbon atoms) or ethylidene bromide (if bromine atoms are bonded to one carbon atom) ./\u003e

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) ./\u003e

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 ./\u003e

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 with 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 the hexane isomers should be called according to this nomenclature: /\u003e

And 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 the formulas for isomers, it is easy to notice that the carbon atoms occupy different positions in them. A carbon atom that is bound to only one carbon atom in the chain is called primary, with two as secondary, with three as tertiary, and with four as 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 ./\u003e

) 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:

methane - CH 4 ethane - CH 3 -CH 3 propane - CH 3 -CH 2 -CH 3 butane - CH 3 - (CH 2) 2 -CH 3 pentane - CH 3 - (CH 2) 3 -CH 3 hexane - CH 3 - (CH 2) 4 -CH 3 heptane - CH 3 - (CH 2) 5 -CH 3 octane - CH 3 - (CH 2) 6 -CH 3 nonane - CH 3 - (CH 2) 7 -CH 3 decane - CH 3 - (CH 2) 8 -CH 3

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 of 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 with the greatest number of branches is selected as the main one.

2 ... After establishing the main chain, it is necessary to number the carbon atoms. The numbering starts 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 smaller number of carbon atoms is closer (methyl, ethyl, propyl, etc.).

2,2,4-trimethylpent an

Wrong! 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 (the numerals are not taken into account), and the number corresponding to the number of the carbon atom of the main chain at which the radical is located is placed before 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, placing in order their ascents and put before the name of these 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:

methyl CH 3 - ethyl CH 3 -CH 2 - propyl CH 3 -CH 2 -CH 2 - butyl CH 3 -CH 2 -CH 2 -CH 2 - pentyl CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -

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").

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 of 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 starts 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, numbers indicate 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 ( 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).
During the passage of alkanes over the catalyst (Pt, Ni, A1 2 0 3, Cr 2 0 3) at high temperature (400-600 ° C), the hydrogen molecule is split off 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 has a very great importance when using alkanes as fuel:

In general terms, the reaction of alkane combustion 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 by exchanging a hydrogen atom to form 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 a state of sp 3 -hybridization. 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 or 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.