Limit (saturated) hydrocarbons hydrocarbons are called, in the molecules of which the carbon atoms are linked by a simple bond, and all the valence units not spent on the bond between the carbon atoms are saturated with hydrogen atoms.
Saturated hydrocarbons are methane CH 4; ethane C 2 H 6; propane C 3 H 8; butane C 4 H 10; pentane C 5 H 12; hexane C 6 H 14. However, this series can be continued. There are carbohydrates C 30 H 62, C 50 H 102, C 70 H 142, C 100 H 202.
If we consider hydrocarbons of the methane series, then it is easy to see that each subsequent hydrocarbon can be produced from the corresponding previous one by replacing one hydrogen atom with a CH 3 (methyl) group. Thus, the composition of the subsequent hydrocarbon molecule increases by the CH 2 group.
A number of chemical compounds of the same structural type, differing from each other by one or more structural units (usually by the CH 2 group), called homological series, and each of the carbohydrates – a member of the homologous series or homologue. If we arrange homologues in ascending order of their relative molecular weight, they form a homologous series.
The CH 2 group is called homologous difference or homologous difference. General formula of saturated hydrocarbons C n H 2 n + 2, where n – the number of carbon atoms in a molecule.
If a hydrogen atom is subtracted from a hydrocarbon molecule, then the remainder of the molecule with an open bond is called a hydrocarbon radical (denoted by the letter R). Because of their high reactivity, radicals do not exist in free form.
Homology phenomenon– the existence of ranks organic compounds, in which the formula of any two neighbors of the row differs by the same group (most often CH 2). The physicochemical properties of the compounds change in the course of the homologous series. In organic chemistry, the concept of homology is based on the fundamental position that chemical and physical properties compounds are determined by the structure of its molecules: these properties are determined by both the functional groups of the compound and its carbon skeleton.
The entire complex of chemical properties and, therefore, the assignment of a compound to a certain class is determined precisely by functional groups, but the degree of manifestation of chemical properties or physical properties depends on the carbon skeleton of the molecule.
In the absence of isomerism in the case of similarity of the carbon skeletons of compounds, the formula of homologous compounds can be written as X – (CH 2) n – Y, compounds with different numbers n of methylene units are homologous and belong to the same class of compounds. So, homologous compounds belong to the same class of compounds, and the properties of the nearest homologues are closest.
In homologous seriesthere is a certain regular change in properties from the younger members of the series to the older ones, but such a regularity is not always observed, in some cases it may be violated. Most often this occurs at the beginning of the series, because hydrogen bonds are formed in the presence of functional groups capable of their formation.
An example of a homologous series is a number of saturated hydrocarbons (alkanes).Its simplest representative – methane CH4. Homologues of methane are: ethane C 2 H 6; propane C 3 H 8; butane C 4 H 10; pentane C 5 H 12; hexane C 6 H 14, heptane C 7 H 16, octane - C 8 H 18, nonane - C 9 H 20, decane - C 10 H 22, undecane - C 11 H 24, nodecane – C 12 H 26, tridecane – S 13 N 28, tetradecan – C 14 H 30, pentadecane – C 15 H 32, eicosane - C 20 H 42, pentacosane - C 25 H 52, triacontane - C 30 H 62, tetracontane - C 40 H 82, hectane - C 100 H 202.
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In this article, the reader will find information about homologous compounds, find out what they are. General properties, formula of substances and their names, characteristics will be considered. In addition, not only the chemical understanding of homologues will be affected, but also the biological one.
What is a homologous series
Homologous series are chemical compounds that have a similar structural type, but differ in the number of repetitions of elementary units of a substance. The difference in structural components, namely, identical units, is called homologous difference. Homologues are substances that are in the same homologous series.
Examples of homologues include alcohols, alkanes, alkynes, ketones. If we consider the homologous series using the example of alkanes - the simplest representatives (characteristic formula: C n H 2 n + 2), then we see similarities in the structure of a number of representatives of this kind of substances: methane CH4, ethane C2H6, propane C3H8, and so on; CH2 methylene units are homologous differences in a number of these substances.
General concepts of the structure and homology of compounds
The concept of homology of substances in organic chemistry is based on the understanding that both physical and chemical qualitative characteristics of substances can be determined by molecular structure. The properties of homologous compounds can depend on the structure of the carbon skeleton and the functional group of a particular compound.
It is possible to determine the chemical properties and, therefore, the belonging of a homologue to a specific class by its functional group. As an example, you can pay attention to the carboxyl group, which is responsible for the manifestation of acidic properties and the belonging of a substance to carboxylic acids. However, it is possible to determine the level of manifestation of chemical or physical qualities by studying not only the functional group, but also the carbon molecular skeleton.
There are compounds in which the carbon skeletons are similar, in other words, there is no isomerism in them. Such homologues are written as follows: X - (CH 2) n - Y. The number of methylene n-unit units is homologous and belongs to the class of compounds of the same type. These kinds of homologues are the closest.
The homologous series of substances carries some general patterns changes in properties from younger representatives to older ones. A similar phenomenon can be violated, which is associated with the formation of a hydrogen bond in the presence of a group that can form them.
Homology of aldehydes
Aldehydes are a number of organic-type compounds containing an aldehyde group - COH. In substances of this type, the carboxyl group is interconnected with a hydrogen atom and one radical group.
The homologous series of aldehydes has the general formula R-COH. One of the elementary representatives is formaldehyde (H-COH), in which the aldehyde group is linked to H. In other, limiting representatives of this series of compounds, the hydrogen atom is replaced by an alkyne. General formula: C n C 2 n + 1 -COH.
Aldehydes are considered as substances that have occurred as a result of the replacement of a paraffinic hydrocarbon atom H by an aldehyde group. For such chemical compounds isomerism and homology is similar to other derivatives of saturated monosubstituted hydrocarbons.
The name of aldehydes is compiled depending on the name of the acid with the same number of carbon atoms in the molecule, for example: CH3-CHO - acetaldehyde, CH3CH2-CHO - propionic aldehyde, (CH3) 2CH-CHO - isobutyraldehyde, etc.
Alkyne homology
Alkynes are hydrocarbon chemical compounds that carry triple bonds between C atoms. They form a series of homologues with the characteristic formula C n H 2 n-2. Common feature the position of a carbon atom with a triple number of bonds is the sp-hybridization state.
Homologous series of alkynes: ethyne (C2H2), propyne (C3H4), butyne (C4H6), pentine (C5H8), hexine (C6H10), heptine (C7H12), octine (C8H14), nonine (C9H16), decin (C10H18).
The physical properties of alkynes are determined in a similar way to alkenes. For example, boiling and melting points gradually increase with increasing carbon main chain length and molecular weight. Chemical properties include halogenation, hydrohalogenation, hydration, and polymerization reactions. Substitution reactions are also characteristic of alkynes.
Homology in biology
The homologous series is used in biology, but has a slightly different character. NI Vavilov discovered the law according to which the origin of species and even genera of plants, similar to each other, entails the course of variability along parallel paths. Genera and species characterized by genetically similar hereditary changes can serve as a way to determine changes in the manifestation of traits for other, related species. As in the chemical table of D.I.Mendeleev, the homological law makes it possible to determine and predict the existence of unknown taxonomic units of plants with selective characteristics that are valuable. This law was formulated through the study of parallelisms, manifested in the hereditary variability of generations.
Conclusion
A homologous series of substances characterized by a general formula structure, but differing in homologous difference, allowed a person to increase the chemical potential of substances, discover and obtain many new compounds used in all spheres of life. Better understand the fundamental phenomenon that physical and chemical quality characteristics can be determined by the molecular structure of a compound.
From Wikipedia, the free encyclopedia
Homologous series - a number of chemical compounds of the same structural type (for example, alkanes or aliphatic alcohols - fatty alcohols), differing from each other in composition by a certain number of repeating structural units - the so-called homologous difference. Homologues - substances included in the same homologous series.
The simplest example of a homologous series is alkanes (general formula C n H 2n + 2): methane CH 4, ethane C 2 H 6, propane C 3 H 8, etc .; the homologous difference of this series is the methylene unit —CH 2 -.
Homology and structure of compounds
The concept of homology in organic chemistry is based on the fundamental thesis that the chemical and physical properties of a substance are determined by the structure of its molecules: these properties are defined as the functional groups of the compound (hydroxyl of alcohols, carboxyl group of carboxylic acids, aryl group of aromatic compounds, etc.) and its carbon skeleton.
The complex of chemical properties itself and, accordingly, the belonging of a compound to a certain class is determined precisely by functional groups (for example, the presence of a carboxyl group determines the manifestation of acidic properties by a compound and its belonging to the class of carboxylic acids), but by the degree of manifestation of chemical properties (for example, reactivity and dissociation constant) or physical properties (boiling and melting points, refractive index, etc.) are also influenced by the carbon skeleton of the molecule (see Fig. 1).
In the case of similarity of the carbon skeletons of compounds, that is, the absence of isomerism, the formula of homologous compounds can be written as X- (CH 2) n -Y, connections with a different number n methylene units are homologues and belong to the same class of compounds (for example, H- (CH 2) n -COOH - aliphatic carboxylic acids). Thus, homologous compounds belong to the same class of compounds, and the properties of the nearest homologues are closest.
In homologous series, there is a regular change in properties from the younger members of the series to the older ones, however, such a regularity can be violated, first of all, at the beginning of the series, due to the formation of hydrogen bonds in the presence of functional groups capable of their formation (see Fig. 2, melting point).
In the study of parallelisms in the phenomena of hereditary variability, N.I. Vavilov, by analogy with homologous series of organic compounds, introduced the concept Homologous series in hereditary variation.
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An excerpt characterizing the homological series
After Prince Andrey, Boris approached Natasha, inviting her to dance, the dancer adjutant who had started the ball, and other young people approached Natasha, and Natasha, handing over her unnecessary gentlemen to Sonya, happy and flushed, did not stop dancing the whole evening. She did not notice or see anything that occupied everyone at this ball. She not only did not notice how the sovereign spoke for a long time with the French envoy, how he spoke especially graciously with such and such a lady, how the prince such and such did and said how Helene had great success and received special attention such and such; she did not even see the sovereign and noticed that he left only because after his departure the ball became more lively. One of the merry cotillions, before supper, Prince Andrew again danced with Natasha. He reminded her of their first date in the Otradnenskaya alley and how she could not sleep on a moonlit night, and how he could not help hearing her. Natasha blushed at this reminder and tried to justify herself, as if there was something embarrassing in the feeling in which Prince Andrew had involuntarily overheard her.
Prince Andrew, like all people who grew up in the world, loved to meet in the world that which did not have a common secular imprint. And such was Natasha, with her surprise, joy and timidity, and even mistakes in French. He treated and spoke with her especially tenderly and carefully. Sitting beside her, talking to her about the simplest and most insignificant subjects, Prince Andrey admired the joyful sparkle of her eyes and her smile, which was not related to the speeches being spoken, but to her inner happiness. While Natasha was being chosen and she stood up with a smile and danced around the hall, Prince Andrei admired especially her timid grace. In the middle of the cotillion Natasha, having finished her figure, still breathing heavily, approached her place. The new gentleman invited her again. She was tired and out of breath, and apparently thought to refuse, but immediately again gaily raised her hand on the gentleman's shoulder and smiled at Prince Andrew.
“I would be glad to have a rest and sit with you, I am tired; but you see how they choose me, and I am happy about it, and I am happy, and I love everyone, and we all understand this, ”and this smile said a lot. When the gentleman left her, Natasha ran across the hall to take two ladies for the figures.
“If she comes up first to her cousin, and then to another lady, then she will be my wife,” Prince Andrew said quite unexpectedly to himself, looking at her. She went first to her cousin.
“What nonsense sometimes comes to mind! thought Prince Andrew; but it is only true that this girl is so sweet, so special that she will not dance here for a month and will get married ... This is a rarity here, ”he thought when Natasha, straightening the rose that had leaned back from the bodice, sat down beside him.
At the end of the cotillion, the old count, in his blue dress coat, walked up to the dancers. He invited Prince Andrew to his place and asked his daughter if she was having fun? Natasha did not answer and only smiled with such a smile, which reproachfully said: "how could you ask about this?"
- As fun as ever! She said, and Prince Andrew noticed how quickly her thin arms rose to hug her father and immediately dropped down. Natasha was as happy as never before in her life. She was at that highest stage of happiness, when a person becomes completely trusting and does not believe in the possibility of evil, unhappiness and grief.
Pierre at this ball for the first time felt offended by the position that his wife held in the higher spheres. He was morose and absent-minded. There was a wide fold across his forehead, and he, standing by the window, looked through his glasses, not seeing anyone.
Natasha, heading for dinner, walked past him.
Pierre's gloomy, unhappy face startled her. She stopped opposite him. She wanted to help him, to convey to him the surplus of her happiness.
“How fun, Count,” she said, “isn't it?
Pierre smiled absently, obviously not understanding what was being said to him.
“Yes, I'm very glad,” he said.
“How can they be dissatisfied with something, Natasha thought. Especially as good as this Bezukhov? " In Natasha's eyes, all those who were at the ball were equally kind, sweet, wonderful people, loving each other: no one could offend each other, and therefore everyone should be happy.
The next day, Prince Andrei recalled yesterday's ball, but did not dwell on it for long with his thoughts. “Yes, it was a very brilliant ball. And yet ... yes, Rostova is very nice. There is something fresh, special, not Petersburg-style in her that distinguishes her. " That's all he thought about yesterday's ball, and after drinking tea, sat down to work.
But from fatigue or insomnia (the day was not a good one for studies, and Prince Andrey could not do anything), he kept criticizing his own work, as it often happened to him, and was glad when he heard that someone had arrived.
The newcomer was Bitsky, who served in various commissions, who was in all societies of St. Petersburg, a passionate admirer of new ideas and Speransky and an anxious messenger of St. Petersburg, one of those people who choose a direction like a dress - fashion, but who therefore seem to be the most ardent partisans of the direction ... He anxiously, barely having time to take off his hat, ran to Prince Andrey and immediately began to speak. He had just learned the details of the meeting of the State Council this morning, opened by the Emperor, and was talking about it with enthusiasm. The sovereign's speech was extraordinary. It was one of those speeches that are only given by constitutional monarchs. “The sovereign said directly that the council and the senate are the essence of the state estates; he said that government should be based not on arbitrariness, but on firm principles. The sovereign said that finances must be transformed and reports must be made public, ”Bitsky said, striking at famous words and opening his eyes significantly.
Homological series
Figure: 2 - Melting points (blue) and boiling points (purple) in the homologous series of aliphatic carboxylic acids C1 ... C8.
Homological series - a number of chemical compounds of the same structural type (for example, alkanes or aliphatic alcohols - fatty alcohols), differing from each other in composition by a certain number of repeating structural units - the so-called "homologous difference". Most often these are methylene units: ... -CH 2 - ... The simplest example of a homologous series is the lower homologues of alkanes (general formula C n H 2n + 2): methane CH 4, ethane C 2 H 6, propane C 3 H 8, etc. ...
Homology and structure of compounds
The concept of homology in organic chemistry is based on the fundamental thesis that the chemical and physical properties of a substance are determined by the structure of its molecules: these properties are defined as the functional groups of the compound (hydroxyl of alcohols, carboxyl group of carboxylic acids, aryl group of aromatic compounds, etc.) and its carbon skeleton.
The complex of chemical properties itself and, accordingly, the belonging of a compound to a certain class is determined precisely by functional groups (for example, the presence of a carboxyl group determines the manifestation of acidic properties by a compound and its belonging to the class of carboxylic acids), but by the degree of manifestation of chemical properties (for example, reactivity and dissociation constant) or physical properties (boiling and melting points, refractive index, etc.) are also influenced by the carbon skeleton of the molecule (see Fig. 1).
In the case of similarity of the carbon skeletons of compounds, that is, the absence of isomerism, the formula of homologous compounds can be written as X- (CH 2) n -Y, connections with a different number n methylene units are homologues and belong to the same class of compounds (for example, H- (CH 2) n -COOH - aliphatic carboxylic acids). Thus, homologous compounds belong to the same class of compounds, and the properties of the nearest homologues are closest.
In homologous series, there is a regular change in properties from the younger members of the series to the older ones, however, such a regularity can be violated, first of all, at the beginning of the series, due to the formation of hydrogen bonds in the presence of functional groups capable of their formation (see Fig. 2, melting point).
In the study of parallelisms in the phenomena of hereditary variability, N.I. Vavilov, by analogy with homologous series of organic compounds, introduced the concept Homologous series in hereditary variation.
see also
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See what "Homological series" is in other dictionaries:
HOMOLOGICAL RANGE - (by this, see the next word). A number of chemical compounds that are similar in properties, functions, reactions, and the reaction products are also homologous. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910 ... Dictionary of foreign words of the Russian language
HOMOLOGICAL RANGE - in chemistry (from the Greek homologos, correspondingly similar), a sequence of organic compounds with the same functional groups and the same structure, each member of which differs from the neighboring one by a permanent structural unit ... ... Big Encyclopedic Dictionary
HOMOLOGICAL RANGE - a group of organic compounds with similar functional groups and the same structure, each member of which differs from the neighboring one by one million several permanent structural units (homologous difference), most often by the CH2 group in ... ... Big Polytechnic Encyclopedia
homologous series - in chemistry (from the Greek homólogos, corresponding, similar), a sequence of organic compounds with the same functional groups and the same structure, each member of which differs from the neighboring one by a permanent structural unit ... ... encyclopedic Dictionary
homologous series - homologinė eilė statusas T sritis chemija apibrėžtis Organinių junginių eilė, kurios gretimi nariai skiriasi –CH₂– grupe. atitikmenys: angl. homologous series rus. homologous series ... Chemijos terminų aiškinamasis žodynas
HOMOLOGICAL RANGE - sequence of org. conn. with the same func. groups and a similar structure, each member of the swarm differs from the neighboring one by a constant structural unit (homologous difference), most often the methylene group ČSN 2 Ch. Members of G. p. called ... ... Chemical encyclopedia
HOMOLOGICAL RANGE - in chemistry (from the Greek homologos corresponding, similar), the sequence is organic. conn. with the same functional groups and the same structure, each member of the swarm differs from the neighboring one at the post. structural unit (homologous difference) ... Natural science. encyclopedic Dictionary
homologous hydrocarbon series - - Topics oil and gas industry EN hydrocarbon family ... Technical translator's guide
RANGE OF HYDROCARBONS HOMOLOGICAL - [γομςο (homos) the same, similar] gr. hydrocarbons with a characteristic structure and general formula, as well as with a certain generality of chemical. properties .. Neighboring members of a city differ from each other in composition by one ... ... Geological encyclopedia
Alkanes - This article is about chemical compounds... For the Canadian aluminum company see Rio Tinto Alcan ... Wikipedia