Organic chemistry

from Wikipedia, the free encyclopedia
Classic molecular structure of organic chemistry - Kekulé's benzene formula depicted on a 1964 postage stamp

The organic chemistry (short OC or often also organic ) is a branch of chemistry . This covers the chemical compounds that are based on carbon , with a few exceptions such as some inorganic carbon compounds and elemental (pure) carbon.

The great bonding capacity of the carbon atom enables a multitude of different bonds to other atoms. While many inorganic substances are not changed by the influence of temperature and catalytic reagents, organic reactions often take place at room temperature or slightly elevated temperature with catalytic amounts of reagents. The formation of the multitude of natural substances (vegetable, animal dyes , sugar , fats , proteins , nucleic acids ) and ultimately of the known living beings is also based on this ability to bind.

In addition to carbon, organic molecules often contain hydrogen , oxygen , nitrogen , sulfur and halogens as elements ; the chemical structure and the functional groups are the basis for the diversity of the individual molecules.

In organic analysis, a mixture of substances is first used to physically separate and characterize individual substances ( melting point , boiling point , refractive index ), then the elemental composition ( elemental analysis ), molecular mass and functional groups (with the help of chemical reagents, NMR , IR - and UV spectroscopy ).

The effect of reagents ( acids , bases , inorganic and organic substances) on organic substances is investigated in order to determine the laws of chemical reagents on certain functional groups and substance groups.

Organic chemistry synthesizes organic natural substances (e.g. sugar, peptides, natural dyes, alkaloids, vitamins) as well as organic substances unknown in nature (plastics, ion exchangers, pharmaceuticals , pesticides, synthetic fibers for clothing).

The developments in organic chemistry over the past 150 years have had a significant impact on human health, nutrition, clothing, and the variety of consumer goods available. It contributed greatly to the prosperity of a society.

Differentiation from inorganic chemistry

With a few exceptions, organic chemistry comprises the chemistry of all compounds that carbon forms with itself and with other elements. This also includes all the building blocks of currently known life. In 2012 around 40 million organic compounds were known.

The exceptions include formal first the elemental forms of carbon ( graphite , diamond ) and systematically all the inorganic chemistry counting hydrogen-free chalcogenides of carbon ( carbon monoxide , carbon dioxide , carbon disulfide ), the carbonic acid and carbonates , the carbides and the ionic cyanides , cyanates and thiocyanates ( see carbon compounds ).

The hydrocyanic acid is part of the border area of the inorganic and organic chemistry. Although it would traditionally be counted as part of inorganic chemistry, it is regarded as the nitrile (organic group of substances) of formic acid . The cyanides are treated in the inorganic, whereby only the salts of hydrogen cyanide are meant here, whereas the esters known under the same name belong to the organic as nitriles. The cyanoic acids , thiocyanic acids and their esters are also considered borderline cases. Furthermore, organometallic chemistry ( organometallic chemistry ) is not specifically assigned to organic or inorganic chemistry.

Completely unnatural-looking substances, such as plastics and petroleum , are also organic compounds because, like natural substances, they consist of carbon compounds. Crude oil, natural gas and coal, the starting materials for many synthetic products, are ultimately of organic origin.

All living things contain organic substances such as amino acids , proteins , carbohydrates and DNA . The branch of organic chemistry that deals with the substances and metabolic processes in living beings is biochemistry (or molecular biology ).


The special position of carbon is based on the fact that the carbon atom has four bonding electrons, which means that it can form non-polar bonds with one to four other carbon atoms. This can lead to the formation of linear or branched carbon chains and carbon rings that are bonded to hydrogen and other elements (mainly oxygen, nitrogen, sulfur, phosphorus) at the binding electrons that are not occupied by carbon, resulting in large and very large molecules (e.g. homo- and heteropolymers ) and explains the huge variety of organic molecules. There are also a large number of compounds of the likewise four-bonded silicon , but far from such a variety.

The properties of organic substances are very much determined by their respective molecular structure . Even the properties of simple organic salts like the acetates are clearly shaped by the molecular shape of the organic part. There are also many isomers , i.e. compounds with the same overall composition ( molecular formula ) but different structure ( structural formula ).

In contrast, the molecules in inorganic chemistry usually consist of only a few atoms, in which the general properties of solids, crystals and / or ions come into play. But there are also polymers that contain no carbon (or only in subgroups), e.g. B. the silanes .

Organic synthesis strategies differ from syntheses in inorganic chemistry, since organic molecules can usually be built up piece by piece. Around 60% of chemists in Germany and the USA have chosen organic chemistry as a major.


Many organic natural substances were used in the early days of human development (the colorants indigo , alizarin , essential oils, alcohol ). However, an artificial representation of organic substances by human hands has not been described in a very early period.

In his works, Johann Rudolph Glauber described a large number of organic compounds he presented himself, but since elemental analysis had not yet been developed, one can only guess which substances he had received at that time. Glauber purified alcohol and vinegar using fractional distillation, he obtained ethyl chloride from alcohol , acetic acid from wood distillation, acetone from the heating of zinc acetate, acrolein was formed from the distillation of beet, nut and hemp oil, benzene from coal, he found alkaloids through a nitric acid separation.

Lemery wrote the book Cours de Chymie in 1675 . In this work, the substances were divided into three areas: mineral kingdom (metals, water, air, table salt, gypsum), vegetable kingdom (sugar, starch, resins, wax, vegetable dyes), animal kingdom (fats, proteins, horny substances). Lemery also differentiated the substances of the plant and animal kingdoms as organic substances in contrast to the substances of the inanimate nature of the mineral kingdom.

A considerable number of organic substances had already been isolated as pure substances in the 18th century .

Examples are urea (1773 Hilaire Rouelle ) and many acids , such as those of ants obtained formic acid (1749 by Andreas Sigismund Marggraf ), the malic acid from apples , and from the Weinstein obtained tartaric acid (1769), the citric acid (1784), the glycerol (1783), the oxalic acid , uric acid (by Carl Wilhelm Scheele ).

Antoine Laurent de Lavoisier was the first to qualitatively determine the chemical elements contained in organic substances: carbon, hydrogen, oxygen, nitrogen. Joseph Louis Gay-Lussac and Louis Jacques Thenard carried out the first elemental analyzes to determine the quantitative composition of elements in organic substances. The elemental analysis was improved by Justus von Liebig in 1831 . The elementary composition of organic substances could now be determined quickly.

Jöns Jakob Berzelius put forward the thesis that organic substances can only be created by a special life force in the plant, animal or human organism. His little book, Overview of the Advances and Current State of Animal Chemistry, marked the beginning of organic chemistry, which emerged in the first half of the 19th century, in 1810. Berzelius also applied the law of multiple proportions - with which he used atomic weights and composition in the field of inorganic compounds, i.e. H. whose chemical formulas could also determine organic compounds.

The structure and composition of organic compounds was still very unclear around 1820. Gay-Lussac believed that the ethanol was a combination of one part ethene and one part water.

Furthermore, the chemists believed at the time that with the same qualitative and quantitative composition (empirical formula) of the elements of a compound (elemental analysis), the substances must also be identical. The first doubts arose in 1823 when Justus von Liebig and Friedrich Wöhler examined the highly acidic silver and the cyanoic silver. They found very different substances with the same chemical composition.

When the inorganic compound ammonium cyanate is heated, urea, a typical organic compound, is produced. This is the famous urea synthesis by Friedrich Wöhler, which led to a paradigm shift .

In 1828 Friedrich Wöhler heated ammonium cyanate and received a completely different substance, urea . The starting product and the end product have the same chemical molecular formula ( isomerism ), but they have very different properties: ammonium cyanate is an inorganic compound, urea is an organic compound. This refuted Berzelius' hypothesis that organic compounds can only arise through a special life force .

In 1859 Hermann Kolbe formulated the thesis that all organic substances are derivatives of inorganic substances - especially carbon dioxide. Replacing a hydroxyl group with alkyl radicals or hydrogen gives carboxylic acids, and replacing two hydroxyl groups with alkyl groups or hydrogen results in aldehydes , ketones . Kolbe also used the word synthesis in connection with the artificial representation of organic natural substances. Chemists were soon able to synthesize new organic molecules through their own research.

In analogy to positively and negatively charged ions in inorganic chemistry, Berzelius suspected so-called radicals in organic chemistry; his radical theory was based on this. One radical part of the organic molecule should have a positive, the other part a negative charge. A few years later, Jean Baptiste Dumas , Auguste Laurent , Charles Gerhardt and Justus von Liebig investigated substitution in organic compounds. The hydrogen atoms in organic compounds have been replaced with halogen atoms. The old radical theory of Berzelius, according to which positively and negatively charged radical parts accumulate in organic molecules, had to be rejected. As a result, August Wilhelm von Hofmann , Hermann Kolbe , Edward Frankland , and Stanislao Cannizzaro found further information about the composition of organic substances. In 1857 Friedrich August Kekulé published his work “About the s. G. paired compounds and the theory of polyatomic radicals ” in Liebig's Annals of Chemistry , which is seen as the starting point for organic structural chemistry . In this work, carbon is described as tetravalent for the first time.

Adolf von Baeyer , Emil Fischer , August Wilhelm von Hofmann researched syntheses of dyes, sugars, peptides and alkaloids.

A large part of the working time of the former chemists was the isolation of a pure substance.

The substance identity of organic substances was checked using boiling point , melting point , solubility, density, odor, color, and refractive index .

The raw material coal became particularly important for organic chemistry. Organic chemistry took off when the German chemist Friedlieb Ferdinand Runge (1795–1867) discovered the substances phenol and aniline in coal tar . William Henry Perkin - a student of August Wilhelm von Hofmann - discovered the first synthetic dye - mauvein - in 1856 . Hofmann and Emanuel Verguin introduced the fuchsin to dyeing. Johann Peter Grieß discovered the diazo dyes. Organic chemistry now gained increasing industrial and economic importance.

In the 1960s, the preparation of valence isomers of benzene was achieved through complex organic syntheses. A non-classical carbocation was found earlier with the 2-norbornyl cation, which forms five instead of three bonds to other atoms. In 1973, the pentagonal-pyramidal hexamethylbenzene dication with six-coordinate carbon was synthesized for the first time, the structure of which was crystallographically demonstrated in 2016.

Basics of organic synthesis in school and university

Organic chemistry is a branch of science (textbooks, studies), the basics of which were only accessible to a small section of the population in the 19th century. The educational reforms of the 20th century gave almost all students a knowledge base in organic chemistry. The chemistry class enables the student to participate in cultural education, promotes an understanding of the classification and context of questions that are chemically relevant. In our culture, politicians, lawyers, business economists, computer scientists and mechanical engineers need basic knowledge of organic chemistry in order to better classify relationships.

Conversions of organic substances in the laboratory

In earlier times, for example, organic chemists examined the influence of concentrated acids ( sulfuric acid , nitric acid , hydrochloric acid ) on organic substances such as ethanol , cotton, and benzene .

The action of concentrated sulfuric acid on ethanol creates a new substance, diethyl ether , which had completely different properties than ethanol and was used as an anesthetic and as a new solvent. The action of nitric acid and sulfuric acid on cotton produces gun cotton , which was used as an explosive, as a plasticizer and as a solvent for paints , as fibers.

Nitric benzene is formed from benzene through the action of concentrated sulfuric acid and nitric acid . This substance could be converted into aniline with reducing agents such as iron powder and hydrochloric acid . Aniline was the starting material for many new dyes that increased the prosperity of our community.

The action of concentrated sulfuric acid on cotton or wood results in sugar molecules. As in inorganic chemistry, organic chemists also used certain detection reagents. For organic chemists, however, the functional groups in the molecule are of great importance. Aldehyde groups can be detected with Fehling's solution . Functional groups can be used to link two organic molecules with different functional groups so that a larger molecule is created. By knowing the organic reaction mechanisms, the choice of reagents and the use of protective groups , an organic chemist can produce very complex organic substances. Nowadays, peptides or proteins with more than 100 amino acids (with a molecular mass greater than 10,000) or carbohydrates and phytonutrients ( terpenes ) can be synthesized. Hardly any organic reaction takes place with 100% yield, and there are often unexpected side reactions, so that complex synthetic-based substances are only produced in small quantities (a few milligrams to several kilograms).

Many organic raw materials are produced in the industry in the manufacture of plastics, dyes, solvents in very large quantities (1,000 to 1,000,000 t). Specialized companies use the industrial products to manufacture fine chemicals for schools and universities. The organic chemist wants reagents that are as selective as possible in their syntheses, which oxidize, reduce or link only a certain functional group to another group.

Influence of temperature on organic reactions

Sometimes metabolism is only possible at an increased temperature. However, high temperatures are rarely used in organic chemistry, as many organic substances are destroyed by an increased temperature. The reaction temperatures in organic chemistry are therefore usually between room temperature and 150 ° C. The choice of solvent and its boiling point are decisive for setting the reaction temperature. A temperature increase of 10 ° C usually doubles the reaction rate ( RGT rule ).

Examples of organic reactions at high temperatures are the formation of acetone from calcium acetate and the preparation of 2,3-dimethyl-butadiene from pinacol .

The organic salt calcium acetate can be prepared from calcium carbonate and acetic acid . If the calcium acetate is heated to approx. 400 ° C, acetone is obtained. Acetone and a little magnesium form the organic substance pinacol. If this substance is heated with aluminum oxide at 450 ° C., 2,3-dimethyl-1,3-butadiene is formed. Substances with double bonds can be polymerized under the influence of an acid or radical formers, resulting in a plastic with completely different properties than the monomer. The polymerized 2,3-dimethyl-1,3-butadiene played an important role as a substitute for rubber, which used to be very expensive . Fritz Hofmann was able to produce the first synthetic methyl rubber from 2,3-dimethyl-1,3-butadiene , which came on the market in 1913 when the price for natural rubber reached highs in the trade.

Work-up after implementation

After a chemical conversion, the organic chemist must first convert the highly reactive, caustic, flammable substances such as concentrated sulfuric acid, sodium , sodium hydride , lithium aluminum hydride with suitable substances into harmless compounds. This is followed by the separation of the inorganic salts by shaking them out in a separating funnel - with the addition of further organic solvents and an aqueous solution. The organic phase is dried over anhydrous salts such as sodium sulfate , the last residues of water are removed from the organic phase. The organic solvent is removed by distillation - often on a rotary evaporator . The evaporated residue contains the reaction product. Very rarely does an organic reaction result in only one chemical product; in many cases, mixtures of different organic substances arise. The individual substances can be isolated by fractional distillation in vacuo or by column chromatography .

Structural chemical formula and reaction mechanism

The chemical structural formula is the basis for knowledge of the substance . This is the blueprint of an organic molecule. The structural formula of a substance must always be derived from the results of the substance analysis. The substance analysis includes at least the correct carbon, hydrogen, oxygen and nitrogen content of a molecule ( elemental analysis ), the type of functional groups and the determination of the molar mass .

Through the commercial sale of nuclear magnetic resonance spectroscopy ( NMR spectroscopy ) and mass spectrometers at universities since the beginning of the sixties, the time until the structure elucidation of new, complicated organic substances has been shortened considerably. By changing the structural formula before and after an organic reaction, the chemist can derive the reaction mechanism of a chemical reaction. All organic molecules with a similar structure can enter into similar reactions under the same reaction conditions. Knowing the reaction mechanisms, the chemist can systematically plan the structure of new organic substances.

A very important class of reactions relates to the replacement of a hydrogen atom in the molecule with a halogen, a nitro group, a sulfone group; this reaction is called substitution. A few examples from this reaction class were given at the beginning of this section. Another important class of reactions is elimination . The elimination of hydroxyl groups and halogens and the formation of double bonds in the molecule is known as elimination. The elimination of water with pinacol to 2,3-dimethyl-1,3-butadiene is an elimination. Other very important transformations are the oxidation and reduction of organic molecules. The reduction of nitrobenzene to aniline by zinc or iron filings in the presence of an acid or the oxidation of ethanol to acetaldehyde or acetic acid by means of potassium permanganate are examples of these reaction classes.

Importance of organic chemistry

Smells and flavors from strawberries
Fragrances of the rose
Acetylsalicylic acid (aspirin) - almost all drugs are organic

Substances of organic chemistry are present in almost all goods we use every day. The dyes in picture books, magazines, packaging, the plastics in the majority of our consumer goods in almost every toy, in computer cases , in pipes, cables, carrier bags, etc., the organic synthetic fibers in most of our clothing, the paints for house facades, cars, the living area , the cleaning agents from simple soaps to complex surfactants for special applications, the pharmaceuticals , the aromas and fragrances in food and flowers, the food preservatives, the ion exchangers in desalination plants. Wood and cotton are also organic substances, they can be obtained from nature because they are abundant. The majority of organic substances, however, have to be produced on a synthetic basis - mainly from petroleum - by the chemical industry. In the event of a worldwide shortage of crude oil, other fossil raw materials such as coal or natural gas could currently only be used to a limited extent to produce the organic substances we need every day. A high price for crude oil leads to efforts to develop substitution processes based on coal and natural gas. However, the processes will be less profitable than those based on petroleum. With very high prices for crude oil, there could be shortages in the area of ​​consumer goods.

Organic chemical industry

Basic chemicals

Basic chemicals are the basis for all important synthetic materials. They are made in large chemical plants from crude oil , natural gas or coal .

Until the Second World War, coal was the basis for the basic chemicals in organic chemistry. Benzene , toluene and xylene - building blocks for organic dyes - could be extracted from coal . Calcium carbide (on an industrial scale since 1915) can be extracted from coal and lime with an electric arc . Calcium carbide can be converted into acetylene and at that time it formed the starting material for acetaldehyde, acetic acid, acetone, butylene glycol, butadiene, acrylic acid and acrylonitrile using the Walter Reppe (Reppe Chemie) method. Methanol (synthesis according to Pier) and diesel oil (according to Bergius) could also be obtained from coal . Even after the Second World War, many basic chemicals were still made from coal. Between 1960 and 1970, the processes in the western industrialized countries were replaced by more modern processes based on petroleum.

The investment costs for such systems are considerable, mainly companies in the mineral oil industry are involved in this business area. In the past, chemical raw materials were transported to industrialized countries and chemically converted into basic chemicals there. In the 1980s the USA, Japan and the Federal Republic of Germany were the most important chemical countries with more than 50% of the world production of organic raw materials. In the course of global interdependence and for economic reasons, many plants are being built in the raw material countries (for oil and natural gas).

Very important basic chemicals are ethylene (19.5 million tonnes in EU-27, 2011), propene (14.3 million t, EU-27, 2011), butadiene (2.8 million t, EU-27, 2011) , Methane , benzene (7.4 million t, EU-27, 2011), toluene (1.5 million t., EU-27, 2011), xylene . Other important organic raw materials can be produced from these basic chemicals. The sales prices in the EU for organic raw materials have fluctuated considerably since 2005, and sales prices in the EU rose significantly in 2010.

The industry extracts polyethylene , vinyl acetate (hereinafter polyvinyl acetate, polyvinyl alcohol , polyvinyl acetal ), acetaldehyde , acetic acid , dichloroethane (hereinafter polyvinyl chloride ), ethylene oxide , ethanol (hereinafter diethyl ether ) from ethylene .

Of propylene company polypropylene, gain isopropanol (hereinafter, acetone , ketene , acetic anhydride , diketene, Essigsäureester , acetyl), propylene oxide (hereinafter referred to polyether polyols, polyurethane ), allyl chloride (hereinafter, epichlorohydrin , glycerol , allyl alcohol ), acrylonitrile (hereinafter referred to polyacrylonitrile , acrylamide ), acrylic acid ( hereinafter polyacrylates ), butanol .

Methanol (hereinafter formaldehyde and ethylene glycol), acetylene, methyl chloride, methylene chloride, chloroform (hereinafter tetrafluoroethylene, Teflon) and carbon tetrachloride are obtained from methane .

Ethylbenzene (hereinafter styrene ), dihydroxybenzene ( resorcinol , hydroquinone and pyrocatechol ), cumene (hereinafter phenol ), nitrobenzene (hereinafter aniline , dyes ), cyclohexane (hereinafter cyclohexanone , adipic acid , nylon ) are synthesized from benzene . Terephthalic acid and phthalic anhydride can be produced from xylene .

Industrial products, special products

This swimming aid is made of foamed polystyrene , encased in colored polyethylene , both plastics.

Industrial products are predominantly mixtures of organic substances that have been prepared for application-specific production. Industrial products are manufactured in very large quantities (up to several million tons) by the chemical industry, with these products the raw material costs are very decisive for the sales price.

Important organic industrial products are: chemical fibers , plastics , colorants , rubber , solvents , tensides . Sales for plastics have declined significantly since 2009.

Special products are organic substances that are produced in significantly smaller quantities compared to industrial products. The selling price is less dependent on raw material costs. This group includes, for example, pharmaceuticals , aromas and fragrances , enzymes , paints , disinfectants , diagnostics , ion exchange resins , adhesives , herbicides , pesticides , detergents .

Groups of substances in organic chemistry

There are two possibilities for a systematic classification of the individual substances in organic chemistry into groups of substances:

Classification according to functional group

Classification according to carbon structure

Cyclohexane , a saturated, cyclic aliphatic


See reaction mechanism

The reactions in organic chemistry can largely be classified into the following basic types:

In addition, many reactions are known by the name of their discoverer (see list of name reactions ).

A classification according to the type of bond or building block is found in the list of reactions in organic chemistry .

Organic analytical chemistry

Organic analytical chemistry deals with the investigation of organic substances. It can be about

  • Identify substances ( detection );
  • prove the presence or absence of impurities in substances (determination of purity );
  • to determine the proportions of substances in mixtures ( mixture );
  • to clarify the molecular structure of substances ( structure elucidation ).

Important methods for detection and purity determination ( qualitative analysis ) are classic wet chemical color and precipitate reactions, biochemical immunassay methods and a variety of chromatographic methods .

Determining the proportions in mixtures ( quantitative analysis ) is possible through wet chemical titrations with different endpoint displays, through biochemical immunoassay processes and through a large number of chromatographic processes as well as through spectroscopic methods, many of which are also used for structure elucidation, such as infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy ( NMR), Raman spectroscopy , UV spectroscopy . In addition to characteristic chemical reactions, X-ray diffraction analysis and mass spectrometry (MS) are used to determine the structure.


  • Carl Schorlemmer : Origin and Development of Organic Chemistry , Academic Publishing Company Geest & Portig, Leipzig, 1984.
  • H. Hart, LE Craine, DJ Hart, CM Hadad, N. Kindler: Organic Chemistry . 3rd edition Wiley-VCH, Weinheim 2007, ISBN 978-3-527-31801-8 .
  • KPC Vollhardt and NE Schore: Organic Chemistry . 4th edition, Wiley-VCH, Weinheim 2005, ISBN 978-3-527-31380-8 .
  • Heinz A. Staab: Hundred years of organic structural chemistry. Angewandte Chemie 70 (2), pp. 37-41 (1958), doi : 10.1002 / anie.19580700202 .
  • Joachim Buddrus: Fundamentals of Organic Chemistry , Walter de Gruyter, Berlin - New York, 3rd edition 2003, ISBN 978-3-11-014683-7 .
  • Hartmut Laatsch: The technique of organic separation analysis , Georg Thieme Verlag Stuttgart / New York 1988, ISBN 3-13-722801-8 .
  • dtv-atlas chemistry (Hans Breuer): Volume 2: Organic chemistry and plastics , 9th edition 2006, Deutscher Taschenbuch Verlag, ISBN 3-423-03218-9 .
  • RL Shriner, RC Fuson, DY Curtin, TC Morrill: The Systematic Identification of Organic Compounds - a laboratory manual 6th Edition, John Wiley & Sons New York / Chichester / Brisbane / Toronto 1980, ISBN 0-471-78874-0 .

Web links

Wikibooks: Organic Chemistry for Schoolchildren  - Learning and Teaching Materials
Wikibooks: Organic Chemistry  - Learning and Teaching Materials
Wiktionary: organic chemistry  - explanations of meanings, word origins, synonyms, translations
Commons : Organic Compound  - collection of images, videos, and audio files

Individual evidence

  1. Furni Novi Philosophici I, 1648-1650 Amsterdam, 66th
  2. Furni Novi Philosophici I, 1648-1650 Amsterdam, 77th
  3. Furni Novi Philosophici I, 1648-1650 Amsterdam, 99th
  4. Furni Novi Philosophici II, Amsterdam 1648-1650, 181st
  5. Furni Novi Philosophici II, Amsterdam 1648-1650, 71st
  6. Opera Chymica I, 50th
  7. Pogg. Ann. 31: 1-43 (1831).
  8. ^ Otto Westphal , Theodor Wieland , Heinrich Huebschmann: life regulator. Of hormones, vitamins, ferments and other active ingredients. Societäts-Verlag, Frankfurt am Main 1941 (= Frankfurter Bücher. Research and Life. Volume 1), p. 38.
  9. Gilberts Ann. 40 , 247.
  10. Ann. Chim.Phys. 24 , 264.
  11. Pogg. Ann. 12 , 253 (1828).
  12. Hermann Kolbe, About the natural connection between organic and inorganic compounds, the scientific basis for a natural classification of organic chemical bodies Ann. Chem. 113 , 1860, 293.
  13. Friedrich August Kekulé: About the paired compounds and the theory of polyatomic radicals . In: Liebigs Annalen der Chemie 104/2, 1857, pp. 129-256, doi : 10.1002 / jlac.18571040202
  14. Moritz Malischewski, K. Seppelt: The molecular structure of the pentagonal-pyramidal hexamethylbenzene dication in the crystal. In: Angewandte Chemie, 129, 2017, p. 374, doi : 10.1002 / anie.201608795 .
  15. Hans-Bernd Amecke: An overview of the chemical industry , pp. 74-75, VCH Verlagsgesellschaft mbH, Weinheim 1987, ISBN 3-527-26540-6 .
  16. European Commission: Eurostat .
  17. VCI: Brochures & Leaflets .
  18. ^ Hans-Bernd Amecke: Chemical Industry at a Glance, pp. 74-85, VCH Verlagsgesellschaft mbH, Weinheim 1987 ISBN 3-527-26540-6 .
  19. Hans-Bernd Amecke: Chemical Industry at a Glance, pp. 109–129, VCH Verlagsgesellschaft mbH, Weinheim 1987 ISBN 3-527-26540-6 .