Cyclohexane is a cycloalkane with the molecular formula C6H12. Cyclohexane is a colourless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products. Cyclohexane is used for the industrial production of adipic acid and caprolactam, which are precursors to nylon. Cyclohexyl is abbreviated Cy. On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst. Producers of cyclohexane account for 11.4% of global demand for benzene. The reaction is exothermic, with ΔH = -216.37 kJ/mol). Dehydrogenation commenced noticeably above 300 °C, reflecting the favorable entropy for dehydrogenation. Unlike benzene, cyclohexane is not found in natural resources such as coal. For this reason, early investigators synthesized their cyclohexane samples. In 1867 Marcellin Berthelot reduced benzene with hydroiodic acid at elevated temperatures. In 1870, Adolf von Baeyer repeated the reaction and pronounced the same reaction product "hexahydrobenzene" in 1890 Vladimir Markovnikov believed he was able to distill the same compound from Caucasus petroleum, calling his concoction "hexanaphtene".
Their cyclohexanes boiled higher by 10 °C than either hexahydrobenzene or hexanaphtene, but this riddle was solved in 1895 by Markovnikov, N. M. Kishner, Nikolay Zelinsky when they reassigned "hexahydrobenzene" and "hexanaphtene" as methylcyclopentane, the result of an unexpected rearrangement reaction. In 1894, Baeyer synthesized cyclohexane starting with a ketonization of pimelic acid followed by multiple reductions: In the same year, E. Haworth and W. H. Perkin Jr. prepared it via a Wurtz reaction of 1,6-dibromohexane. Although rather unreactive, cyclohexane undergoes catalytic oxidation to produce cyclohexanone and cyclohexanol; the cyclohexanone–cyclohexanol mixture, called "KA oil", is a raw material for adipic acid and caprolactam, precursors to nylon. Several million kilograms of cyclohexanone and cyclohexanol are produced annually, it is used as a solvent in some brands of correction fluid. Cyclohexane is sometimes used as a non-polar organic solvent, although n-hexane is more used for this purpose.
It is used as a recrystallization solvent, as many organic compounds exhibit good solubility in hot cyclohexane and poor solubility at low temperatures. Cyclohexane is used for calibration of differential scanning calorimetry instruments, because of a convenient crystal-crystal transition at −87.1 °C. Cyclohexane vapour is used in heat treating equipment manufacture; the 6-vertex edge ring does not conform to the shape of a perfect hexagon. The conformation of a flat 2D planar hexagon has considerable angle strain because its bonds are not 109.5 degrees. Therefore, to reduce torsional strain, cyclohexane adopts a three-dimensional structure known as the chair conformation, which interconvert at room temperature via a process known as a chair flip. During the chair flip, there are three other intermediate conformations that are encountered: the half-chair, the most unstable conformation, the more stable boat conformation, the twist-boat, more stable than the boat but still much less stable than the chair.
The chair and twist-boat are energy minima and are therefore conformers, while the half-chair and the boat are transition states and represent energy maxima. The idea that the chair conformation is the most stable structure for cyclohexane was first proposed as early as 1890 by Hermann Sachse, but only gained widespread acceptance much later; the new conformation puts the carbons at an angle of 109.5°. Half of the hydrogens are in the plane of the ring while the other half are perpendicular to the plane; this conformation allows for the most stable structure of cyclohexane. Another conformation of cyclohexane exists, known as boat conformation, but it interconverts to the more stable chair formation. If cyclohexane is mono-substituted with a large substituent the substituent will most be found attached in an equatorial position, as this is the more stable conformation. Cyclohexane has the lowest torsional strain of all the cycloalkanes. Cyclohexane has two crystalline phases; the high-temperature phase I, stable between 186 K and the melting point 280 K, is a plastic crystal, which means the molecules retain some rotational degree of freedom.
The low-temperature phase II is ordered. Two other low-temperature phases III and IV have been obtained by application of moderate pressures above 30 MPa, where phase IV appears in deuterated cyclohexane. Here Z is the number structure units per unit cell; the Flixborough disaster, a major industrial accident caused by an explosion of cyclohexane. Hexane Ring flip Cyclohexane International Chemical Safety Card 0242 National Pollutant Inventory – Cyclohexane fact sheet NIOSH Pocket Guide to Chemical Hazards Cyclohexane@3Dchem Hermann Sachse and the first suggestion of a chair conformation. NLM Hazardous Substances Databank – Cyclohexane Methanol Discovered in Space Calculation of vapor pressure, liquid density, dynamic liquid viscosity, surface tension of cyclohexane Cyclohexane production process flowsheet, benzene hydrogenation technique
Meine Oma fährt im Hühnerstall Motorrad in a German humouristic song. It dates back to the 1930s stemming from two older works: the refrain of the Rheinländer dance Wir versaufen unsrer Oma ihr klein Häuschen, authored by Robert Steidl in 1922, constitutes most of the melody, while the text is a variation of the Foxtrott Meine Oma fährt Motorrad, ohne Bremse, ohne Licht, a 1928 work with words by Ernst Albert and music by Erwin Bolt; the Deutsches Volksliedarchiv have conducted extensive research into the origin of the song. They describe it as "an instance of absurd humour, as well as a typical example of the songs that developed in parallel to the media musical culture of the 20th century mutating under their own dynamic." When the two works mixed is not known. The earliest known instance is an incipit in a magazine containing the words of the song in 1935 or 1936; the earliest document held by the Deutschen Volksliedarchiv dates from 1942. In 1958, Meine Oma fährt im Hühnerstall Motorrad was printed for the first time in a songbook, Der Zündschlüssel, by the Fidula-Verlag printing company, from the recollection of editor Johannes Holzmeister.
1. Meine Oma fährt im Hühnerstall Motorrad, Motorrad,meine Oma fährt im Hühnerstall Motorrad, meine Oma ist ’ne ganz patente Frau. 2. Meine Oma hat im hohlen Zahn ein Radio … 3. Meine Oma hat ’nen Nachttopf mit Beleuchtung … 4. Meine Oma hat ’ne Glatze mit Geländer … 5. Meine Oma hat ’ne Brille mit Gardinen … 6. Meine Oma hat ’nen Peticoat aus Wellblech … 7. Meine Oma hat im Strumpfband ’nen Revolver … 8. Denn meine Oma spielt in Hollywood ’nen Cowboy … In 1980, Fredrik Vahle published a 25-stanza version in Liederspatz, where the grandma sits behind the wheel, watches the TV series Tagesschau, goes to the disco. In 2019, Westdeutscher Rundfunk Köln had a new version sung by the children choir of the Choral Academy of Dortmund, authored by one of the hosts of WDR-2 as a caricature of intergenerational tensions; the new version appeared on 27 December 2019 on an online video. The file was removed shortly thereafter, following criticism of the refrain that states "My grand-mother is an old environmental pig".
However, the video remains available from YouTube. The next day, in a special broadcast on WDR, Tom Buhrow and the head of programmes Jochen Rausch apologised without reserve for the video, which he called a "mistake"; the choir director, Zeljo Davutovic, issued a statement praising the youth movement Fridays for Future, commenting "this is not about grand-mothers, this is about all of us". On 29 December, Right-Wing groups started demonstrating in front of the redaction of WDR in protest of the song. Counter-protests by Left-Wing groups soon followed, as well as a police presence. In total, around 100 people were involved. Christoph Meinel. "Von Holzauktionen, Kobolden und modernen Omas". Forschungsstelle für fränkische Volksmusik. Retrieved 2018-06-17. Xaver Frühbeis: Ohne Bremse, ohne Licht: "Meine Oma fährt im Hühnerstall Motorrad". BR-Klassik Mittagsmusik extra, 31. Dezember 2010, abgerufen am 17. Juni 2018
Experimental evolution is the use of laboratory experiments or controlled field manipulations to explore evolutionary dynamics. Evolution may be observed in the laboratory as individuals/populations adapt to new environmental conditions by natural selection. There are two different ways. One is via an individual organism gaining a novel beneficial mutation; the other is from allele frequency change in standing genetic variation present in a population of organisms. Other evolutionary forces outside of mutation and natural selection can play a role or be incorporated into experimental evolution studies, such as genetic drift and gene flow; the organism used is decided by the experimenter, based on whether the hypothesis to be tested involves adaptation through mutation or allele frequency change. Many generations are required for adaptive mutation to occur, experimental evolution via mutation is carried out in viruses or unicellular organisms with rapid generation times, such as bacteria and asexual clonal yeast.
Polymorphic populations of asexual or sexual yeast, multicellular eukaryotes like Drosophila, can adapt to new environments through allele frequency change in standing genetic variation. Organisms with longer generations times, although costly, can be used in experimental evolution. Laboratory studies with foxes and with rodents have shown that notable adaptations can occur within as few as 10–20 generations and experiments with wild guppies have observed adaptations within comparable numbers of generations. More experimentally evolved individuals or populations are analyzed using whole genome sequencing, an approach known as Evolve and Resequence. E&R can identify mutations that lead to adaptation in clonal individuals or identify alleles that changed in frequency in polymorphic populations, by comparing the sequences of individuals/populations before and after adaptation; the sequence data makes it possible to pinpoint the site in a DNA sequence that a mutation/allele frequency change occurred to bring about adaptation.
The nature of the adaptation and functional follow up studies can shed insight into what effect the mutation/allele has on phenotype. Unwittingly, humans have carried out evolution experiments for as long as they have been domesticating plants and animals. Selective breeding of plants and animals has led to varieties that differ from their original wild-type ancestors. Examples are maize, or the large number of different dog breeds; the power of human breeding to create varieties with extreme differences from a single species was recognized by Charles Darwin. In fact, he started out his book The Origin of Species with a chapter on variation in domestic animals. In this chapter, Darwin discussed in particular the pigeon. Altogether at least a score of pigeons might be chosen, which if shown to an ornithologist, he were told that they were wild birds, would I think, be ranked by him as well-defined species. Moreover, I do not believe that any ornithologist would place the English carrier, the short-faced tumbler, the runt, the barb and fantail in the same genus.
I am convinced that the common opinion of naturalists is correct, that all have descended from the rock-pigeon, including under this term several geographical races or sub-species, which differ from each other in the most trifling respects. One of the first to carry out a controlled evolution experiment was William Dallinger. In the late 19th century, he cultivated small unicellular organisms in a custom-built incubator over a time period of seven years. Dallinger increased the temperature of the incubator from an initial 60 °F up to 158 °F; the early cultures had shown clear signs of distress at a temperature of 73 °F, were not capable of surviving at 158 °F. The organisms Dallinger had in his incubator at the end of the experiment, on the other hand, were fine at 158 °F. However, these organisms would no longer grow at the initial 60 °F. Dallinger concluded that he had found evidence for Darwinian adaptation in his incubator, that the organisms had adapted to live in a high-temperature environment.
Dallinger's incubator was accidentally destroyed in 1886, Dallinger could not continue this line of research. From the 1880s to 1980, experimental evolution was intermittently practiced by a variety of evolutionary biologists, including the influential Theodosius Dobzhansky. Like other experimental research in evolutionary biology during this period, much of this work lacked extensive replication and was carried out only for short periods of evolutionary time. Experimental evolution has been used in various formats to understand underlying evolutionary processes in a controlled system. Experimental evolution has been performed on multicellular and unicellular eukaryotes and viruses. Similar works have been performed by directed evolution of individual enzyme and replicator genes. In the 1950s, the Soviet biologist Georgy Shaposhnikov conducted experiments on aphids of the Dysaphis genus. By transferring them to plants nearly or unsuitable for them, he had forced populations of parthenogenetic descendants to adapt to the new food source to the point of reproductive isolation from the regular populations of the same species.
One of the first of a new wave of experiments using this strategy was the laboratory "evolutionary radiation" of Drosophila melanogaster populations that Michael R. Rose started in February, 1980; this system started