The cyclobutane is a hydrocarbon consisting of a four-carbon cycloalkane, whose molecular formula is C4H8. It can also be called tetramethylene, considering that they are four CH unitstwo that make up a ring with square geometry, although the name cyclobutane is more accepted and known.
At room temperature it is a colorless, flammable gas that burns with a bright flame. Its most primitive use is as a source of heat when burning it; However, its structural base (the square) encompasses deep biological and chemical aspects, and collaborates in a certain way with the properties of these compounds..
The upper image shows a cyclobutane molecule with a square structure. In the next section, it will be explained why this conformation is unstable, since its links are tense..
After cyclopropane, it is the most unstable cycloalkane, since the smaller the ring size, the more reactive it will be. According to this, the cyclobutane is more unstable than the pentane and hexane cycles. However, it is curious to witness in its derivatives a nucleus or square heart, which, as will be seen, is dynamic.
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In the first image, the structure of cyclobutane was approached as a simple carbonized and hydrogenated square. However, in this perfect square the orbitals suffer a severe twist from their original angles: they are separated by an angle of 90º compared to 109.5º for a carbon atom with sp hybridization.3 (angular stress).
Carbon atoms sp3 they are tetrahedral, and for some tetrahedra it would be difficult to flex their orbitals so much to create a 90º angle; but it would be even more so for carbons with sp hybridizationstwo (120º) and sp (180º) deviate their original angles. For this reason cyclobutane has sp carbon atoms3 in essence.
Also, hydrogen atoms are very close to each other, eclipsed in space. This results in an increase in steric hindrance, which weakens the supposed square due to its high torsional stress..
Therefore, angular and torsional stresses (encapsulated in the term 'ring stress') make this conformation unstable under normal conditions..
The cyclobutane molecule will seek to reduce both stresses, and to achieve this it adopts what is known as the butterfly or puckered conformation..
The true conformations of cyclobutane are shown above. In them the angular and torsional stresses decrease; since, as can be seen, now not all hydrogen atoms are eclipsed. However, there is an energy cost: the angle of its links is sharpened, that is, it falls from 90 to 88º.
Note that it can be compared to a butterfly, whose triangular wings are made up of three carbon atoms; and the fourth, positioned at an angle of 25º with respect to each wing. The two-way arrows indicate that there is an equilibrium between both conformers. It is as if the butterfly went down and raised its wings.
In cyclobutane derivatives, on the other hand, this flapping would be expected to be much slower and spatially impeded..
Suppose you forget the squares for a moment, and they are replaced by carbonated butterflies instead. These in their flapping can only be held together in the liquid by London dispersion forces, which are proportional to the area of their wings and their molecular mass..
Colorless gas.
56.107 g / mol.
12.6 ° C. Therefore, in cold conditions it could be handled in principle like any liquid; with the only detail, that it would be highly volatile, and its vapors would still represent a risk to be taken into account.
-91ºC.
50ºC closed glass.
Insoluble in water, which is not surprising given its nonpolar nature; but, it is slightly soluble in alcohols, ether, and acetone, which are less polar solvents. It is expected to be soluble (although not reported) logically in apolar solvents such as carbon tetrachloride, benzene, xylene, etc..
0.7125 at 5ºC (in relation to 1 of the water).
1.93 (in relation to 1 of the air). This means that it is denser than air, and therefore, unless there are currents, its tendency will not be to rise..
1,180 mmHg at 25ºC.
1.3625 at 290ºC.
-655.9 kJ / mol.
6.6 Kcal / mol at 25ºC.
Cyclobutane is synthesized by hydrogenation of cyclobutadiene, whose structure is almost the same, with the only difference that it has a double bond; and therefore it is even more reactive. This is perhaps the simplest synthetic route to obtain it, or at least solely to it and not to a derivative.
In crude oil it is unlikely to obtain it since it would end up reacting in such a way as to break the ring and form the line chain, that is, n-butane.
Another method to obtain cyclobutane consists in striking ultraviolet radiation on the ethylene molecules, CHtwo= CHtwo, which dimerize. This reaction is favored photochemically, but not thermodynamically:
The image above summarizes very well what was said in the paragraph above. If instead of ethylene one had, for example, any two alkenes, a substituted cyclobutane would be obtained; or what is the same, a derivative of cyclobutane. In fact, many derivatives with interesting structures have been synthesized by this method..
Other derivatives, however, involve a series of complicated synthetic steps. Therefore, cyclobutanes (as their derivatives are called) are the object of study for organic syntheses..
Cyclobutane alone has no other use than to serve as a heat source; but, its derivatives, enter intricate terrain in organic synthesis, with applications in pharmacology, biotechnology and medicine. Without delving into overly complex structures, penitrems and grandisol are examples of cyclobutanes.
Cyclobutanes generally have properties that are beneficial for the metabolisms of bacteria, plants, marine invertebrates, and fungi. They are biologically active, and that is why their uses are very varied and difficult to specify, since each one has its particular effect on certain organisms..
Grandisol, for example, is a pheromone from the weevil (a type of beetle). Above, and finally, its structure is shown, considered a monoterpene with a square base of cyclobutane.
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