There is such a compound: tartaric acid. It is a waste product of the wine industry. Initially, tartaric acid is found in grape juice in the form of its acidic sodium s alt. However, during the fermentation process, sugar under the action of special yeast turns into alcohol, and from this the solubility of the tartaric acid s alt decreases. Then it precipitates, which is called tartar. It is crystallized, acidified and, in the end, the acid itself is obtained. However, things are not so simple with her.
Pasteur
In fact, the solution contains two acids: tartaric and another, grape. They differ in that tartaric acid has optical activity (rotates the plane of polarized light to the right), while grape acid does not. Louis Pasteur investigated this phenomenon and found that the crystals formed by each of the acids are mirror images of each other, that is, he suggested a connection between the shape of the crystals and the optical activity of substances. In 1848, after a series of experiments, he announced a new type of isomerism of tartaric acids, which he called enantiomerism.
Vant Hoff
Jacob van't Hoff introduced the concept of the so-called asymmetric (or chiral) carbon atom. This is the carbon that is bonded to four different atoms in an organic molecule. For example, in tartaric acid, the second atom in the chain has a carboxyl group in its neighbors,hydrogen, oxygen and a second piece of tartaric acid. Since in this configuration carbon arranges its bonds in the form of a tetrahedron, it is possible to obtain two compounds that will be mirror images of each other, but it will be impossible to "superpose" them one on top of the other without changing the order of bonds in the molecule. By the way, this way to define chirality is Lord Kelvin's suggestion: the display of a group of points (in our case, points are atoms in a molecule) that have chirality in an ideal flat mirror cannot be combined with the group of points itself.
Symmetry of molecules
The mirror explanation looks simple and beautiful, but in modern organic chemistry, where really huge molecules are studied, this speculative method is associated with significant difficulties. So they turn to mathematics. Or rather, symmetry. There are so-called symmetry elements - axis, plane. We twist-twist the molecule, leaving the symmetry element fixed, and the molecule, after turning through a certain angle (360°, 180°, or something else), begins to look exactly the same as at the beginning.
And the very asymmetric carbon atom introduced by van't Hoff is the basis of the simplest kind of symmetry. This atom is the chiral center of the molecule. It is tetrahedral: it has four bonds with different substituents on each. And therefore, turning the connection along the axis containing such an atom, we will get an identical picture only after a full rotation of 360 °.
In general, the chiral center of a molecule can be not only oneatom. For example, there is such an interesting compound - adamantane. It looks like a tetrahedron, in which each edge is additionally bent outward, and in each corner there is a carbon atom. The tetrahedron is symmetrical about its center, and so is the adamantane molecule. And if four different substituents are added to four identical "nodes" of adamantane, then it will also acquire point symmetry. After all, if you rotate it relative to its internal "center of gravity", the picture will coincide with the initial one only after 360 °. Here, instead of an asymmetric atom, the role of the chiral center is played by the "empty" adamantane center.
Stereoisomers in bioorganic compounds
Chirality is an extremely important property for biologically active compounds. Only isomers with a certain structure participate in the processes of vital activity. And almost all substances significant for the body are arranged in such a way that they have at least one chiral center. The most popular example is sugar. That's glucose. There are six carbon atoms in its chain. Of these, four atoms have four different substituents next to them. This means that there are 16 possible optical isomers for glucose. All of them are divided into two large groups according to the configuration of the asymmetric carbon atom closest to the alcohol group: D-saccharides and L-saccharides. Only D-saccharides are involved in metabolic processes in a living organism.
Also a fairly common example for stereoisomerism in bioorganic chemistry is amino acids. All naturalamino acids have amino groups near the carbon atom closest to the carboxyl group. Thus, in any amino acid, this atom will be asymmetric (various substituents - carboxyl group, amino group, hydrogen and the rest of the chain; the exception is glycine with two hydrogen atoms).
Accordingly, according to the configuration of this atom, all amino acids are also divided into D-series and L-series, only in natural processes, unlike sugars, the L-series predominates.
