The simplest polyhydric alcohol in whichThere are 3 OH groups, - glycerin. The formula, common for compounds of this type, is CnH2n - 1 (OH) 3. To better understand the properties and use of glycerol and its homologues, consider the types of formulas of the substance, each of which is used in certain situations.
Classification and nomenclature of glycerols
In organic chemistry, alcohols are substances thatderived from hydrocarbons. Part of the hydrogen atoms in the molecules is replaced by one or more hydroxy groups. Alcohols differ in the number of OH groups (mono-, di-, and polyatomic). The lowest members of the class with the number of carbon atoms from 1 to 12 are liquid substances, the highest are solid bodies. Alkantrioles, or glycerols, are trihydric alcohols containing three hydroxyls associated with three different carbon atoms. Compounds belonging to this group exhibit amphoteric properties due to the mutual influence of the hydroxy group and the radical.
The simplest representative of alkantriols is propantriol-1,2,3 (synonym - glycerin). Formula - C3X8ABOUT3. Systematic nomenclature impliesmention of the name of the corresponding alkane with the word "triol", the use of Arabic numerals, which determine the position of the OH-group. The numbering in the molecules of homologues of glycerol is from the hydroxyl nearest to the end of the chain. Possible types of isomerism: the structure of the carbon chain, the position of hydroxy groups, optical.
The discovery of glycerol
Swedish pharmacist K. Scheele in 1779, when saponifying fats, first received a new syrupy substance. After 33 years, the Frenchman M. Chevrel called the sweet liquid glycerin.
The chemical composition was established by Pelouse in 1836.A significant contribution to the study of the structure was made by Berthelot (1854) and Würz (1857), who continued to investigate glycerin. The molecular formula and nature of the radical made it possible to classify glycerol as the ultimate alcohol.
The need for glycerol has increased significantlyafter 1847, when the ester of nitric acid was discovered. The Swedish engineer A. Nobel in 1875 managed to get explosives with the help of glycerin - dynamite.
The composition, structure and simple formula of glycerin
The simplest record of the composition of the substance coincides with the true, empirical and gross formula of glycerin - C3X8ABOUT3. The carbon chain has 3 atoms, each ofthey are linked to the hydroxy group. Chemical symbols denote the constituent atoms: C - carbon, O - oxygen, H - hydrogen. The composition of glycerin reflect different formulas (molecular, structural). Widely used in the study of substances are ball-bearing and hemispherical models. Two-dimensional and three-dimensional structures created using computer simulation are spatial images of the glycerol molecule. They allow you to visualize the composition, mutual placement and distance, the angle of the bond between the atoms.
Molecular and Molar Mass of Glycerin
According to the formula can be found molecular and molarmass, the percentage of elements in the substance. For calculations it is necessary to use the values of the atomic masses of the elements specified in the periodic table. Empirical glycerin formula: C3X5(Oh)3. By multiplying the atomic mass (in a. E. M.) of each element on the number of atoms with the subsequent addition of the obtained values, we find the molecular (Mr) and molar (M) masses. For this type of calculation, it is more convenient to use the glycerin gross formula - C3X8ABOUT3.
- Ar (H) = 1.00794; the number of atoms in a molecule is 8.
- Ar (C) = 12.0107; atoms - 3.
- Ar (O) = 15.9994; atoms - 3.
- Mr (C3H8ABOUT3) = 12,0107 * 3 + 1,00794 * 8 + 15.9994 * 3 = 92,09382 a. eat.
- M (S3H8ABOUT3) = 92,09382 g / mol /
- The percentage of elements in the substance molecule: H - 8.756%, C - 39.125%, O - 52.119%.
Rational and structural formula of glycerin
The composition of the substance and its molecules reflectrational and gross formula, but they do not give an idea about the arrangement of atoms, which is different glycerol. Formula structural and computer models are better suited for studying the structure of the molecule, the bonds between atoms.
- Rational glycerin formula - C3X5(Oh)3 . From the composition of the molecule, the functional groups of OH are isolated and enclosed in parentheses. Immediately after the closing bracket, the number of hydroxy groups in the molecule is indicated.
- Half-open view of a rational formula - HOCH2CH (OH) CH2OH (glycerin).
- The structural formula graphically shows the location of the molecule. Dashes between atoms symbolize chemical bonds.
- The Lewis structure contains points that denote valence electrons and pairs involved in bonding.
Some types of molecule images take up a lot of space; therefore, abbreviated formulas are used more often, for example, SOCL2—CHON — CH2HE, as well as skeletal structures:
The state of the atoms in the glycerol molecule
Hydroxyl - a polar particle, besides oxygenpossesses a lonely pair of electrons. The presence of three hydroxy groups leads to further polarization of the O – H bond. A partial charge of “+” appears on carbon atoms, facilitating nucleophilic substitution of hydroxyl. Features of the composition and structure, which reflects the structural formula of glycerin, are confirmed in the properties of the substance. This compound is characterized by numerous hydrogen bridges - weak additional bonds. Glycerin has more pronounced properties of the acid in comparison with ethanol and propanol. Among the most important derivatives is glycerol trioleate. Formula:
- simplest - With57H104ABOUT6;
- semi-expanded rational - (C17H33COO)3FROM3H5;
- rational with elements of structural and skeletal -
Appearance of glycerin
At room temperature, propantriol-1,2,3 -colorless or pale yellow liquid, odorless, sweet in taste. The glycerin hardened at low temperatures melts at a temperature of 17.8 ° C. Boiling of the substance with subsequent evaporation begins at 290 ° C. Glycerin is slightly heavier than water, the calculation of its density at 20 ° C gives a value of 1.2604 g / cm3.
Properties of propantriol-1,2,3
The chemical formula of glycerin does not giveideas about the amphoteric nature of the compound. Weak acid and basic properties of substances are associated with the peculiarities of the influence of atoms in a molecule, polarization in the O – H group. In the presence of alkali, glycerin interacts with copper (II) hydroxide, a blue-dyed complex is obtained (one of the qualitative reactions). With acids, the reaction of glycerol is completed by the formation of esters. The interaction of triatomic alcohol with nitric acid in the presence of H2CO4 (conc.) leads to the formation of nitroglycerin.
At home from fats and oils usingglycerin, ethyl alcohol, other ingredients receive soap. The preparation process requires careful heating of the mass in a water bath, creative attitude to the selection of components and forms for the finished product soap making.
Glycerin and its derivatives are used in enamels,paints, many medicines, toiletries. Contains a sweet substance in a variety of food products, including bakery products. The international name of the sugar substitute and confectionery flavor is E422. Along with other alcohols, as well as fatty acid esters, glycerin is considered as a potential substitute for fuels derived from petroleum. Economical methods of using new types of biodiesel for refueling cars will revolutionize the global transport industry. The ecological situation will significantly improve, the dependence of the world economy on oil and gas production will decrease.
