The chemical formula of glycerin. Structural and molecular formula

The simplest polyhydric alcohol, in which there are 3 OH groups, is glycerol. The formula common for compounds of this type is CnH2n-1 (OH) 3. In order to better understand the properties and application of glycerin and its homologues, let us consider the types of substance formulas, each of which is used in certain situations.

Classification and nomenclature of glycerol

In organic chemistry, alcohols are substances derived from hydrocarbons. Some of the hydrogen atoms in the molecules are replaced by one or more hydroxy groups. Alcohols differ in the number of OH-groups (single-, double-, polyatomic). The lowest representatives of the class with the number of carbon atoms from 1 to 12 are liquid substances, the higher ones are solids. Alkantriols, or glycerols - are triatomic alcohols containing in their composition three hydroxyls bound to three different carbon atoms. The 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 propanetriol-1,2,3 (a synonym is glycerin). The formula for the substance is C ₃ H ₈ O ₃ . The systematic nomenclature presupposes the mention of the name of the corresponding alkane with the word "triol", the use of Arabic numerals determining the position of the OH group. Numbering in molecules of homologs of glycerin is from the nearest to the end of the chain of hydroxyl. Possible types of isomerism: the structure of the carbon chain, the position of hydroxy groups, optical.

The discovery of glycerol

The Swedish pharmacist K. Scheele in 1779 when saponifying fats for the first time received a new syrupy substance. In 33 years the Frenchman M. Shevrel called the sweet liquid glycerin.

Chemical composition was established by Peluz in 1836. A significant contribution to the study of the structure was made by Berthelot (1854) and Wurz (1857), who continued to investigate glycerin. The molecular formula and the nature of the radical allowed the attribution of glycerin to the ultimate alcohols.

The need for glycerol increased significantly after 1847, when the nitric acid ester was discovered. Swedish engineer A. Nobel in 1875 was able to get with the help of glycerin explosive - dynamite.

The composition, structure and simplest formula of glycerol

The simplest record of the composition of matter coincides with the true, empirical and gross formula of glycerin - C ₃ H ₈ O ₃ . The carbon chain has 3 atoms, each of which is linked to the hydroxy group. Chemical symbols denote the constituent atoms of the atom: C - carbon, O - oxygen, H - hydrogen. The composition of glycerin reflects different formulas (molecular, structural). Sharoenergetic and hemispherical models are widely used in the study of matter. Two-dimensional and three-dimensional structures created by computer simulation are spatial images of a molecule of glycerin. They allow us to visualize the composition, mutual arrangement and distance, the angle of the bond between atoms.

Molecular and molar masses of glycerin

According to the formula, you can find the molecular and molar masses, the percentage of elements in the substance. For calculations it is necessary to use the atomic masses of the elements indicated in the periodic table. The empirical formula of glycerin: C ₃ H ₅ (OH) ₃ . By multiplying the atomic mass (in ae m) of each element by the number of atoms, and then adding the values obtained, we find the molecular (Mr) and molar (M) masses. For the type of calculations it is more convenient to use the gross formula of glycerin - C ₃ H ₈ O ₃ .

• Ar (H) = 1.00794; The number of atoms in the molecule is 8.
• Ar (C) = 12,0107; Atoms - 3.
• Ar (O) = 15.9994; Atoms - 3.
• Mr (C ₃ H ₈ O ₃ ) = 12.0107 * 3 + 1.00794 * 8 + 15.9994 * 3 = 92.09382 a. eat.
• M (C ₃ H ₈ O ₃ ) = 92.09382 g / mol /
• The percentage of elements in the molecule of the substance: H - 8,756%, C - 39,125%, O - 52,119%.

Rational and structural formula of glycerin

The composition of the substance and its molecules reflect a rational and gross formula, but they do not give an idea of the arrangement of the atoms that glycerin is different from. The formula structural and computer model are better suited for studying the structure of the molecule, the bonds between atoms.

• The rational formula of glycerin is C ₃ H ₅ (OH) ₃ . From the composition of the molecule, functional groups OH are separated and enclosed in parentheses. Immediately behind the closing bracket is the number of hydroxy groups in the molecule.
• A semi-expanded form of the rational formula is HOCH ₂ CH (OH) CH ₂ OH (glycerol).
• The structural formula in graphic form shows the arrangement of the molecule. Dashes between atoms symbolize chemical bonds.
• The Lewis structure contains points denoting valence electrons and couples participating in bond formation.

Some kinds of images of a molecule take up a lot of space, therefore, abbreviated formulas, for example, HOCH ₂ -CHOH-CH ₂ OH, are more often used, as well as skeletal structures:

State of atoms in the molecule of glycerin

Hydroxyl is a polar particle, besides, oxygen has an unshared pair of electrons. The presence of three hydroxy groups leads to further polarization of the O-H bond. A partial charge of "+" appears on the carbon atoms, facilitating the nucleophilic substitution of hydroxyl. Features of 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 acid properties, compared to ethanol and propanol. Among the most important derivatives is glycerol trioleate. Formula:

• The simplest is C ₅₇ H ₁₀₄ O ₆ ;
• Semi-unfolded rational - (C ₁₇ H ₃₃ SO ₃ ) ₃ C ₃ H ₅ ;
• Rational with elements of structural and skeletal -

Appearance of glycerin

At room temperature, propanetriol-1,2,3 is a colorless or pale yellow liquid, odorless, sweet to taste. The glycerin, hardened at low temperatures, melts at a temperature of 17.8 ° C. The boiling point of the substance with subsequent evaporation begins at 290 ° C. Glycerin is slightly heavier than water, calculating its density at 20 ° C gives a value of 1.2604 g / cm3.

Properties of propanthriol-1,2,3

The chemical formula of glycerin does not give an idea of the amphoteric character of the compound. Weak acidic and basic properties of substances are associated with the peculiarities of the influence of atoms in the molecule, polarization in the O-H group. In the presence of alkali glycerol interacts with copper (II) hydroxide , a blue-colored complex (one of the qualitative reactions) is obtained . With acids, the reaction of glycerol is completed by the formation of esters. Interaction of a triatomic alcohol with nitric acid in the presence of H ₂ SO ₄ (conc.) Leads to the formation of nitroglycerin.

At home, fats and oils are obtained with glycerine, ethyl alcohol, and other ingredients. The process of preparation requires careful heating of the mass in a water bath, a creative attitude to the selection of components and forms for the finished soap product.

Glycerin and its derivatives are used in enamels, paints, many medicines, toiletries. A sweet substance is found in a variety of foods, including bakery products. International name of sweetener and confectionery flavors - E422. Along with other alcohols, as well as esters of fatty acids, glycerol is considered as a potential replacement of fuel derived from petroleum. Economical methods of using new varieties of biodiesel to fuel cars will revolutionize the world's transport economy. The ecological situation will significantly improve, the dependence of the world economy on oil and gas production will decrease.