Structural and molecular formula: acetylene

Features of the structure of acetylene affect its properties, production and application. The conventional designation of the substance - C₂H₂ Is its simplest and gross formula. Acetylene is formed by two carbon atoms, between which there is a triple bond. Its presence reflects different types of formulas and models of the ethylene molecule, allowing to understand the problem of the influence of the structure on the properties of matter.

Alkines. The general formula. Acetylene

Alkyl hydrocarbons, or acetylene, areacyclic, unsaturated. The chain of carbon atoms is not closed, there are simple and multiple bonds in it. The composition of alkynes reflects the summary formula C_nH_2n _{- 2}. In the molecules of substances of this class there isone or more triple bonds. Acetylene compounds refer to unsaturated compounds. This means that only one valence of carbon is realized due to hydrogen. The remaining three bonds are used when interacting with other carbon atoms.

The first - and the most famous representativealkynes-acetylene, or ethyne. The trivial name of the substance comes from the Latin word "acetum" - "vinegar" and Greek - "hyle" - "tree". The founder of the homologous series was discovered in 1836 in chemical experiments, later the substance was synthesized from coal and hydrogen by E. Davy and M. Bertlo (1862). At normal temperature and normal atmospheric pressure, acetylene is in a gaseous state. It is a colorless gas, odorless, slightly soluble in water. Ethin is more readily soluble in ethanol and acetone.

Molecular formula of acetylene

Etin - the simplest member of its homologous series, its composition and structure reflect the formulas:

FROM₂H₂ - molecular recording of the composition of ethane, which givesthe notion that a substance is formed by two carbon atoms and the same number of hydrogen atoms. According to this formula, the molecular and molar masses of the compound can be calculated. Mr (From₂H₂) = 26 a. e. m., M (C₂H₂) = 26.04 g / mol.
Н: С ::: С: Н - the electron-dot formula of acetylene. Similar images, called "Lewis structures," reflect the electronic structure of the molecule. When writing it is necessary to observe the rules: the hydrogen atom tends to have the configuration of the valence shell of helium in the formation of a chemical bond, the other elements - by an octet of external electrons. Each colon means a common for the two atoms or an unshared pair of electrons of the external energy level.
H-C≡C-H is the structural formula of acetylene, which reflects the order and multiplicity of bonds between atoms. One dash replaces one pair of electrons.

Models of the acetylene molecule

Formulas showing the distribution of electrons,served as a foundation for the creation of atomic-orbital models, spatial formulas of molecules (stereochemical). As early as the end of the 18th century, spherical rod models became widespread - for example, balls of different color and size, designating carbon and hydrogen, which form acetylene. The structural formula of a molecule is represented in the form of rods, which symbolize the chemical bonds and their number in each atom.

The spherical model of acetylene reproducesvalence angles equal to 180 °, but the internuclear distances in the molecule are reflected approximately. The voids between the balls do not create a picture of the filling of the space of atoms with electron density. The drawback is eliminated in the models of Driding, which designate the nuclei of atoms not with balls, but with the points of attachment of the rods to each other. Modern volumetric models give a more vivid idea of atomic and molecular orbitals.

Hybrid atomic orbitals of acetylene

The carbon in the excited state contains three p-orbitals and one s with unpaired electrons. In the formation of methane (CH₄₎ they take part in the creation of equivalentbonds with hydrogen atoms. The famous American researcher L. Pauling developed the theory of the hybrid state of atomic orbitals (AO). The explanation of the behavior of carbon in chemical reactions is the alignment of AO in form and energy, the formation of new clouds. Hybrid orbitals give stronger connections, the formula becomes more stable.

Atoms of carbon in the acetylene molecule, in contrast tomethane, undergo sp-hybridization. S and p electrons are mixed in shape and energy. Two sp-orbitals appear, lying at an angle of 180 °, directed on opposite sides of the nucleus.

Triple connection

In acetylene hybrid electronic clouds of carbonparticipate in the creation of σ-bonds with the same neighboring atoms and with hydrogen in CH-pairs. There remain two non-hybrid p-orbitals perpendicular to each other. In the ethylene molecule, they participate in the formation of two π-bonds. Together with σ there is a triple bond, which reflects the structural formula. Acetylene differs from ethane and ethylene by the distance between atoms. The triple bond is shorter than the double, but has a greater energy reserve, is more solid. The maximum density of σ- and π-bonds is located in perpendicular regions, which leads to the formation of a cylindrical electron cloud.

Features of the chemical bond in acetylene

Ethylene molecule has a linear form, which is successfulreflects the chemical formula of acetylene - H-C≡C-H. The carbon and hydrogen atoms are along a straight line, between them there are 3 σ- and 2 π-bonds. Free movement, rotation along the axis C-C is impossible, this is prevented by the presence of multiple bonds. Other features of the triple bond:

the number of pairs of electrons connecting two carbon atoms is 3;
length - 0.120 nm;
The energy of rupture is 836 kJ / mol.

For comparison: in ethane and ethylene molecules, the length of the single and double chemical bonds is 1.54 and 1.34 nm, respectively, the energy of the C-C rupture is 348 kJ / mol, C = C-614 kJ / mol.

Homologues of acetylene

Acetylene is the simplest representative of alkynes, whose molecules also have a triple bond. Propyn CH₃С≡СН - homologue of acetylene. Formula of the third representative of alkynes - butyne-1 - CH₃CH₂С≡СН. Acetylene is the trivial name of ethane. The systematic nomenclature of alkynes is subject to IUPAC rules:

in linear molecules, the name of the main chain, which arises from the Greek numeral, is added to which the suffix -in and the number of the atom are added with a triple bond, for example, ethyne, propyne, butyn-1;
the numbering of the main chain of atoms begins at the end of the molecule closest to the triple bond;
for branched hydrocarbons, the name of the lateral branch is first followed, followed by the name of the main chain of atoms with the suffix -in.
the final part of the name is a figure indicating the location of the triple bond in the molecule, for example, butyn-2.

Isomerism of alkynes. Dependence of properties on structure

Ethine and propyne do not have isomers of the triplethey appear, starting with Butin. The isomers of the carbon skeleton are in pentin and the following homologues. The spatial isomerism of acetylenic hydrocarbons is not manifested with respect to the triple bond.

The first 4 ethanol homologues are gases that are poorly soluble in water. Acetylene hydrocarbons C₅ - C₁₅ - liquid. The solids are homologues of ethane, starting from hydrocarbon C₁₇. The chemical nature of alkynes undergoesa significant influence of the triple bond. Hydrocarbons of this type are more active than ethylene, and various particles are attached. This property is based on the widespread use of ethane in industry and engineering. When burning acetylene, a large amount of heat is released, which finds application in gas cutting and welding of metals.