Limit hydrocarbons: general characteristics, isomerism, chemical properties

Hydrocarbons are the simplest class of organic substances, their molecules have atoms of only two chemical elements - carbon and hydrogen. Of the various hydrocarbons, most classes of organic compounds are obtained by chemical synthesis methods .

Hydrocarbons are divided into two subclasses - acyclic and cyclic. Acyclic hydrocarbons or fatty hydrocarbons or aliphatic hydrocarbons include: saturated hydrocarbons (alkanes), unsaturated (alkenes, alkynes, dienes), acyclic terpenes. Cyclic hydrocarbons are represented by groups of cycloparaffins, arenes and cyclic terpenes. Sometimes terpenes are referred to the objects of studying bioorganic chemistry.

Limit hydrocarbons (alkanes) are compounds of carbon and hydrogen, in molecules of which all the valencies remaining after the bonding of carbon atoms with one another by a simple bond are saturated with hydrogen atoms. All alkanes can be considered as derivatives or homologues of methane. If from methane, which has the molecular formula CH4, to take one hydrogen atom, a radical CH3 is formed. In connection with the fact that in a molecule of organic matter, the carbon, as a rule, is tetravalent, the combination of two such radicals causes the appearance of the second representative of the homologous series - ethane (C2H6). If one ethylene atom is taken from one hydrogen atom, an ethyl radical is formed, which, after joining with CH3, forms the third homologue-propane.

Analyzing the structural formula of propane, it is easy to establish that its molecule includes two types of carbon atoms - primary and secondary. Each primary carbon atom is bound to one carbon atom by its own valence, and the secondary one by two valencies with two carbon atoms. If we take away the hydrogen atom from the primary carbon atom of the propane, a primary propyl is formed, from the secondary - a secondary propyl. The addition to primary or secondary methyl propyl leads to the formation of structural species of the fourth homologue. Form two compounds - normal butane with a straight-chain carboxylic chain and isobutane with a branched carbon chain.

Limit hydrocarbons: structure

A typical representative of alkanes is methane. Molecular formula CH4. Alkane molecules are characterized by a sigma-bond. In the methane molecule, the carbon atom forms four covalent bonds due to one s and three p orbitals, and each hydrogen atom is due to the s-orbitals.

Limit hydrocarbons: nomenclature and isomerism

When deducing the structural formulas of the homologous series of methane, starting with butane C4H10, we encounter the phenomenon of isomerism. For example, the molecular formula of C4H10 corresponds to two individual compounds, C5H12 - three. In the future, the number of isomers increases with the increase in the number of carbon atoms in the alkane molecule. For example, the molecular formula of C6H14 corresponds to the five structural formulas and, accordingly, of the individual substances, C7H16-9, C8H18-18, C10H22-76, C12H26-355. The first four representatives of alkanes are gases, from the fifth to the twelfth, liquids, starting with the sixteenth, solids .

Chemical properties of saturated hydrocarbons

All limiting hydrocarbons are inert substances. This is explained by the fact that in alkane molecules the carbon and hydrogen atoms are linked together by sigma bonds, therefore these compounds can not attach hydrogen atoms. Alkanes enter into radical halogenation, nitration, and cleavage reactions. In the halogenation process, halogen atoms easily replace the hydrogen atoms in the alkane molecule. When nitrating, the nitro group easily replaces hydrogen in tertiary, more difficult - in secondary and primary carbon atoms.

Limit and unsaturated hydrocarbons are raw materials for obtaining a variety of organic substances. By splitting off the hydrogen atoms from the ultimate hydrocarbons, it is possible to obtain unsaturated (alkenes, alkynes).