Hydrocarbons are the simplest class of organic substances, their molecules have atoms of only two chemical elements - carbon and hydrogen. Most classes of organic compounds are obtained from various hydrocarbons using chemical synthesis methods .
Hydrocarbons are divided into two subclasses - acyclic and cyclic. Acyclic hydrocarbons, or fatty hydrocarbons, or aliphatic hydrocarbons, include the following groups: saturated hydrocarbons (alkanes), unsaturated (alkenes, alkynes, dienes), acyclic terpenes. Cyclic hydrocarbons are represented by groups of cycloparaffins, arenes, and cyclic terpenes. Terpenes are sometimes referred to as objects of study of bioorganic chemistry.
Limit hydrocarbons (alkanes) are carbon and hydrogen compounds, in the molecules of which all the valencies remaining after the carbon atoms are joined together by a simple bond are saturated with hydrogen atoms. All alkanes can be considered as derivatives or homologues of methane. If one hydrogen atom is taken away from methane, which has the molecular formula CH4 , a particle is formed - the radical CH3. Due to the fact that in a molecule of organic matter, carbon is usually tetravalent, the combination of two such radicals causes the appearance of the second representative of the homologous series - ethane (C2H6). If one atom of the hydrogen is taken from ethane, an ethyl radical is formed, which, after combining with CH3, forms a third homolog — propane.
By analyzing the structural formula of propane, it is easy to establish that its composition includes two types of carbon atoms - primary and secondary. Each primary carbon atom binds to one carbon atom with one valency, and the secondary one - with two valencies with two carbon atoms. If you remove the hydrogen atom from the primary carbon atom of propane, the primary propyl is formed, from the secondary - secondary propyl. Attaching methyl to the primary or secondary propyl causes the formation of structural varieties of the fourth homologue. Two compounds are formed - normal butane with a straight carbon chain and isobutane with a branched carbon chain.
Saturated hydrocarbons: structure
A typical representative of alkanes is methane. The molecular formula is CH4. Alkane molecules are characterized by a sigma bond. In a methane molecule, a carbon atom forms four covalent bonds due to one s- and three p-orbitals, and each hydrogen atom due to s-orbitals.
Saturated hydrocarbons: nomenclature and isomerism
In deriving the structural formulas of the homologous series of methane, starting with butane C4H10, we encounter the phenomenon of isomerism. For example, the molecular formula C4H10 corresponds to two individual compounds, C5H12 corresponds to three. Subsequently, the number of isomers with an increase in the number of carbon atoms in the alkane molecule increases. For example, the molecular formula 614 corresponds to five structural formulas and, accordingly, individual substances, 716 - 9, 818 - 18, C10H22 - 76, 1226 - 355. The first four alkanes are gases, the fifth to twelfth are liquids, starting from the sixteenth are liquids .
Chemical properties of saturated hydrocarbons
All saturated hydrocarbons are inert substances. This is due to the fact that in the alkane molecules, carbon and hydrogen atoms are interconnected by sigma bonds; therefore, these compounds cannot attach hydrogen atoms. Alkanes enter into reactions of radical halogenation, nitration, and cleavage. During halogenation, halogen atoms easily replace the hydrogen atoms in the alkane molecule. During nitration, the nitro group easily replaces hydrogen in tertiary, more difficult in secondary and primary carbon atoms.
Limit and unsaturated hydrocarbons are the raw material for a variety of organic substances. By splitting off hydrogen atoms from saturated hydrocarbons, unsaturated ones (alkenes, alkynes) can be obtained .