In this article, we will consider such compounds of organic chemistry as alkanes – the simplest substances of an organic nature. We will study in detail all the main aspects of the structure, various properties and learn about the methods of obtaining these substances and their areas of application.
Alkanes and their structure on the example of methane
Alkanes or saturated hydrocarbons are those hydrocarbons in which carbon atoms are connected to each other by single bonds, and all their other valencies are spent on bonding with hydrogen atoms. Consider the structural features of alkanes, taking a methane molecule. So, methane is the simplest alkane in structure. It has the formula CH4 and is a light, colorless and odorless gas, slightly soluble in water. The electron density in the molecule of this substance is shifted to the only carbon, due to the greater electronegativity of this element.
Let’s go directly to the features of alkanes (for example, methane):
Carbon is in sp3 hybridization – the C atom has four hybridized orbitals. Due to the overlap of s-electron clouds of hydrogen atoms by four hybrid orbitals, sigma bonds of the C-H type appear. The elongated shape of the electron clouds contributes to a more complete overlap with the electron clouds of other atoms. More energy is released and much stronger bonds are formed.
Valence angle = 109 degrees 28 minutes.
The shape of the molecule – the methane molecule is an ordinary tetrahedron, in the center of which is carbon, connected by four simple bonds with hydrogen atoms.
Hydrogens are located at the tops of the figure.
The length of a simple carbon-carbon sigma bond = 0.154 nm.
Homologous series and isomerism of alkanes
Here we list the first ten representatives of the alkane class, which must be learned by heart.
One of them is methane, and all the others are its homologues: methane – CH4 ethane – C2H6 propane – C3H8 butane – C4H10 pentane – C5H12 hexane – C6H14 heptane – C7H16 octane – C8H18 nonane – C9H20 decane – C10H22 Starting with propane, carbon atoms are located zigzag.
For saturated hydrocarbons, only isomerism of the carbon skeleton, that is, structural, is characteristic. In accordance with their structure, alkanes do not have the ability to form spatial, interclass, and other types of isomers.
Nomenclature or naming rules for saturated hydrocarbons
There is a certain algorithm for how to correctly name alkanes of various structures (branched, unbranched):
- Find and mark the longest carbon chain.
- Start numbering from the side to which the branching of the molecule is closer.
- The name will be based on a hydrocarbon with the same number of carbon atoms as in the longest chain.
- Before the base, name all substituents with the obligatory indication of the C atoms to which they are attached.
- When writing the name of the limiting compound, separate the numbers from each other with commas, and the numbers from the words – with hyphens.
This sequence of actions only looks long and difficult to perform, but in the process of solving the necessary exercises, you will acquire the skills to work with the names of alkanes and not only.
Physical properties of limiting compounds
When studying each organic and inorganic substance, one should have an idea of its aggregate state, various abilities and valuable qualities. So: Substances that start with methane and end with butane are colorless and odorless gases.
Compounds from pentane to a hydrocarbon having seventeen carbon atoms are liquids without any color with a characteristic gasoline odor.
Can be easily mixed with each other.
All other limiting compounds have a solid state of aggregation, white color, and a greasy shell.
Chemical properties of alkanes
When studying any organic substances, special attention should be paid to their chemical properties. They are an indicator of the reactivity and reactivity of a compound. Alkanes do not react with concentrated sulfuric and nitric acids. They do not discolor oxidizing solutions such as potassium permanganate or bromine water.
For alkanes, reactions of this type are inherent. Let us examine in more detail the subspecies of substitution reactions.
Alkanes interact mainly with bromine and chlorine. When methane and chlorine interact in the light, we obtain chloromethane (CH3Cl) and hydrogen chloride. Halogenation takes place in four stages with alternate replacement of hydrogen atoms in the methane molecule. In the second, third and fourth stages, light is no longer a prerequisite for the reaction. At the second stage of halogenation, dichloromethane (CH2Cl2) is released, at the third – chloroform (CHCl3), at the fourth – carbon tetrachloride (CCl4).