What are Alkanes?
Alkanes are organic compounds composed of carbon and hydrogen atoms with a single covalent bond. Alkanes have the formula CnH2n+2 and are subdivided into three groups: chain alkanes, cycloalkanes, and branched alkanes.
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Alkane as saturated hydrocarbons
Alkanes are a class of compounds containing single covalent bonds between carbon and hydrogen atoms. These substances are called saturated hydrocarbons. This class of compounds is composed of carbon and hydrogen atoms connected by a single covalent bond. Contains also a homologous series with the molecular formula CnH2n+2.
Alkanes are the simplest hydrocarbon family. They are only composed of carbon and hydrogen. Every carbon atom forms four bonds, while every hydrogen atom forms one. Chemists prefer line-angle formulas over condensed structural formulas because they are simpler and quicker to draw. Alkane structural formulas can be written in yet another abbreviated form.
Methane, a simple alkane, has one carbon atom and the molecular formula CH4. As this compound contains only a single covalent bond, its structural formula is
Additional carbon atoms are attached to one another in a long-chain alkane molecule via a single covalent bond. Each atom is covalently bonded to four hydrogen atoms, for a total of four single covalent bonds. This structure is referred to as octane. An eight-carbon alkane has a molecular formula – C8H18 and structural formula-
List of Alkanes and their structures
Below is a list of Alkanes with their molecular formulas and structures.
| List of Alkanes | Molecular Formula | Structure |
| Methane | (CH4) | |
| Ethane | (C2H6) | |
| Propane | (C3H8) | |
| Butane | (C4H10) | |
| Pentane | (C5H12) | |
| Hexane | (C6H14) | |
| Heptane | (C7H16) | |
| Octane | (C8H18) | |
| Nonane | (C9H20) | |
| Decane | (C10H22) |
Physical Properties of Alkanes
1. The Solubility of Alkanes
- Due to the small difference in electronegativity between carbon and hydrogen and the covalent nature of the C-C or C-H bonds, alkanes are typically nonpolar molecules.
- Polar molecules are typically soluble in polar solvents, whereas non-polar molecules are soluble in non-polar solvents. Therefore, alkanes are hydrophobic, meaning they are insoluble in water.
- Nevertheless, they are soluble in organic solvents because the energy required to overcome the existing Van Der Waals forces and generate new Van Der Waals forces is comparable.
2. The Boiling Point of Alkanes
- As the intermolecular Van Der Waals forces increase as the molecular size or surface area of the molecule increases, we observe the following:
- The boiling point of alkanes increases as their molecular weight increases.
- It is observed that the straight-chain alkanes have a higher boiling point than their structural isomers.
3. The Melting Point of Alkanes
- The melting point of alkanes follows the same pattern as their boiling point, that is, it rises as the molecular weight of the molecule increases.
- This is due to the fact that higher alkanes are solids and intermolecular forces of attraction are difficult to overcome.
- Even-numbered alkanes are observed to have a higher melting point trend than odd-numbered alkanes because they pack well in the solid phase, forming a structure that is difficult to break.
Alkanes Formula and its Condensed Structures
Alkane structural formulas can be written in abbreviated form. Pentane’s structural formula contains three CH2 methylene groups in the middle of the chain, for instance. We can then compose the structural formula by grouping them together. The first five alkanes with unbranched chains are listed in the table below.
| Name | The molecular formula of alkane | Condensed structural formula of alkane |
| methane | CH4 | CH4 |
| ethane | C2H6 | CH3CH3 |
| propane | C3H8 | CH3CH2CH3 |
| butane | C4H10 | CH3(CH2)2CH3 |
| pentane | C5H12 | CH3(CH2)3CH3 |
Each vertex and line terminus represents a carbon atom, whereas each line represents a bond.
Alkane Formula Chemistry
Formulas of organic compounds contain information of varying degrees of complexity. Molecular formulas, such as that of octane, provide the number of each type of atom present in the molecule of a compound. C8H18 is the molecular formula for multiple alkanes, each of which has a distinct chemical, physical, and toxicological properties. These various compounds are designated by structural formulas that depict the arrangement of atoms within a molecule. Compounds with identical molecular formulas but distinct structural formulas are referred to as structural isomers.
From alkanes, the majority of organic compounds can be derived. In addition, numerous important parts of organic molecules contain one or more alkane groups, minus a hydrogen atom, that are covalently bonded to the basic organic molecule as substituents. Due to these factors, the names of numerous organic compounds are derived from alkanes.
Branched Chain Alkane Formula
Similar to other organic compounds, carbon atoms in alkanes can form straight chains, branched chains, and rings. Straight-chain alkanes, branched-chain alkanes, and cycloalkanes are the three types of alkanes. CnH2n+2 is the general formula for straight-chain and branched-chain alkanes, while CnH2n is the formula for cyclic alkanes.
In the diagram, each of the four hydrocarbon molecules contains eight carbon atoms. In one molecule, all the carbon atoms are in a straight chain, in two they are in branched chains, and in the fourth, six carbon atoms form a ring.
Alkyl Groups
A carbon-hydrogen bond of an alkane molecule is converted into a carbon-substituent bond when a substituent such as a halogen forms a bond with it. As an illustration, when methane reacts with chlorine, a new compound known as chloromethane is formed. A CH3 group is covalently bonded to a chlorine atom to form the new compound.
When hydrogen is removed from a single bond of an alkane, it is referred to as an alkyl group. This Alkyl group is frequently represented by the letter R, similar to how the letter X represents halogens. Here is a generalized reaction between methane and chlorine.
Frequently Asked Questions – FAQs
Q.1 What are the names of the first four alkanes?
The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10). Methane gas, with the molecular formula CH4, is the most elementary alkane.
Q.2 How can alkanes be categorized?
Alkanes are hydrocarbon atoms with a single bond. There are three types of alkanes: straight linear alkanes, branched alkanes, and cyclic alkanes.
Q.3 Does alkane belong to a functional group?
Alkanes are typically not considered functional groups; rather, they are compounds devoid of functional groups. The double carbon-carbon bond is a functional group in alkenes.
Q.4 What is the formula for alkyne in general?
Alkynes are compounds that have the general molecular formula CnH2n2.
Q.5 What is the most elementary alkyne?
Alkynes are triple-bond carbon-carbon hydrocarbons. They lack both geometric and optical isomerism. As shown on the right, ethyne (HCCH), also known as acetylene, is the easiest alkyne.
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