Hydrocarbons are compounds that contain carbon and hydrogen atoms. These atoms are bonded together in a molecular form by different kinds of chemical bonds. Hydrocarbons have three major types – alkanes, alkenes, and alkynes.
Alkanes vs Alkenes vs Alkynes
The main difference between alkanes, alkenes, and alkynes is that alkanes form a single bond between carbon atoms while alkenes form a double bond while alkynes form a triple bond between the carbon atoms.
Alkanes are also known as paraffin. The valencies of the four-carbon atom are filled by hydrogen atoms. The simplest kind of alkanes is methane, ethane, and even propane. It is widely used for various industrial processes.
While alkenes are called diene. They are unsaturated hydrocarbons because of the presence of a double bond. They can be incorporated into all sizes of rings called cycloalkenes. The simplest kind of alkenes are ethene, propene, and others and can be prepared in the laboratory.
On the other hand, alkynes are called trienes. Alkynes are highly combustible and the simpler alkynes are present in a gaseous state and as the compound becomes bigger, the compound can be found as liquids or even as solids.
Comparison Table Between Alkanes, Alkenes, and Alkynes
| Parameters of Comparison | Alkanes | Alkenes | Alkynes |
| The bond between carbon atoms | Single bond | Double bond | Triple bond |
| Physical properties | Colourless, low molecular weight, high boiling point, and can exist as solids, liquids and gases | Colourless, nonpolar, combustible, strong smell, exist as a gas at room temperature and have more molecular mass | Odourless and colorless (exception – alkynes have a distinctive odor), and have high boiling and melting point with a bigger molecular structure |
| Chemical properties | Do not react with other chemical compounds or free radicals, are weak acids, react with electrophilic reagents, and react with oxygen and hydrogen | Less soluble in water, the longer molecular chain of alkenes have a high boiling point, the polarity of alkanes depend on functional groups | Slightly acidic and electronegative, and is combustible |
| Application | Used in cooking, heating, liquefied petroleum gas (LPG), natural gas, aerosol sprays, in internal combustion engines, and others | Used in the synthesis of plastic, alcohol, fuels, vinyl chloride, ethanol, acrylic acids, glycerol ester, synthetic rubbers and production of crude oil and natural gas, and others | Used in medicines, pharmaceuticals, and other drug preparation applications, polymer, PVC and rubber synthesis. It is commonly used and in industries to ripe fruits and other processes |
| Example | Methane, ethane | Ethene, Propene | Ethyne, propyne |
What is Alkane?
Alkanes are the type of saturated hydrocarbon that has hydrogen and carbon atoms arranged in a tree structure. The carbon-carbon bonds in alkanes are single. The IUPAC (International Union Od Pure and Applied Chemistry) definition of alkanes is that “acyclic branched or unbranched hydrocarbons with a general formula of Cn H (2n+2)”.
The hybridization of alkanes is sp3. It contains four signs of bonds and is joined by carbon atoms. The longest chain of carbon atoms linked together is called the carbon skeleton and is used to determine the size of the alkane.
Alkanes are also known as paraffin since they exhibit wax-like characteristics at certain standard ambient temperature and pressure (SATP). Alkanes can be further classified depending upon the structure – linear branched or cyclic alkanes.
If the alkane has more than three carbon atoms, it can be arranged in various structures and this forms the basis of structural isomers. Alkanes are widely used in petroleum, crude oil, and natural gas. The different examples of methane, ethane, propane, butane, pentane, hexane, heptane, octane, and other various types.
What is Alkene?
Alkenes are a type of unsaturated hydrocarbon that has a carbon-carbon double bond. They are apolar compounds and are very reactive. The double bond of the carbon atoms is bonded by a sigma bond and a pi bond. The bond is very strong and stable than most single covalent bonds.
The double bond is shorter. The bond length of alkenes is 133 pm or 1.33 Å. The hybridization of alkenes is sp2. The alkenes do not freely rotate because of an energetic cost to break. The bond angles of an alkene are about 120° from each other.
Alkenes are stable compounds but undergo several reactions like addition reaction, hydrogenation reaction, hydration, halogenation, hydrohalogenation, oxidation, halohydrin formation, polymerization, metal complexation, alkylation, and numerous other reactions.
Alkynes are widely used in the synthesis of plastic, alcohol, fuels, vinyl chloride, ethanol, acrylic acids, glycerol ester, synthetic rubbers, and production of crude oil and natural gas, and several other industrial processes. The example of alkenes is ethene, propene, butene, pentene, hexene, heptene, octene, nonene, and other isomers.
What is Alkyne?
Alkynes are unsaturated hydrocarbons that contain a carbon triple bond. Alkynes were known as acetylenes initially. The bond angle between the carbon atoms is 180°. The alkynes have a rod-like structure. They are also known as olefins.
The bond length between the C-atoms is very short and 121 pm. The triple bond has a strong bond strength which is about 839 kJ/mol. It has an sp hybridization where the s and p orbitals overlap each other and forms the three bonds.
Alkynes are named by following a suffix of “ene” after that. Alkynes can be synthesized by several processes like cracking or dehydrohalogenation. Alkynes are a reactive functional group and can have the following reactions like hydrogenation, halogen addition, hydration, tautomerism, cycloaddition, oxidation, or trimerization.
Alkynes are widely used in medicines, pharmaceuticals, and other drug preparation applications. Also used for polymer, PVC, and rubber synthesis. It is commonly used in industries to ripe fruits. Examples of alkynes are propyne, butyne, pentyne, hexyne, and others.
Main Differences Between Alkanes, Alkenes, and Alkynes
- The chemical formula of alkanes is Cn H(2n+2), while that of alkenes is Cn H2n while that of alkynes is Cn H(2n-2).
- The hybridization of an alkane is sp3 while that of alkenes is sp2 and that of alkynes is sp.
- Alkanes are saturated hydrocarbon while alkanes and alkynes are unsaturated hydrocarbons.
- Alkanes are called paraffin while alkanes and alkenes are called olefins.
- Alkanes have Van der Waals dispersion force while alkenes have weak dipole-dipole interaction and alkynes have London dispersion forces as the intermolecular force.
- The bond length of alkanes is 153 pm, alkenes are 134 pm while that of alkynes is 121 pm.
Conclusion
Alkanes, alkenes, and alkynes are types of hydrocarbon and have no functional groups. They seem similar compounds but have distinct differences. Under each type, there are further subtypes and are studied in detail under the subject.
Alkanes, alkenes, and alkynes are used in daily processes. They have a major role to play in various industries and manufacturing processes. The characteristics and functions of all the compounds are different and hence their application is different and diverse.
References
- https://pubs.rsc.org/en/content/articlehtml/2009/cc/b820048c
- https://aip.scitation.org/doi/abs/10.1063/1.1680347