Alkenes vs. Alkynes

What's the Difference?

Alkenes and alkynes are both types of hydrocarbons, meaning they consist solely of carbon and hydrogen atoms. However, they differ in terms of their chemical structure and properties. Alkenes have a double bond between two carbon atoms, while alkynes have a triple bond between two carbon atoms. This difference in bonding leads to variations in their reactivity and physical properties. Alkenes are more reactive than alkynes due to the presence of a double bond, allowing them to undergo addition reactions with other molecules. On the other hand, alkynes are less reactive but have a higher boiling point and melting point compared to alkenes. Overall, both alkenes and alkynes play important roles in organic chemistry and have various applications in industries such as plastics, pharmaceuticals, and fuels.


Number of Carbon AtomsContains at least one carbon-carbon double bondContains at least one carbon-carbon triple bond
HybridizationSp2 hybridizedSp hybridized
General FormulaCnH2nCnH2n-2
Physical StateCan be gases, liquids, or solidsCan be gases, liquids, or solids
ReactivityLess reactive than alkynesMore reactive than alkenes
Functional GroupCarbon-carbon double bondCarbon-carbon triple bond
IsomerismCan exhibit cis-trans isomerismCan exhibit cis-trans isomerism
ExamplesEthene, propeneEthyne, propyne

Further Detail


Organic chemistry is a fascinating branch of chemistry that deals with the study of carbon compounds. Alkenes and alkynes are two important classes of hydrocarbons that contain carbon-carbon double and triple bonds, respectively. While both alkenes and alkynes share some similarities, they also possess distinct characteristics that set them apart. In this article, we will explore the attributes of alkenes and alkynes, highlighting their structural differences, reactivity, and applications.

Structural Differences

Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. The general formula for alkenes is CnH2n, where n represents the number of carbon atoms. On the other hand, alkynes are also unsaturated hydrocarbons but contain at least one carbon-carbon triple bond. The general formula for alkynes is CnH2n-2. This structural difference leads to variations in their physical properties, such as boiling points and densities.

Physical Properties

Alkenes and alkynes have similar physical properties due to their unsaturated nature. Both classes of compounds are generally less dense than water and have lower boiling points compared to their corresponding alkanes. However, alkynes tend to have slightly higher boiling points and densities than alkenes due to the presence of the triple bond, which increases intermolecular forces. Additionally, the presence of double or triple bonds in alkenes and alkynes results in increased reactivity compared to alkanes.


Alkenes and alkynes exhibit distinct reactivity patterns due to the presence of their respective double and triple bonds. Alkenes are known for their ability to undergo addition reactions, where atoms or groups of atoms are added to the carbon-carbon double bond. This reactivity makes alkenes useful in the synthesis of various organic compounds, such as alcohols, halogenated compounds, and polymers. On the other hand, alkynes are even more reactive than alkenes due to the presence of the carbon-carbon triple bond. They readily undergo addition reactions, as well as other reactions such as hydration, hydrogenation, and halogenation.


Both alkenes and alkynes find numerous applications in various industries. Alkenes, due to their reactivity and ability to form polymers, are widely used in the production of plastics, synthetic fibers, and elastomers. Ethene, the simplest alkene, is a key component in the production of polyethylene, one of the most commonly used plastics worldwide. Alkenes are also used in the synthesis of pharmaceuticals, agrochemicals, and solvents. On the other hand, alkynes have applications in the production of specialty chemicals, such as pharmaceutical intermediates and fine chemicals. They are also used in the synthesis of polymers with unique properties, such as high-temperature-resistant materials.


Both alkenes and alkynes exhibit structural isomerism, where compounds with the same molecular formula have different arrangements of atoms. Alkenes can have cis-trans isomerism when there are two different groups attached to each carbon of the double bond. This isomerism arises due to restricted rotation around the double bond. In contrast, alkynes can have positional isomerism when the triple bond is located at different positions within the carbon chain. These isomeric forms of alkenes and alkynes can have different physical and chemical properties, leading to diverse applications.

Industrial Importance

Alkenes and alkynes play crucial roles in the petrochemical industry. They are obtained from the cracking of petroleum fractions and are used as starting materials for the production of various chemicals. The ability to selectively convert alkenes and alkynes into different functional groups through chemical reactions allows for the synthesis of a wide range of valuable compounds. Additionally, the development of catalysts and reaction conditions has enabled the industrial-scale production of alkenes and alkynes with high efficiency and selectivity.


In conclusion, alkenes and alkynes are important classes of hydrocarbons that possess distinct attributes. While alkenes contain carbon-carbon double bonds and alkynes contain carbon-carbon triple bonds, both classes exhibit increased reactivity compared to alkanes. Alkenes find applications in the production of plastics, fibers, and pharmaceuticals, while alkynes are used in the synthesis of specialty chemicals and high-temperature-resistant materials. Understanding the unique properties and reactivity of alkenes and alkynes is essential for their efficient utilization in various industries and the development of new chemical processes.

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