Alkenes vs Alkynes
Both alkenes and alkynes are hydrocarbons having carbon and hydrogen atoms. There can be other substituents attached to these molecules instead of hydrogens. Therefore, large numbers of molecules are possible. Due to multiple bonds, they have the capability to polymerize and make larger chains. Thus, they are especially valuable in useful polymer synthesis. For example, PVC, rubber, various plastic types, etc.
Alkenes are hydrocarbons with carbon- carbon double bonds. These are also known as olefins. Ethene is the simplest alkene molecule, having two carbons and four hydrogens. It has one carbon- carbon double bond, and the molecular formula is C2H4.
H2C = CH2
When naming the alkenes, “ene” is used instead of “ane” in the end of the name of alkane. The longest carbon chain containing the double bond should be taken and the numbering should be done in a way, to give the minimum number to the double bond. The physical properties of alkenes are similar to the corresponding alkanes. Normally, the alkenes having low molecular weights are in the gaseous form at room temperature. For example, ethane and propene are gases. Alkenes are relatively non-polar molecules; therefore, they dissolve in nonpolar solvents or solvents with very low polarity. Alkenes are slightly soluble in water. Density of alkenes is less than water. Alkenes undergo addition reactions due to its double bonds. For example, in the hydrogenation reaction, two hydrogens are added to the double bond and making the alkene to corresponding alkane. This reaction speeds up in the presence of a metal catalyst. In an addition reaction like this, if the adding reagent is added to the same side of the molecule, it is called a syn addition. If the addition is on opposite sides, it is called an anti addition. Likewise, alkenes undergo various types of additions with molecules like halogens, HCl, water etc. The additions can be of Markonikov or anti- Markonikov type. Alkenes can be synthesized via elimination reactions. When considering the stability of alkenes, the more highly substituted the carbon atoms of the double bond, the greater is the stability. Alkenes may have diasterioisomers, therefore, can show sterioisomerism.
Hydrocarbon molecules with carbon- carbon triple bond are known as alkynes. The common name for this family is acetylenes. Ethylene is the simplest molecule in this family with two carbons and two hydrogens. It has the molecular formula of C2H2 and following is its structure.
H — C ≡ C — H
Alkynes are named in much the same way as alkenes. That is, they are named by replacing the “ane” with “yne” in the end of the name of the corresponding alkane. The chain is numbered to give the carbon atoms of the triple bond the lowest possible number. The physical properties of alkynes are similar to the corresponding alkanes. Normally, the alkynes having low molecular weights are in the gaseous form at room temperature. For example, ethyne is a gas. Alkynes are relatively non-polar molecules; therefore, they dissolve in nonpolar solvents or solvents with very low polarity. Alkynes are slightly soluble in water. Density of alkynes is less than water. Alkynes undergo addition reactions, due to its triple bonds. And they also can be synthesized by elimination reactions. The acetylenic hydrogen of alkyne is acidic in nature.
What is the difference between Alkenes and Alkynes?
• Alkenes have carbon- carbon double bonds, and alkynes have carbon- carbon triple bonds.
• Double bond carbons of alkenes are sp2 hybridized, and in alkynes, the triple bonded carbons are sp hybridized.
• Both alkenes and alkynes are slightly soluble in water. But alkynes are slightly more soluble in water than alkenes.
• Alkynes can be synthesized from alkenes via elimination reactions.
• The acetylenic hydrogen of alkyne is acidic, but in alkenes, the hydrogens bonded to double bonds are not acidic.