Key Difference – 1-Butyne vs 2-Butyne
All simple aliphatic hydrocarbons are broadly categorized into three types based on the presence of carbon-carbon single or multiple bonds: alkanes, alkenes, and alkynes. Alkanes are saturated hydrocarbons and contain only single carbon-carbon bonds. The general formula of alkane is CnH2n+2. Some common alkanes include methane, ethane, propane, and butane. Alkenes are the unbranched unsaturated hydrocarbons with at least one carbon-carbon double bond. The general formula of alkene is CnH2n. The simplest alkene is ethylene. Butene, hexene, propene are some common examples for alkenes. Alkynes are the unsaturated hydrocarbons with at least one carbon-carbon triple bond. The general formula of alkyne is CnH2n-2. 1-butyne and 2-butyne are two simple alkynes that contain one carbon-carbon triple bond in different places. Both has the same molecular formula of C4H6, but have some differences. The key difference between 1-butyne and 2-butyne is that in 1-butyene, the triple bond is found between first and second carbon, whereas in 2-butyene, it is found between second and third carbon atoms. Because of this difference, these two substances have entirely different characteristic features.
CONTENTS
1. Overview and Key Difference
2. What is 1-Butyne
3. What is 2-Butyne
4. Side by Side Comparison – 1-Butyne vs 2-Butyne in Tabular Form
5. Summary
What is 1-Butyne?
1-butyne is called a terminal alkyne due to the presence of terminal triple bond between the first and second carbon atoms of the carbon chain. Because of the presence of this terminal bond, 1-butyne can be distinguished from 2-butyene by two main tests. In the first test, ammoniacal cuprous chloride solution gives a red precipitate with 1-butyene, resulting in copper 1-butynide. In the second test, ammoniacal silver nitrate solution reacts with 1-butyne, resulting in silver 1-butynide, which is a white precipitate. Both these two solutions do not react with 2-butyne.
Figure 01: 1-Butyne
1-butyne is an extremely flammable colorless gas. It is dense than normal air. The IUPAC name of 1-butyne is but-1-yne.
What is 2-Butyne?
2-butyne is a non-terminal alkyne, which has its triple bond in the middle of the carbon chain, connecting the second and the third carbon atoms. Unlike terminal alkynes, 2-butyne do not react with either ammoniacal cuprous chloride solution or ammoniacal silver nitrate solution to give characteristic precipitates. The terminal alkyl groups of 2-butyne provide electrons to sp-hybridized carbon, thus stabilizing the alkyene while decreasing the heat of hydrogenation. Hence, the heat of hydrogenation is less in 2-butyne than in 1-butyne. 2-butyne is a colorless liquid and emits a petroleum-like odor. It has a low density than water and is not soluble in water. The IUPAC name is but-2-yne.
Figure 02: 2-Butyne
What is the Difference Between 1-Butyne and 2-Butyne?
1-Butyne vs 2-Butyne |
|
| 1-Butyne is a terminal alkyne with a triple bond that connects first and second carbon atoms. | 2-Butyne is a non-terminal alkyne with a triple bond that connects second and third carbon atoms. |
| Heat of Hydrogenation | |
| Heat of hydrogenation is 292 kJ/mol. | Heat of hydrogenation is 275 kJ/mol. |
| Phase | |
| 1-Butyne is a colorless gas. | 2-Butyne is a colorless liquid. |
| Stability | |
| 1-Butyne is less stable than 2-Butyne due to the presence of terminal triple bond. | 2-Butyne is more stable. |
| With Ammoniacal Cuprous Chloride Solution | |
| 1-Butyne gives a red precipitate of copper 1-butynide. | 2-Butyne gives no such precipitate. |
| With Ammoniacal Silver Nitrate Solution (Tollen’s Reagent) | |
| 1-Butyne gives a white precipitate of silver acetylide. | 2-Butyne gives no such precipitate. |
| IUPAC Name | |
| IUPAC name is but-1-yne. | IUPAC name is but-2-yne. |
| Common Name | |
| Common name is ethylacetylene. | Common name is Dimethylacetylene. |
Summary – 1-Butyne vs 2-Butyne
Both 1-butyne and 2-butyne are hydrocarbons that belong to the group of alkynes. 1-butyne is a terminal alkyne that has a triple bond connecting C1 and C2. It is a colorless gas. 2-butyne is a colorless liquid that has its triple bond connecting C2 and C3 atoms. Hence 2-butyne is a non-terminal alkyne. Due to this difference between 1-Butyne and 2-Butyne, these two hydrocarbons have entirely different chemical and physical properties. However, their chemical formula is the same, i.e., C4H6.
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References:
1. Carey, Francis A., and Richard J. Sundberg. Advanced Organic Chemistry Part A: Structure and Mechanisms. Boston, MA, Springer US, 2007.
2. Lon, Clive. X-Kit FET Grade 12 PHYS SCIENCE CHEMISTRY. South Africa, Pearson, 2008.
3. “1-BUTYNE.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here. Accessed 8 Sept. 2017.
4. “2-BUTYNE.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here. Accessed 8 Sept. 2017.
Image Courtesy:
1. “Ethylacetylene” By Magmar452 – Own work (CC0) via Commons Wikimedia
2. “Dimethylacetylene” By Edgar181 – Own work (Public Domain) via Commons Wikimedia