Cis-Trans Isomers or Configurational Isomers, or Geometric Isomers are the molecules having the same molecular formula. Still, different structural formulas, i.e. the spatial arrangement of atoms within a molecule, is different. If the two functional groups are on the same side of the double bond, it is known as Cis Alkene, but if the two functional groups are on the different sides of the double bond, it is known as Trans Alkene.
Table of Content
- Cis Trans Alkene
- Properties of Cis Trans Alkene
- Alkynes to Trans Alkene
- Difference between Cis and Trans Alkene
- Frequently Asked Questions – FAQs
Cis Trans Alkene
Cis-Trans Isomers are molecules having the same molecular formula. Still, different structural formulas, i.e. the spatial arrangement of atoms within a molecule, is different. If the two functional groups are on the same side of the double bond, it is known as Cis Alkene, but if the two functional groups are on the different sides of the double bond, it is known as Trans Alkene.
Properties of Cis Trans Alkene
Cis Trans Alkene exhibits different physical properties. It is because the spatial arrangement of atoms within a molecule is different. Due to this, it possesses unequal dipole moments contributing to the differences in properties.
Boiling Point of Cis Trans Alkene
Trans Alkene has a lower boiling point than cis alkene. It is because the trans alkene is less polar and more symmetrical. Polarity plays a crucial role in estimating the boiling point of an alkene. Polarity increases the intermolecular force, thereby increasing the boiling point.
- The boiling point of cis pent-2-ene is 37o C, while the boiling point of the trans-pent-2-ene is 36o C. The difference between them is not significant because the bond polarity is weak.
- The boiling point of cis 1,2-dichloroethylene is 60.3o C, while the boiling point of the trans 1,2-dichloroethylene is 47.5o C. The boiling point of trans-1,2-dichloroethylene is less because the C-Cl dipole moment gets cancelled out.
- Butenedioic Acid cis and trans isomers exhibit different properties.
Stability of Cis Trans Alkene
Trans alkene are more stable than cis alkene. Trans alkene has high thermodynamic stability than cis. Further, cis has two functional groups on the double bond’s same side, which is sterically hindered, reducing its stability.
Melting Point of Cis Trans Alkene
Trans Alkene has a higher melting point than cis alkene. It is because the trans alkene is less polar and more symmetrical. Symmetry plays a crucial role in estimating the melting point of an alkene. Symmetry enhances the packing quality in the solid-state, increasing the melting point.
Alkynes to Trans Alkene
Alkynes undergo reductive hydrogenation when reacted with sodium metal dissolved in ammonia to yield corresponding trans alkene. It is also known as metal reduction.
CH3C≡CH3 + Na / NH3 → CH3CH=CHH3 (Trans Alkene)
Difference between Cis and Trans Alkene
| S. No. | Cis Alkene | Trans Alkene |
|---|---|---|
| 1 | If the two functional groups are on the same side of the double bond, it is known as Cis Alkene. | If the two functional groups are on the different sides of the double bond, it is known as Trans Alkene. |
| 2 | Cis alkene are more polar. | Trans alkenes are relatively less polar or non-polar. |
| 3 | Cis alkene has less melting point than trans alkene. | Trans alkene has a high melting point than cis alkene. |
| 4 | Cis alkene has a high boiling point than trans alkene. | Trans alkene has low melting point than cis alkene. |
| 5 | Cis alkene is more soluble in an inert solvent. | Trans alkene is less soluble in an inert solvent. |
Frequently Asked Questions – FAQs
What is a cis-trans isomer?
Cis-Trans Isomers or Configurational Isomers, or Geometric Isomers are the molecules having the same molecular formula. Still, different structural formula, i.e. the spatial arrangement of atoms within a molecule, is different.
Why does cis and trans alkene possess different physical properties?
Cis Trans Alkene exhibits different physical properties. It is because the spatial arrangement of atoms within a molecule is different. Due to this, it possesses unequal dipole moment contributing to the differences in properties.
What is trans alkene?
In an alkene, if the two functional groups are on the different sides of the double bond, it is known as a trans alkene.
What is cis alkene?
In an alkene, if the two functional groups are on the same side of the double bond, it is known as a cis alkene.
How can you synthesise a trans alkene?
We can synthesise a trans alkene by the reductive hydrogenation of alkyne in sodium metal dissolved in ammonia. It is also known as metal reduction.
CH3C≡CH3 + Na / NH3 → CH3CH=CHH3 (Trans Alkene)
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