The molecules cis-2-pentene and trans-2-pentene are an example of a pair of:
isotopes
stereoisomers
constitutional isomers
identical molecules
The Correct Answer and Explanation is :
The correct answer is stereoisomers.
Cis-2-pentene and trans-2-pentene are both forms of the same basic molecular formula C5H10, but they differ in the spatial arrangement of the atoms around the double bond, specifically at carbon 2. This difference in spatial arrangement is crucial in defining them as stereoisomers.
Stereoisomers are molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. Within stereoisomers, there are two main types: enantiomers and diastereomers. Enantiomers are mirror images of each other and non-superimposable, while diastereomers are not mirror images. Cis-2-pentene and trans-2-pentene fall into the category of diastereomers because they are not mirror images of each other.
In cis-2-pentene, the two CH3 (methyl) groups are on the same side of the double bond. This configuration leads to a higher energy state due to steric strain because the similar groups are closer together, which often results in different physical properties such as boiling points, melting points, and densities compared to its trans counterpart.
In contrast, in trans-2-pentene, the CH3 groups are on opposite sides of the double bond, which typically makes the molecule more stable and gives it different physical properties than its cis counterpart. This stability arises because the methyl groups are farther apart, reducing the steric hindrance and the overall energy of the molecule.
These differences in physical and chemical properties stemming from molecular geometry are why cis and trans forms of an alkene like 2-pentene are such classic examples of diastereomers in organic chemistry. Understanding these properties is critical in fields ranging from material science to biochemistry, as the subtle differences can lead to significantly different behaviors in a chemical environment.