Which molecule is a stereoisomer of cis-2-pentene? 0 B C. D
The Correct Answer and Explanation is:
The correct answer is B.
Stereoisomers are molecules that have the same molecular formula and the same connectivity of atoms, but they differ in the spatial arrangement of those atoms. To find the stereoisomer of cis-2-pentene, we need to find a molecule that meets these specific criteria.
First, let’s analyze the starting molecule, cis-2-pentene.
- “Pent” indicates a five-carbon chain.
- “ene” signifies a carbon-carbon double bond.
- “2-“ places this double bond between the second and third carbon atoms.
- “cis” describes the geometry around the double bond, meaning the main carbon chain substituents (a methyl group and an ethyl group) are on the same side of the double bond.
- The molecular formula for any pentene is C5H10.
Now, let’s evaluate the given options:
- Molecule A is 1-pentyne. It has a five-carbon chain but features a triple bond. Its molecular formula is C5H8. Because both its molecular formula and its connectivity (an alkyne instead of an alkene) are different, it is not a stereoisomer of cis-2-pentene.
- Molecule B is trans-2-pentene. It has a five-carbon chain with a double bond between the second and third carbons, just like cis-2-pentene. Therefore, it shares the same molecular formula (C5H10) and the same connectivity. The key difference is its spatial arrangement. The term “trans” indicates that the carbon chain substituents are on opposite sides of the double bond. Since it only differs in its three-dimensional geometry, trans-2-pentene is the stereoisomer (specifically, a geometric isomer or diastereomer) of cis-2-pentene.
- Molecule C is 2-pentyne. It has a triple bond and a molecular formula of C5H8. For the same reasons as molecule A, it cannot be a stereoisomer of cis-2-pentene.
- Molecule D is pentane. This is a saturated alkane, containing only single bonds. Its molecular formula is C5H12. It has a different molecular formula and connectivity, so it is not an isomer of cis-2-pentene.
Therefore, molecule B is the only option that is a stereoisomer of cis-2-pentene.
