Which molecule is a stereoisomer of trans-2-butene?
A.
B.
C.
D.
Answer (2)
The molecule that is a stereoisomer of trans-2-butene is cis-2-butene. Stereoisomers have the same connectivity but different spatial arrangements. Cis-2-butene has the two methyl groups on the same side of the double bond, while trans-2-butene has them on opposite sides. The final answer is B.
Explanation
Understanding the Problem The question asks us to identify a stereoisomer of trans-2-butene from the given options. First, let's understand what trans-2-butene is and what stereoisomers are.
Background Knowledge trans-2-butene is a molecule with the formula C H 3 C H = C H C H 3 . The 'trans' prefix indicates that the two methyl groups ( C H 3 ) are on opposite sides of the double bond. Stereoisomers are molecules with the same molecular formula and the same connectivity of atoms, but with a different arrangement of atoms in space. This can occur due to the presence of a double bond (cis/trans isomerism) or a chiral center (enantiomers).
Analyzing the Options Now, let's analyze the given options:
Option A: This molecule is butane ( C H 3 C H 2 C H 2 C H 3 ). It's an alkane and doesn't have a double bond or a chiral center. It's not a stereoisomer of trans-2-butene because it has a different connectivity.
Option B: This molecule is cis-2-butene. The two methyl groups are on the same side of the double bond. Cis-2-butene and trans-2-butene are stereoisomers because they have the same connectivity but different spatial arrangements due to the double bond.
Option C: This option seems incomplete and doesn't represent a valid molecule.
Option D: This molecule is 1-butene. The double bond is between the first and second carbon atoms. It is a constitutional isomer of 2-butene, not a stereoisomer, because the position of the double bond is different.
Identifying the Stereoisomer Based on the analysis, option B (cis-2-butene) is a stereoisomer of trans-2-butene. They have the same connectivity but different spatial arrangements of the methyl groups around the double bond.
Examples
Stereoisomers are important in drug design because different stereoisomers can have different biological activities. For example, one stereoisomer of a drug might be effective, while another might be toxic or ineffective. Understanding stereoisomerism allows chemists to synthesize drugs with the desired activity and minimize unwanted side effects. In the food industry, stereoisomers can affect taste and smell. For instance, different stereoisomers of menthol have different cooling sensations.
Cis-2-butene is the stereoisomer of trans-2-butene, as they have the same connectivity but differ in spatial arrangement. In cis-2-butene, both methyl groups are on the same side of the double bond, while in trans-2-butene, they are on opposite sides. Therefore, the answer is Option B, cis-2-butene.
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