Which statement best describes an enantiomer?

Which statement best describes an enantiomer?

• A. One of two mirror-image compounds that differ in shape due to the presence of an asymmetric carbon
• B. A molecule that is superimposable on its mirror image
• C. A molecule with identical physical properties in all environments
• D. A pair of diastereomers

Answer: (A)

Enantiomers are non‑superimposable mirror-image molecules that arise when a molecule has a stereogenic center. The statement describes one of two mirror-image compounds that differ in the arrangement around an asymmetric carbon, which is exactly what creates chirality. Because the carbon is chiral, the two configurations cannot be rotated to align, so they are mirror images that cannot be superimposed. In many respects their physical properties are the same in achiral environments, but they rotate plane-polarized light in opposite directions and interact differently with other chiral substances, such as enzymes. The alternative ideas describe either a molecule that would be achiral (superimposable on its mirror image) or pairs that are not mirror images (diastereomers), which do not define enantiomers.

Enantiomers are non‑superimposable mirror-image molecules that arise when a molecule has a stereogenic center. The statement describes one of two mirror-image compounds that differ in the arrangement around an asymmetric carbon, which is exactly what creates chirality. Because the carbon is chiral, the two configurations cannot be rotated to align, so they are mirror images that cannot be superimposed. In many respects their physical properties are the same in achiral environments, but they rotate plane-polarized light in opposite directions and interact differently with other chiral substances, such as enzymes. The alternative ideas describe either a molecule that would be achiral (superimposable on its mirror image) or pairs that are not mirror images (diastereomers), which do not define enantiomers.