Question

Which of the following is 'not' true about enantiomers?

• A. They have the same chemical reactivity.
• B. They have the same specific rotation.
• C. They have the same melting or boiling point.
• D. They have the same refractive index.

Hint:

Enantiomers have identical physical properties except for the direction of optical rotation. Diastereomers have different physical properties.

Answer 1

The Correct Option is B

Step 1: Conceptual Understanding:
Enantiomers are a pair of molecules that are non-superimposable mirror images of each other. Despite their structural similarity, they are distinct in how they interact with their surroundings. In an achiral environment (one without chirality), enantiomers exhibit identical physical properties.
Step 2: Detailed Explanation:
Enantiomers share identical physical properties, such as melting points, boiling points, and refractive indices, because they experience the same intermolecular forces (like van der Waals forces and hydrogen bonding). This is why, in an achiral environment, they cannot be distinguished from one another based on these properties. Additionally, their chemical reactivity is the same when interacting with achiral reagents because the chiral centers do not affect these reactions in an achiral context.
However, enantiomers behave differently when it comes to their interaction with plane-polarized light. They are optically active and rotate the plane of polarized light, but in opposite directions. One enantiomer is dextrorotatory (clockwise), while the other is levorotatory (counterclockwise). Although they rotate the light by the same magnitude, the directions of rotation are opposite. This means that enantiomers do not share the same specific rotation. Instead, they have equal and opposite rotations.
Step 3: Final Answer:
Therefore, the statement (B) that enantiomers have the "same" specific rotation is false. They have "equal and opposite" specific rotations.