Question detail
What causes optical isomers to rotate plane-polarised light in opposite directions?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Optical isomerism (A-level only)
Question
- A. The presence of chiral carbon atoms
- B. The molecular weight of the isomers
- C. The type of functional groups present
- D. The temperature of the solution
Answer
The presence of chiral carbon atoms
Explanation
The presence of chiral carbon atoms in optical isomers creates non-superimposable mirror images. This structural difference leads to the mechanism where each isomer interacts differently with plane-polarised light, causing one to rotate the light clockwise and the other counterclockwise. The effect is that when plane-polarised light passes through a solution of these isomers, it is rotated in opposite directions, which is significant in understanding their optical activity.
Common mistake
Misunderstanding Optical Activity
Students often think that all organic molecules can rotate plane-polarised light, regardless of their structure.
Understand that only chiral molecules, which have a non-superimposable mirror image, can rotate plane-polarised light due to their specific spatial arrangement of atoms.
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