Question

An optically active isomer rotated the plane polarized light anti clockwise. Then the isomer is:
A.Dextro isomer
B.Laevo isomer
C.Racemic mixture
D.none

Answer 1

Hint: To answer this question we must have the knowledge about optical rotation by a solute of plane polarized light. An optically active isomer will always show a rotation either clockwise or anticlockwise.

Complete step by step solution:
Optical activity is the activity of a compound to rotate the plane polarized light. The light travels linearly and when this linearly polarized light interacts with an optically active compound it rotates the light. The angle with which the light is rotated is known as optical angle or optical rotation. This angle is affected by various factors such as concentration of solute, its molecular structure.
Substances that have ability to create optical activity or have the ability to rotate the plane polarized light are known as optically active substances. Quartz, sugar solution, tartaric acid all are the example of optically active molecules. They are further of two types:
Dextrorotatory: when the substance rotates the incoming plane polarized light towards the right or in clockwise direction then the substance is known as a dextrorotatory.
Laevorotatory: when the substance rotates the incoming plane polarized light towards the left or in anti-clockwise direction then the substance is known as a Laevorotatory.
In the question, it is given to us that it rotated the light in an anti clockwise direction, hence the substance must be laevo isomer.
So, the correct option is B.

Note: The concept of optical rotation is used in chemical kinetics to determine the concentration and time. Racemic mixture is a mixture that contains equal amounts of both the optical active isomer that is dextro and laevo isomers.