Question

Which of the following compounds is levorotatory?
(A) D-Glyceraldheyde
(B) L-alanine
(C) Glucose
(D) Fructose

Answer 1

Hint: To solve this question, we need to understand the concepts regarding the optical rotations. We will also go through what is dextrorotatory and what is levorotatory and will have to understand the difference between the two terms.

Complete answer:
Optical rotation is the rotation of the orientation of the plane of polarisation about the optical axis of linearly polarized light as light passes through the substance.
Optical rotation is also known as polarisation rotation or circular birefringence.
So, for the compounds to be called Dextrorotatory the criteria is that , if we pass plane polarized light through them , then they should turn the plane polarized light in the clockwise direction.
Whereas, on the other hand, for the compound to be levorotatory, the optically active compound should rotate the plane polarized light in the anticlockwise direction.
Now let’s discuss the optical activity of the given options on the basis of our above discussion.
D- Glyceraldehyde , L-alanine and Glucose molecules rotate the compound to its right or in clockwise direction when the plane polarized light passes through it.
Whereas, the compound Fructose rotates the plane polarized light to the left or in anticlockwise direction, when light passes through it.
So from the above categorisation of the given compounds we can say that the levorotatory compound is Fructose.
Therefore the correct answer is option D i.e. levorotatory.

Note:
 Fructose is the naturally occurring sugar which is present in the fruits naturally. It is also considered to be the sweetest sugar of all the sugars. Also, it is used in combination with glucose to form the table sugar sucrose.