Question

What will be the effect on the plane of plane polarised light when it passes through a solution of dlbutan-2-ol?

(a) Clockwise rotation

(b) Anti-clockwise rotation

(c) Zero rotation

(d) 180° rotation

I have been asked this question during an online exam.

Question is from Haloalkanes & Haloarenes in section Haloalkanes and Haloarenes of Chemistry – Class 12

Answer 1

Correct answer is (c) Zero rotation

To elaborate: dlbutan-2-ol represents a mixture of dbutan-2-ol (dextro) and lbutan-2-ol (laevo), and is called a racemic mixture. There optical rotation due to one isomer will cancel the rotation due to the other and will have no effect on the polarised light passed through it.