Q. The specific rotation of a pure enantiomer is + $16{^\circ}$. Its observed rotation if it is isolated from a reaction with 25% recemisation and 75% retention is
A) $- 12{^\circ}$
B) $+ 12{^\circ}$
C) $+ 16{^\circ}$
D) $- 16{^\circ}$
Explanation
(b)
% Enantiomeric excess
$= \frac{observed\ specific\ rotation}{specific\ rotation\ of\ pure\ enantiomer} \times 100$
Observed specific rotation $= \frac{3/4}{100} \times ( + 16{^\circ}) \times 100$
$= + 12{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.