Question

11. Specific rotation of an optically pure compound [X] is +40. In a reaction the compound [X] is obtained through
a series of chemical reactions. If the specific rotation of solution is -20, what would be the percentage of
laevorotatory isomer in the solution?
(1) 50%
(2) 25%
(3) 75%
(4) 100%​

Answer 1

Answer:

75%.

Explanation:

We will get the laevorotatory isomer from the optical purity which is given by the formulae of specific rotation(given sample) to that of the pure compound *100 which will be 20/40*100 which on solving we will get 50%. So, 100-50 =50% will be the reamining which is the racemic mixture.  

Since, the racemic mixture contains half of both d and l isomer so here we have 25% each of the d and l isomers. Hence, the total l isomers will be 50+25 which will be 75%.