Question

Describe advantages and disadvantages of using optical rotation for determining enantiomeric purity and identity of organic compounds

Answer 1

Enantiomers are the non-superimposable mirror images which have similar chemical and physical properties execpting the intreaction of light with them. Enantiomers are classified as R if they rotate the plan polarized light towards right and as S if rotated to left. Opticcal rotation is used as a tool to describe the compound as R or S.

Advantages:

1. One can establish the configuration of the chiral center as R or S.

2. The technique is non-destructive and simple

3. Enantiomeric purity of a racemic mixture can be determined if and ony if we have their pure enantiomers (one should know the optical rotation of pure compouns) .

Disadvantages:

1. If they are no pure enantiomers availble, then one cannot estimate the enanatiomeric purity.

2. If the molecule undergoes mutarotation like glucose molecule, then the optical rotation will change continuously until an equilibrium is acheived.

3. One cannot establish the exact identity of the compound by measure the optical rotation alone as many of them overlap with each other.

For the identification of compounds NMR and IR stands as a prime spectroscopic techniques.