Question

How many optical isomers are possible for lactic acid:

• A. 4
• B. 0
• C. 6
• D. 2

Hint:

Optical isomers exist when a molecule has at least one chiral center. Use \( 2^n \) to determine the number of isomers, where \( n \) is the number of chiral centers.

Answer 1

The Correct Option is D

Step 1: Understanding optical isomerism. Optical isomerism arises when a compound has a chiral center (an atom, usually carbon, attached to four different groups). Lactic acid (\( \text{CH}_3\text{CH}(\text{OH})\text{COOH} \)) contains one chiral carbon atom, making it capable of existing as two enantiomers (non-superimposable mirror images). 

Step 2: Calculation of optical isomers. The number of optical isomers for a compound is given by \( 2^n \), where \( n \) is the number of chiral centers. For lactic acid, \( n = 1 \): \[ \text{Number of optical isomers} = 2^1 = 2 \] 

Step 3: Why other options are incorrect. - (A) 4: This would require two chiral centers. 
- (B) 0: Incorrect, as lactic acid has a chiral center. 
- (C) 6: This is not possible with one chiral center.