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 the Question:
We need to count how many optical isomers lactic acid can form.

Step 2: Key Concept:
Optical isomers arise from chiral centers, carbon atoms attached to four different groups. The total count of optical isomers follows the formula \[ N = 2^n \] where \( n \) is the number of chiral centers in the molecule.

Step 3: Detailed Explanation:
Lactic acid has the structure \( \text{CH}_3\text{CH}(\text{OH})\text{COOH} \).
Looking at the central carbon, it is bonded to a methyl group, a hydroxyl group, a hydrogen atom, and a carboxyl group, four different substituents.
This makes it exactly one chiral center, so \( n = 1 \).
Substituting into the formula: \[ N = 2^1 = 2 \]
This gives two non-superimposable mirror-image forms, the D and L (or R and S) enantiomers of lactic acid.

Step 4: Final Answer:
Lactic acid has 2 possible optical isomers.