How many optically active stereoisomers are possible for butane-2,3-diol?

• A. 1
• B. 2
• C. 3
• D. 4

Butane-2,3-diol has two chiral centers, which means it can form multiple stereoisomers. To determine the number of optically active stereoisomers, we can use the formula 2ⁿ, where n is the number of chiral centers.

Calculating Stereoisomers

In this case, n equals 2 (since there are two chiral centers). Therefore, the calculation is:

• 2² = 4

Identifying Optically Active Isomers

However, not all stereoisomers are optically active. Butane-2,3-diol has one meso form, which is not optically active. Thus, we subtract this from the total count:

• Total stereoisomers: 4
• Meso form: 1
• Optically active stereoisomers: 4 - 1 = 3

Therefore, the number of optically active stereoisomers for butane-2,3-diol is 3. The correct answer is C. 3.