Stereoisomers from chiral centers and geometric isomerism

Steps:

• Identify the structure: CH3-CH=CH-CH(OH)-CH(OH)-CH3, with a C=C double bond between carbons 2-3 and OH groups on carbons 4-5.
• Locate chiral centers: Carbons 4 and 5 each have four different substituents (H, OH, CH=CH-CH3, CH3), yielding 2 chiral centers.
• Calculate optical isomers: 2^n = 2^2 = 4 configurations for the chiral centers.
• Add geometric isomers: The C=C double bond allows E/Z isomerism, doubling the total to 4 × 2 = 8 stereoisomers.

Why D is correct:

• The formula for total stereoisomers multiplies optical (2^chiral centers) and geometric (2 for E/Z) possibilities, giving 8 distinct forms.

Why the others are wrong:

• A: Counts only E/Z, ignoring chiral centers.
• B: Counts only chiral centers, ignoring the double bond.
• C: Assumes one meso form reduces chiral isomers to 3, but no meso exists due to the double bond asymmetry.

Final answer: D