Question

For the molecule \[ \mathrm{CH_3-CH=CH-CH(OH)-CH=CH-CH=C(CH_3)_2} \] the number of all possible stereoisomers is ________.

Hint:

Each chiral center or geometrically restricted C=C bond doubles the possible stereoisomers.

Answer 1

Correct Answer: 8

Step 1: Identify chiral and geometrical centers.
- The carbon bearing –OH group is a chiral center $\Rightarrow 1$ stereocenter.
- There are three C=C bonds:
- The first (C2=C3) → can show cis–trans isomerism.
- The second (C5=C6) → can show cis–trans isomerism.
- The third (C7=C8) is part of isopropenyl ($=C(CH_3)_2$), which cannot show isomerism.
Step 2: Total stereogenic elements.
Thus, we have: \[ n_{\text{stereogenic}} = 1 \text{ (chiral carbon) } + 2 \text{ (C=C bonds)} = 3 \] Step 3: Total number of stereoisomers. \[ N = 2^n = 2^3 = 8 \]
Step 4: Conclusion. The molecule can have 8 stereoisomers.