Q. 15 The total number of possible stereoisomers for the compound with the structural formula CH₃CH(OH)CH=CHCH₂CH₃ is ____.
The compound CH₃CH(OH)CH=CHCH₂CH₃, known as pent-3-en-2-ol, has two stereogenic units leading to four possible stereoisomers.
Structural Analysis
Number the carbons: C1 (CH₃-), C2 (-CH(OH)-), C3 (-CH=), C4 (=CH-), C5 (-CH₂CH₃, but formula indicates -CHCH₂CH₃ wait, standard is C1H3-C2H(OH)-C3H=C4H-C5H2C6H3).
C2 attaches to H, OH, CH₃, and C3H=, making it chiral (four different groups).
C3=C4 double bond has C3 attached to H and C2, C4 to H and CH₂CH₃, allowing E/Z (geometric) isomerism.
Types of Stereoisomerism
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Chiral Center: C2 creates two enantiomers (R and S configurations).
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Geometric Isomerism: C3=C4 yields E (trans) and Z (cis) forms.
Combinations produce 2 (geometric) × 2 (optical) = 4 stereoisomers. No meso form exists due to distant stereocenters.
Common Options Explained
| Option | Stereoisomers Count | Reason Incorrect/Correct |
|---|---|---|
| 2 | Only geometric or only optical | Ignores both types present |
| 3 | Asymmetric count | No basis; full tally is even (2^n × geometric) |
| 4 | Both geometric and optical | Matches: (E,R), (E,S), (Z,R), (Z,S) |
| 6 | Extra assumed centers | Only two stereogenic units; no additional chirality |
