Identify and indicate the presence of a centre of chirality, if any, in the following molecules. How many stereoisomers are possible for those containing a chiral centre?
i) 1,2-dichloropropane
ii) 3-bromopent-1-ene
i) 1,2-dichloropropane
ii) 3-bromopent-1-ene
Answer: (i) C-2 of CH₃CHClCH₂Cl is chiral → 2 stereoisomers. (ii) C-3 of CH₂=CH–CHBr–C₂H₅ is chiral → 2 stereoisomers.
Solution
(i) 1,2-Dichloropropane: CH–\*CHCl–CHCl. C-2 bears CH, Cl, H and CHCl — four different groups ⇒ chiral centre; stereoisomers (an enantiomeric pair).
(ii) 3-Bromopent-1-ene: CH=CH–\*CHBr–CHCH. C-3 bears vinyl, Br, H and ethyl ⇒ chiral centre; again \textbf{2 stereoisomers} (d/l enantiomers).
(ii) 3-Bromopent-1-ene: CH=CH–\*CHBr–CHCH. C-3 bears vinyl, Br, H and ethyl ⇒ chiral centre; again \textbf{2 stereoisomers} (d/l enantiomers).
CBSE Class 12 Board · 2004 · All India · Subjective