How many of the following molecules are chiral?
2-Chlorobutane, 2-chloropropane, bromochloroiodomethane (BrClCHI), 2-bromopropanoic acid (CH3–CHBr–COOH), 1-chlorobutane, butan-2-ol, propan-2-ol, 2,3-dihydroxypropanal (OHC–CHOH–CH2OH)
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 5
A molecule with a single asymmetric carbon (a carbon bonded to four different groups) is not superimposable on its mirror image, so it is chiral. If any two groups on the carbon are the same, the molecule is achiral.
Chiral:
2-Chlorobutane (C-2: H, Cl, CH3, C2H5)
Bromochloroiodomethane (H, Cl, Br, I)
2-Bromopropanoic acid (C-2: H, Br, CH3, COOH)
Butan-2-ol (C-2: H, OH, CH3, C2H5)
2,3-Dihydroxypropanal (C-2: H, OH, CHO, CH2OH)
Achiral:
2-Chloropropane, CH3CH(Cl)CH3 — C-2 carries two CH3 groups.
1-Chlorobutane, ClCH2CH2CH2CH3 — every carbon carries at least two H atoms.
Propan-2-ol, CH3CH(OH)CH3 — C-2 carries two CH3 groups.
Chiral: 5 molecules.
NCERT (2026-27 edition):
6.7.1 Reactions of Haloalkanes – “…the spatial arrangement of four groups (valencies) around a central carbon is tetrahedral and if all the substituents attached to that carbon are different, the mirror image of the molecule is not superimposed (overlapped) on the molecule; such a carbon is called asymmetric carbon or stereocentre.”
“As you can see very clearly, propan-2-ol (A) does not contain an asymmetric carbon, as all the four groups attached to the tetrahedral carbon are not different. … Thus propan-2-ol is an achiral molecule.”
“Butan-2-ol has four different groups attached to the tetrahedral carbon and as expected is chiral. Some common examples of chiral molecules such as 2-chlorobutane, 2, 3-dihyroxypropanal, (OHC–CHOH–CH2OH), bromochloro-iodomethane (BrClCHI), 2-bromopropanoic acid (H3C–CHBr–COOH), etc.”