Out of the following compounds, the chiral molecules are
(A) Butan-2-ol
(B) Propan-2-ol
(C) 2-Chlorobutane
(D) 2-Bromopropanoic acid
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (C) and (D) only
A molecule is chiral when it cannot be superimposed on its mirror image. For these simple molecules the test is a carbon atom bonded to four different groups (a stereocentre). If any two of the four groups on that carbon are the same, the molecule has a plane of symmetry and is achiral.
(A) Butan-2-ol — Correct. \( \ce{CH3-CH(OH)-CH2CH3} \): C2 carries H, OH, \( \ce{CH3} \) and \( \ce{C2H5} \), four different groups.
(B) Propan-2-ol — Incorrect. \( \ce{CH3-CH(OH)-CH3} \): C2 carries two identical methyl groups, so the molecule is superimposable on its mirror image.
(C) 2-Chlorobutane — Correct. \( \ce{CH3-CH(Cl)-CH2CH3} \): C2 carries H, Cl, \( \ce{CH3} \) and \( \ce{C2H5} \).
(D) 2-Bromopropanoic acid — Correct. \( \ce{CH3-CH(Br)-COOH} \): C2 carries H, Br, \( \ce{CH3} \) and COOH.
So the chiral molecules are (A), (C) and (D) only.
Shortcut: Propan-2-ol has two methyl groups on the –OH carbon, so (B) is achiral; only Option (4) leaves it out.
NCERT (2026-27 edition):
Molecular Asymmetry, Chirality and Enantiomers – “… The objects which are non- superimposable on their mirror image (like a pair of hands) are said to be chiral and this property is known as chirality. Chiral molecules are optically active, while the objects, which are, superimposable on their mirror images are called achiral.”
Molecular Asymmetry, Chirality and Enantiomers – “… 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-bromopropanoic acid (H3C–CHBr–COOH) …”