Question

Which of the following is not chiral:-

• A. 2-Butanol
• B. 2, 3-Dibromopentane
• C. 3-bromopentane
• D. 2-hydroxypropanoic acid

Answer 1

The Correct Option is C

To determine which of the given compounds is not chiral, we first need to understand what chirality means. A molecule is said to be chiral if it has an asymmetric carbon atom, i.e., a carbon atom attached to four different groups. Such a molecule cannot be superimposed on its mirror image, much like how left and right hands are mirror images but not superimposable.

1. 2-Butanol: The structure of 2-butanol is CH_3-CH(OH)-CH_2-CH_3. The second carbon is attached to four different groups: a hydroxyl group (OH), a methyl group (CH_3), an ethyl group (CH_2CH_3), and a hydrogen (H). This makes 2-butanol a chiral molecule.
2. 2, 3-Dibromopentane: The structure is CH_3-CH(Br)-CH(Br)-CH_2-CH_3. Both the second and third carbon atoms have four different groups attached. Thus, 2, 3-dibromopentane is a chiral molecule.
3. 3-Bromopentane: The structure of 3-bromopentane is CH_3-CH_2-CH(Br)-CH_2-CH_3. The third carbon atom is bonded to a bromine atom, two identical ethyl chains, and a hydrogen. Since it is attached to two identical groups, it does not have four different substituents, making it achiral (not chiral).
4. 2-Hydroxypropanoic acid (lactic acid): The structure is CH_3-CH(OH)-COOH. The second carbon is attached to four different groups: a hydroxyl group (OH), a carboxyl group (COOH), a methyl group (CH_3), and a hydrogen (H). This makes 2-hydroxypropanoic acid a chiral molecule.

Based on the analysis above, 3-bromopentane is the compound that is not chiral because it lacks a carbon atom bonded to four different substituents. The correct answer is 3-bromopentane.