Q23 / 150 · MHT CET 2026 (18 April Shift 2) · Chemistry
Which from following compounds is NOT optically active?
- A3 - Bromohexane
- Correct answerB2 - Bromo - 2 - methylbutane
- C2 - Bromopentane
- D2 - Bromo - 3 - methylbutane
Solution
The optical activity of a compound depends on the presence of a chiral carbon atom, which is bonded to four different groups.
In 3-bromohexane, the C3 carbon is bonded to a hydrogen atom, a bromine atom, an ethyl group, and a propyl group. Since all four groups are different, it is chiral and optically active.
In 2-bromo-2-methylbutane, the C2 carbon is bonded to a bromine atom, an ethyl group, and two identical methyl groups. Since two groups are the same, it does not have a chiral center and is optically inactive.
In 2-bromopentane, the C2 carbon is bonded to a hydrogen atom, a bromine atom, a methyl group, and a propyl group. It is chiral and optically active.
In 2-bromo-3-methylbutane, the C2 carbon is bonded to a hydrogen atom, a bromine atom, a methyl group, and an isopropyl group. It is chiral and optically active.
Thus, 2-bromo-2-methylbutane is not optically active.
Answer: 2 - Bromo - 2 - methylbutane
In 3-bromohexane, the C3 carbon is bonded to a hydrogen atom, a bromine atom, an ethyl group, and a propyl group. Since all four groups are different, it is chiral and optically active.
In 2-bromo-2-methylbutane, the C2 carbon is bonded to a bromine atom, an ethyl group, and two identical methyl groups. Since two groups are the same, it does not have a chiral center and is optically inactive.
In 2-bromopentane, the C2 carbon is bonded to a hydrogen atom, a bromine atom, a methyl group, and a propyl group. It is chiral and optically active.
In 2-bromo-3-methylbutane, the C2 carbon is bonded to a hydrogen atom, a bromine atom, a methyl group, and an isopropyl group. It is chiral and optically active.
Thus, 2-bromo-2-methylbutane is not optically active.
Answer: 2 - Bromo - 2 - methylbutane
Hence, the correct answer is option: 'B'.