Identify the stereogenic centers, if any, in
(a) 2-Cyclopenten-1-ol and 3-cyclopenten-1-ol
(b) 1, 1, 2-Trimethylcyclobutane and 1, 1, 3-Trimethylcyclobutane
The Correct Answer and Explanation is :
Explanation of Stereogenic Centers:
A stereogenic center (also known as a chiral center) is an atom in a molecule where the interchange of two groups produces a stereoisomer. Typically, a stereogenic center is a carbon atom attached to four different groups. For cyclic compounds, the symmetry of the molecule also plays a key role.
(a) 2-Cyclopenten-1-ol and 3-Cyclopenten-1-ol:
- 2-Cyclopenten-1-ol:
- The structure has a hydroxyl group (-OH) attached to the second carbon of the cyclopentene ring. This carbon is attached to the -OH group, one hydrogen atom, and two distinct sides of the ring (one with the double bond and the other without).
- These four different groups make the second carbon a stereogenic center.
- Stereogenic centers: 1 (at C-2).
- 3-Cyclopenten-1-ol:
- The structure has the -OH group attached to the third carbon of the cyclopentene ring. The third carbon is attached to the -OH group, one hydrogen atom, and two equivalent sides of the ring.
- Since the two sides of the ring are identical, the third carbon is not a stereogenic center.
- Stereogenic centers: 0.
(b) 1,1,2-Trimethylcyclobutane and 1,1,3-Trimethylcyclobutane:
- 1,1,2-Trimethylcyclobutane:
- The molecule has three methyl groups: two on carbon-1 and one on carbon-2. Carbon-2 is attached to the ring, one hydrogen, and two methyl groups. These groups are not distinct, so it is not a stereogenic center.
- Stereogenic centers: 0.
- 1,1,3-Trimethylcyclobutane:
- Carbon-3 is attached to one methyl group, one hydrogen, and two distinct sides of the cyclobutane ring. This makes carbon-3 a stereogenic center.
- Stereogenic centers: 1 (at C-3).
Summary of Stereogenic Centers:
- 2-Cyclopenten-1-ol: 1 stereogenic center (C-2).
- 3-Cyclopenten-1-ol: No stereogenic centers.
- 1,1,2-Trimethylcyclobutane: No stereogenic centers.
- 1,1,3-Trimethylcyclobutane: 1 stereogenic center (C-3).