Draw a six-carbon alkyne that can exist as diastereomers. You do not need to specify wedge or dashed bonds. Select Draw Rings More Erase / MICH 5 3 2 o
The Correct Answer and Explanation is:
✅ Correct Answer:
A correct structure for a six-carbon alkyne that can exist as diastereomers is:
3-Hexyne with two chiral centers at C2 and C5, e.g.:
CH₃–CH(OH)–C≡C–CH(OH)–CH₃
This compound is called 2,5-dihydroxy-3-hexyne.
🧬 Explanation
To answer this question, we need to understand what makes a molecule a diastereomer and how a six-carbon alkyne can meet that criterion.
1. Understanding Diastereomers
Diastereomers are stereoisomers that are not mirror images of each other and not superimposable. For a molecule to exhibit diastereomerism, it typically needs two or more chiral centers. Changing the configuration at just one chiral center (while keeping others constant) gives a diastereomer.
2. Alkyne Basics
An alkyne contains a triple bond, which is linear (180° bond angles). Importantly, alkynes cannot have cis-trans isomerism around the triple bond because of this linear geometry. So, the stereochemistry must come from chiral centers elsewhere in the molecule.
3. Building the Right Molecule
We are limited to six carbon atoms and must include a triple bond. To allow for diastereomerism, we must also introduce two stereocenters (typically tetrahedral carbon atoms bonded to four different groups).
Consider the molecule:
CH₃–CH(OH)–C≡C–CH(OH)–CH₃
This has:
- 6 carbon atoms
- A triple bond between C3 and C4
- Hydroxyl groups on C2 and C5, both of which are chiral centers
4. Diastereomers from This Structure
Because there are two chiral centers (C2 and C5), there are four stereoisomers possible:
- (2R,5R), (2S,5S) – enantiomers
- (2R,5S), (2S,5R) – diastereomers of the first pair
Thus, this molecule can exist as diastereomers—meeting the problem’s requirements.
✅ Final Note:
This answer demonstrates a valid six-carbon alkyne with stereogenic centers that give rise to diastereomerism, leveraging a solid understanding of stereochemistry principles.
