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:
Answer:
A six-carbon alkyne that can exist as diastereomers would be a 1,3-disubstituted hex-3-yne with chiral centers on carbons adjacent to the triple bond.
One example is:
CH3–CH(OH)–C≡C–CH(OH)–CH3**
Here, the alkyne is between carbons 3 and 4 (hex-3-yne), and the hydroxyl groups on carbons 2 and 5 create chiral centers.
Explanation:
- Structure of Alkynes and Chirality: Alkynes are hydrocarbons with at least one carbon-carbon triple bond (C≡C). A simple alkyne without substituents usually has no stereochemistry because the triple bond is linear and carbons involved in the triple bond are sp-hybridized and achiral.
- Creating Chirality near Alkynes: To have stereoisomerism in alkynes, you need to introduce substituents that create chiral centers. Because the triple bond itself is linear and symmetrical, stereochemistry usually arises from substituents on adjacent carbons.
- Diastereomers: Diastereomers are stereoisomers that are not mirror images of each other. They occur when there are multiple stereocenters. In the given molecule, carbons 2 and 5 are chiral centers due to the presence of hydroxyl groups (–OH) attached to them and different substituents around them.
- Why This Molecule Can Have Diastereomers: The molecule CH3–CH(OH)–C≡C–CH(OH)–CH3 has two stereocenters at C2 and C5. Each stereocenter can be R or S, so:
- Both centers R (RR)
- Both centers S (SS)
- One R, one S (RS)
- One S, one R (SR)
- Why No Need to Specify Wedges/Dashes: Since the question only asks to draw the alkyne that can exist as diastereomers, the general structural formula suffices. The chiral centers exist and are implied by the substituents on carbons adjacent to the triple bond.
Summary:
A six-carbon alkyne can exist as diastereomers if it contains at least two stereocenters. A hex-3-yne substituted with hydroxyl groups on carbons 2 and 5 fulfills this, creating two chiral centers that give rise to multiple stereoisomers, including diastereomers. This structure demonstrates how alkynes can be involved in stereochemistry beyond their linear triple bonds.
