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:
To answer this question, we are tasked with drawing a six-carbon alkyne that can exist as diastereomers and explaining why diastereomerism is possible in this compound.
✅ Correct Structure:
The correct structure is:
3-Hexyne with two different substituents on carbons 2 and 4 — specifically:
2-bromo-4-chloro-3-hexyne
Structure:
CH₃–CH(Br)–C≡C–CH(Cl)–CH₃
✏️ Explanation (Approx. 300 words):
A diastereomer is a type of stereoisomer that is not a mirror image of another molecule and differs in the spatial arrangement of atoms across two or more chiral centers. In contrast to enantiomers, which are non-superimposable mirror images, diastereomers are non-mirror-image stereoisomers.
To have diastereomers, we need:
- At least two stereocenters, and
- Not all stereocenters are mirrored between the isomers (which would make them enantiomers).
Now, let’s consider the compound:
👉 2-bromo-4-chloro-3-hexyne (CH₃–CH(Br)–C≡C–CH(Cl)–CH₃)
- This is a six-carbon alkyne (satisfying the “six-carbon alkyne” requirement).
- The alkyne is at position 3, forming a linear, sp-hybridized carbon-carbon triple bond between C3 and C4.
- On C2 and C5, each has a carbon attached to a halogen (Br or Cl) and a hydrogen, plus different groups (methyl on one side and the alkyne group on the other), making them chiral centers.
- Because there are two chiral centers (on C2 and C5), this molecule can have multiple stereoisomers.
Let’s look at the stereoisomers:
- RR and SS would be enantiomers (mirror images).
- RS and SR are their own enantiomeric pair.
- RR vs RS, for example, are diastereomers — not mirror images, and not superimposable.
So, this compound has diastereomers due to the presence of two stereocenters that are not symmetrical and a fixed geometry around the alkyne bond, which does not allow free rotation.
Thus, 2-bromo-4-chloro-3-hexyne is a valid six-carbon alkyne that can exist as diastereomers.