Draw a six-carbon alkyne that can exist as diastereomers

Draw a six-carbon alkyne that can exist as diastereomers. You do not need to specify wedge or dashed bonds.

The correct answer and explanation is :

To illustrate a six-carbon alkyne that can exist as diastereomers, consider the compound 2,3-hexadiyne. This molecule consists of a six-carbon chain with two triple bonds located at the second and third carbon atoms (C≡C-C≡C), making it an alkyne.

Structure of 2,3-hexadiyne:

CH≡C-CH2-CH2-C≡C-CH3

Explanation of Diastereomers:

Diastereomers are stereoisomers that are not mirror images of each other and differ in the arrangement of atoms or groups around one or more chiral centers or double/triple bonds.

For 2,3-hexadiyne, there are two key factors that allow the molecule to exist as diastereomers:

1. Cis/Trans Isomerism at the Alkyne Bonds:

• Alkyne bonds (C≡C) have the possibility to adopt cis or trans configurations. These refer to the spatial arrangement of substituents relative to the triple bond.
• In 2,3-hexadiyne, one or both of the alkyne bonds can have cis (where the substituents are on the same side of the triple bond) or trans (where the substituents are on opposite sides of the triple bond) orientations. This leads to different spatial arrangements of the molecule.

1. Position of the Substituents:

• On a six-carbon chain, the triple bonds at positions 2 and 3 can be arranged in different ways, which influences the relative spatial arrangement of the remaining substituents (e.g., hydrogen atoms or alkyl groups) on the carbon chain.

Diastereomeric Pairs:

• Cis-2,3-hexadiyne and Trans-2,3-hexadiyne are examples of diastereomers. The difference lies in the spatial arrangement of the alkyl groups around the alkyne bonds.

These compounds are diastereomers because they have different configurations at the alkyne bonds, which results in different physical properties (e.g., melting point, boiling point) but are not mirror images of each other.

In summary, 2,3-hexadiyne can exist as diastereomers because the cis and trans isomerism of the alkyne groups leads to different spatial arrangements that are not mirror images, making them non-enantiomeric but diastereomeric.