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Date: 26-11-2019
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Date: 21-10-2020
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Date: 29-10-2020
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Alkynes can be a useful functional group to synthesize due to some of their antibacterial, antiparasitic, and antifungal properties. One simple method for alkyne synthesis is by double elimination from a dihaloalkane.
One case in which elimination can occur is when a haloalkane is put in contact with a nucleophile. The table below is used to determine which situations will result in elimination and the formation of a π bond.
Type of Haloalkane | Weak Base, Poor Nucleophile | Weak Base, Good Nucleophile | Strong, Unhindered Base | Strong, Hindered Base |
Primary | ||||
Unhindered | E2 | |||
Branched | E2 | E2 | ||
Secondary | E1 | E2 | E2 | |
Tertiary | E1 | E1 | E2 | E2 |
* Empty Box means no elimination or 9pi) bond forms
To synthesize alkynes from dihaloalkanes we use dehydrohalogenation. The majority of these reactions take place using alkoxide bases (other strong bases can also be used) with high temperatures. This combination results in the majority of the product being from the E2 mechanism.
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أول صور ثلاثية الأبعاد للغدة الزعترية البشرية
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