Name: Reactions of &#945;-Halocarbonyl Compounds: Nucleophilic Substitution
Uploaded: 2023-04-30T11:29:34
Description: Learn by watching this video about Reactions of α-Halocarbonyl Compounds: Nucleophilic Substitution at JoVE.com

&#945;-halocarbonyl compounds undergo nucleophilic substitution at their &#945;-position via an SN2&#160; pathway.
With &#945;-halo ketones, the nucleophiles used must be less basic since strongly basic nucleophiles result in enolate formation.
On the contrary, &#945;-halo acids react well with strongly basic nucleophiles via the SN2 pathway.
Under basic condition, &#945;-halo acids first ionize to its conjugate-base anion. Further deprotonation of the &#945; hydrogen to form the dianion does not take place and instead, the anionic species undergoes a substitution reaction.
SN1 reactions are unfavorable for &#945;-halocarbonyl compounds, as they form less stable carbocations at the &#945;-position.
The resonance structure of the intermediate carbocation involves electron-deficient oxygen, making it less resonance-stabilized.
Electrostatic interaction of the carbocation with the bond dipole of the carbonyl group also destabilizes the &#945;-carbonyl carbocation.

reactions of &alpha;-halocarbonyl compounds: nucleophilic substitution

Nucleophilic substitution in &#945;-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in &#945;-haloketones is generally carried out with less basic nucleophiles. The use of strong basic nucleophiles leads to the generation of &#945;-&NoBreak;haloenolate ions, which often participate in other side reactions.
<img alt="Figure1" src="/files/ftp_upload/13059/13059_Figure_1.svg" style="text-align: center; height: 105px;" />
However, &#945;-haloacids undergo SN2 reactions with strong basic nucleophiles. Under this condition, the base abstracts the acidic proton of the acid forming its conjugate base. The anion further participates in a substitution reaction, and the final acidification results in &#945;-substituted acids.
<img alt="Figure2" src="/files/ftp_upload/13059/13059_Figure_2.svg" style="text-align: center; height: 80px;" />
In &#945;-halocarbonyl compounds, nucleophilic substitution via an SN1 pathway is forbidden, as it generates less stable &#945;-carbocation intermediate.

Learn by watching this video about Reactions of α-Halocarbonyl Compounds: Nucleophilic Substitution at JoVE.com

Reactions of &#945;-Halocarbonyl Compounds: Nucleophilic Substitution

Reactions of &alpha;-Halocarbonyl Compounds: Nucleophilic Substitution

Nucleophilic substitution in &#945;-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in &#945;-haloketones is generally carried out ...