Recently, a group of researchers from the Nanyang Technological University in Singapore have investigated the novel $\ce {S_N2X}$ mechanism which involves a "frontside attack" on the substrate, rather than the usual "backside attack"$^1$. This may seem peculiar at first. However, the fact that there is favourable halogen bond formation between the electrophilic halogen atom and the incoming nucleophile certainly does help to explain why this unusual "frontside attack" would occur.

There are quite a few other similarly peculiar reactions in organic chemistry in which the nucleophilic species first attacks a halogen atom. These include the Appel reaction and the Corey-Fuchs reaction. I was wondering if the formation of an intially halogen-bonded complex the reason why these reactions can proceed.


  1. Zhang, X.; Ren, J.; Tan, S. M.; Tan, D.; Lee, R.; Tan, C.-H. An enantioconvergent halogenophilic nucleophilic substitution ($\ce {S_N2X}$) reaction. Science 2019, 363, 400-404.

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