Upending a fundamental reaction in organic chemistry—discovery of a new nucleophilic substitution reaction
Nucleophilic substitution is a class of chemical reactions encountered throughout organic chemistry, including those used to manufacture common petrochemical and pharmaceutical products. Its underlying mechanism was discovered 82 years ago by the British chemists Edward Hughes and Christopher Ingold, who showed that an electron-rich chemical species, called a nucleophile, "attacks" and replaces an electron-poor fragment of an organic molecule, called a leaving group.
One of the main types of nucleophilic substitution reactions, called SN2, involves the nucleophile attacking and the leaving group departing at the same time. Hughes and Ingold first made the observation, subsequently confirmed by generations of chemists, that SN2 reactions all seemed to occur via "backside attack," whereby the nucleophile joins the organic molecule at a location opposite to the leaving group.
Although SN2 reactions were believed to be understood, a new variant has been found by a group of scientists in Singapore. In an upcoming paper due to be published in the journal Science, a research group led by Professor Choon-Hong Tan of Nanyang Technological University (NTU) reports that SN2 reactions can also occur via "frontside attack," whereby the nucleophile approaches the molecule on the same side as the leaving group.
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