Anionic rearrangement kinetic evidence

The first intermediates of the Hofmann reaction are A -haloamides e.g. 1), which are subsequently converted to alkaline salts e.g. 2). Both intermediates can be isolated under carefully controlled conditions. Kinetic evidence on both the substituent and isotope effects in the Hofmann rearrangement of various IV-halobenzamides (1) in an aqueous sodium hydroxide solution strongly support a concerted mechanism, involving the bridged anion (3), shown in Scheme 6. 

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