Palau'chlor: 0% NCS, DMSO: 45% X = Br, 75% h (1.31 g, 77%) NBS: 56% h ; NaBr, oxone: 66% O MeO the Cl atom has departed from the N atom, rehybridization at N from sp to sp 2 occurs and the C-N bond shortens from 1.44 Å (1.42 Å according to X-ray structure) to 1.33 Å., indicating a large energy release during this process. Attempts to determine the ΔΔG if the conjugate anion were to maintain sp 3 character failed as it immediately "fell" into the sp 2 sink. Thus, the driving force is too exothermic for it to remain sp 3 -hybridized. Since the nitrogen of an anomeric amide such as 6 is wellknown to adopt a pyramidal configuration, the process of nitrogen inversion was also calculated and the energy barrier was found to be 3.5 kcal/mol (Figure ), which is similar to that of the ΔG between Palau'chlor and the new reagent (Figure .75 kcal/mol). Given these results, the additional driving force of 6 (compared to Palau'chlor) is attributed to the additional energy released as a result of conjugation between the N-lone pair and the carbonyl group, a structural feature that is absent in Palau'chlor (or any other known halogenation agent for that matter). In addition, kinetic studies using and roflumilast as model substrates were performed, demonstrating that the chlorination reaction has first-order dependences of both substrate and reagent 6 (see SI for details).