| Abstract
| - N-4-R-Benzyl-N-nitrosopivalamides (1a−d; R = MeO, Me, H, NO2) were allowed to decompose at18 °C in C6D12, CDCl3, CD3CN, and d6-DMSO, and the rates of decomposition were followed by 1HNMR spectroscopy. The half-lives of the nitrosoamides were found to vary in a systematic waywith the nature of the R group on the aromatic nucleus. Electron-releasing groups were found todecrease the stability of the starting nitrosoamide, whereas electron-withdrawing ones increasedthe nitrosoamides' thermal stability. A Hammett-type plot of log(rate constants of deamination) vsσp was linear (R2 = 0.986) with a ρ-type value of −0.90 indicating development of significant positivecharge at the benzylic position in the transition state of the rate-determining step. The thermalstability of the nitrosoamides was also found to be systematically affected by the polarity of thesolvent: as the solvent polarity increased, so did the lability of the nitrosoamides. This observationof intra- and intermolecular electronic perturbations of the kinetics of nitrosoamide decompositionappears to be novel. A closer look at the rate-determining step of nitrosoamide thermolysis is made,and a mechanistic framework is proposed that accounts for both steric and electronic modulationof nitrosoamide stability as well as the greater thermal stabilities of the related N-nitrocarboxamidesand N-nitrosotosylamides.
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