Darbeau R W, Pease R S, Gibble R E
Department of Chemistry, McNeese State University, Lake Charles, Louisiana 70609, USA.
J Org Chem. 2001 Jul 27;66(15):5027-32. doi: 10.1021/jo001741l.
N-4-R-Benzyl-N-nitrosopivalamides (1a-d; R = MeO, Me, H, NO(2)) were allowed to decompose at 18 degrees C in C(6)D(12), CDCl(3), CD(3)CN, and d(6)-DMSO, and the rates of decomposition were followed by (1)H NMR spectroscopy. The half-lives of the nitrosoamides were found to vary in a systematic way with the nature of the R group on the aromatic nucleus. Electron-releasing groups were found to decrease the stability of the starting nitrosoamide, whereas electron-withdrawing ones increased the nitrosoamides' thermal stability. A Hammett-type plot of log(rate constants of deamination) vs sigma(p) was linear (R(2) = 0.986) with a rho-type value of -0.90 indicating development of significant positive charge at the benzylic position in the transition state of the rate-determining step. The thermal stability of the nitrosoamides was also found to be systematically affected by the polarity of the solvent: as the solvent polarity increased, so did the lability of the nitrosoamides. This observation of intra- and intermolecular electronic perturbations of the kinetics of nitrosoamide decomposition appears 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 modulation of nitrosoamide stability as well as the greater thermal stabilities of the related N-nitrocarboxamides and N-nitrosotosylamides.
N-4-R-苄基-N-亚硝基新戊酰胺（1a - d；R = 甲氧基、甲基、氢、硝基）在18℃下于氘代十二烷（C₆D₁₂）、氘代氯仿（CDCl₃）、氘代乙腈（CD₃CN）和氘代二甲亚砜（d₆ - DMSO）中分解，分解速率通过¹H核磁共振光谱进行跟踪。发现亚硝基酰胺的半衰期随芳环上R基团的性质呈系统性变化。发现供电子基团会降低起始亚硝基酰胺的稳定性，而吸电子基团则会提高亚硝基酰胺的热稳定性。以log（脱氨基反应速率常数）对σ(p)作图得到的哈米特型曲线呈线性（R² = 0.986），ρ型值为 - 0.90，表明在速率决定步骤的过渡态中苄基位置出现了显著的正电荷。还发现亚硝基酰胺的热稳定性受到溶剂极性的系统性影响：随着溶剂极性增加，亚硝基酰胺的不稳定性也增加。这种关于亚硝基酰胺分解动力学的分子内和分子间电子扰动的观察似乎是新颖的。对亚硝基酰胺热解的速率决定步骤进行了更深入的研究，并提出了一个机理框架，该框架解释了亚硝基酰胺稳定性的空间和电子调节以及相关N - 硝基羧酰胺和N - 亚硝基甲苯磺酰胺更高的热稳定性。
