Negative Kinetic Temperature Effect on the Hydride Transfer from NADH Analogue BNAH to the Radical Cation of <i>N</i>-Benzylphenothiazine in Acetonitrile
作者:Xiao-Qing Zhu、Jian-Yu Zhang、Jin-Pei Cheng
DOI:10.1021/jo061145c
日期:2006.9.1
The reaction rates of 1-(p-substituted benzyl)-1,4-dihydronicotinamide (G-BNAH) with N-benzylphenothiazine radical cation (PTZ•+) in acetonitrile were determined. The results show that the reaction rates (kobs) decreased from 2.80 × 107 to 2.16 × 107 M-1 s-1 for G = H as the reaction temperature increased from 298 to 318 K. The activation enthalpies of the reactions were estimated according to Eyring
测定了1-(对位取代的苄基)-1,4-二氢烟酰胺(G-BNAH)与N-苄基吩噻嗪自由基阳离子(PTZ • +)在乙腈中的反应速率。结果表明,随着反应温度从298 K升高到318 K,G = H反应速率(k obs)从2.80×10 7降低到2.16×10 7 M - 1 s - 1。根据Eyring方程估算得出负值(-3.4至-2.9 kcal / mol)。对反应中间体的研究表明,G-BNAH和PTZ之间存在电荷转移络合物(CT络合物)• +是在从G-BNAH到PTZ • +的氢化物转移的前面形成的。当G-BNAH中的取代基G从CH 3 O变为Br时,利用贝内西-希尔德布兰德方程估算CT复合物的形成焓,得到-6.4至-6.0 kcal / mol的值。对可能的反应路径中每个基本步骤的详细热力学分析表明,氢化物从G-BNAH到PTZ • +的转移是通过CT络合物的协同氢化物转移发生的。在不