Thermochemical Stability of α-Amino-α-carbonylmethyl Radicals and Their Resonance As Measured by ESR
作者:Frank M. Welle、Hans-Dieter Beckhaus、Christoph Rüchardt
DOI:10.1021/jo961703v
日期:1997.2.1
alpha-amino-alpha-carbonylmethyl radicals 8 have been recorded. No coalescence temperature for the rotation of the two NMe groups was found at temperatures below the decomposition temperature of the radicals. From known coalescence temperatures and rotational barriers of substituted methyl radicals the rotational barrier of >/=17 kcal mol(-)(1) was estimated for the (*)C-N bond in the radicals 8. Enthalpies DeltaH(diss)
已经记录了俘虏性α-氨基-α-羰基甲基自由基8的ESR光谱。在低于自由基的分解温度的温度下,未发现两个NMe基团旋转的聚结温度。根据已知的聚结温度和取代甲基自由基的旋转势垒,估算自由基8中(*)CN键的旋转势垒> / = 17 kcal mol(-)(1)。焓DeltaH(diss)和熵DeltaS(通过ESR的平衡测量已获得7a,c,d均解离成8a,c,d的结果。通过校正7(空间和双生)中的取代基相互作用焓,得到8的自由基稳定焓RSE = -20.7 +/- 1.0 kcal mol(-)(1)。通过添加二烷基氨基和羰基的已知RSE组,RSE = -9。预计9 kcal mol(-)(1)的值为8。10.8kcal mol(-)(1)的实验值和预测值之间的差异归因于协同的俘获性取代作用。发现自由基8与其他单取代和双取代烷基的自由基稳定化焓与它们的ESRaHα偶联常数之间存在线性关系。根据这种相关性,aHα降低1