The <i>D</i> Parameter of Vinyl-Substituted 1,3-Cyclopentanediyl Triplet Diradicals as a Sensitive Tool To Determine Electronic Substituent Effects in Allylic Radicals
作者:Waldemar Adam、Oliver Emmert
DOI:10.1021/jo000216j
日期:2000.6.1
monoradicals A. The observed substituent effects are generally larger and, thus, more accurately measured compared to the previously examined aryl-substituted 1, 3-cyclopentanediyl triplet diradicals P. The vinyl-substituted triplet diradicals reflect accurately the delocalizing propensity of substituents, either through hyperconjugative, mesomeric, or inductive effects. For the methyl group, the small but
在2-甲基四氢呋喃(2-MTHF)玻璃基质中,在77 K下确定了局部乙烯基取代的1、3-环戊二基三基团双自由基V的零场D参数。通过报告的α-超精细偶联常数(r(2)= 0.991,n = 7)和相应的半经验计算(PM3)自旋密度(r(2)= 0.989,n = 16)获得了良好的线性相关性。与先前研究的芳基取代的1,3-环戊二基三基团双基自由基P相比,观察到的取代基效果通常更大,因此可以更精确地测量。乙烯基取代的三基团双基自由基准确反映了取代基的离域倾向,或者通过超共轭,介观或诱导作用。对于甲基 已经清楚地证明了相邻自由基位点的很小但很稳定。在设置卤素的情况下,已确定了溴(0.0010 cm(-)(1))和碘(0.0024 cm(-)(1))取代基的小但确定的重原子效应。有机金属取代基SiMe(3)和SnMe(3)被证明是弱的自旋受体,而硫系列的自旋离域则遵循MeS >> MeSO(2)>