Electronic substituent effects on the EPR-spectral D parameter of trimethylenemethane (TMM) triplet diradicals compared with localized cyclopentane-1,3-diyls
作者:Manabu Abe、Waldemar Adam
DOI:10.1039/a708236c
日期:——
The EPR-spectral D parameter for a series of aryl-substituted trimethylenemethane (TMM) derivatives 2a–g has been determined in a 2-methyltetrahydrofuran (MTHF) matrix at 77 K. Although the substituent effects on the D parameter are relatively small compared with those of the localized 1,3-diradicals 4, the good correlation between the D values of TMMs 2 and those established for 4 signifies that electronic
在2-甲基四氢呋喃(MTHF )基质中,在77 K下测定了一系列芳基取代的三亚甲基甲烷(TMM)衍生物2a–g的EPR光谱D参数。尽管与D参数相比,取代基对D参数的影响相对较小对于局部1,3-双自由基4而言,TMM 2的D值与为4确定的D值之间的良好相关性表明,也可以以这种方式对交叉共轭三重态物质进行足够的电子取代基效应监测。因此,p -NO 2基团起自旋受体的作用,而p-F取代基表现为自旋给体。在芳基取代的TMM 2a–m中,显着的空间效应会产生扭曲的构象,从而降低了苄基自由基中心的共轭,并导致这些TMM三联体对D参数的取代作用较小。此外,在扭曲构象的苄基位置处AM1 / AUHF计算的自旋密度与TMM三线态双基2的实验D值之间观察到良好的线性。