Six extended para-quinones 1–6 with
sterically hindered keto groups have been characterized by UV–VIS,
1H NMR and 13C NMR spectroscopy. Their
electrochemical properties were investigated in pyridine solution using
cyclic voltammetry, differential pulse voltammetry, chronoamperometry
and controlled-potential electrolysis. All species exhibit two
successive one-electron reductions leading to the dianions
via the monoanions; the dianions can be reoxidized to
the quinones. An EE-type mechanism for 1–6 was verified by
computer simulation; the standard rate constants
(ks1 and ks2 ) of the
heterogeneous charge-transfer are in the region of
6.5–12.5 × 10-3 cm
s-1. The first reduction peak potentials show a good
linear relationship with the calculated LUMO energy levels. The radical
anions, prepared electrochemically in the first reduction step, were
persistent for several hours in the absence of air. They were also
characterized by UV–VIS, EPR and ENDOR spectroscopy revealing that
the odd electron is delocalized over the whole π-system.
我们利用紫外-可见光谱、1H NMR 和 13C NMR 光谱对六种具有立体受阻酮基的扩展对位醌 1-6 进行了表征。研究人员在
吡啶溶液中使用循环伏安法、微分脉冲伏安法、计时电流法和控制电位电解法对它们的电
化学特性进行了研究。所有物种都表现出两个连续的单电子还原,通过单阴离子产生二阴离子;二阴离子可被还原成醌。计算机模拟验证了 1-6 的 EE 型机理;异质电荷转移的标准速率常数(ks1 和 ks2)在 6.5-12.5 × 10-3 cm s-1 之间。第一还原峰电位与计算出的 LUMO 能级呈良好的线性关系。在第一还原步骤中通过电
化学方法制备的自由基阴离子在无空气条件下可持续存在数小时。紫外-可见光谱、电致发光光谱和ENDOR光谱也对它们进行了表征,结果表明奇数电子在整个π-系统中是分散的。