Spectral Properties and Absolute Rate Constants for β-Scission of Ring-Substituted Cumyloxyl Radicals. A Laser Flash Photolysis Study
作者:Enrico Baciocchi、Massimo Bietti、Michela Salamone、Steen Steenken
DOI:10.1021/jo0163041
日期:2002.4.1
to a significant extent the rate constants for beta-scission of the cumyloxyl radicals, which varies between 7.1 x 10(5) and 1.1 x 10(6) s(-1), a result that suggests that cumyloxyl radical beta-scission is not governed by the stability of the resulting acetophenone. Finally, k(beta) increases on going from MeCN to the more polar MeCN/H(2)O 1:1 for all cumyloxyl radicals, an observation that reflects
进行了一系列环取代的枯基氧基自由基的光谱性质和β-断裂反应的激光闪光光解研究。所有的枯基羟自由基在光谱的可见光区域均显示出较宽的吸收带,并在微秒级时域衰减,从而导致光谱的UV区域的吸收度显着增加,这归因于在β-切断枯基氧基。在给电子环取代基的存在下可见吸收带的位置发生红移,而在吸电子环取代基的存在下观察到蓝移,这表明+ R环取代基通过稳定初始自由基两性离子的芳环上的部分正电荷来促进被激发的枯基氧基中的电荷分离。沿着这条线,在枯基氧基的可见光吸收最大值处的实验测量的能量与sigma(+)取代基常数之间获得了极好的Hammett型相关性。对于所有枯基氧基,从MeCN到MeCN / H(2)O也会观察到红移,这表明水具有特定的作用。环取代不会显着影响枯基氧基自由基β断裂的速率常数,该常数在7.1 x 10(5)和1.1 x 10(6)s(-1)之间变化,这一结果表明,枯基氧基自由基β-断裂不受所得苯乙酮稳定性的支配。