化学
光化学
超快激光光谱学
电泳剂
光激发
激进的
自由基离子
亲电芳香族取代
微秒
药物化学
光谱学
有机化学
激发态
离子
物理
量子力学
核物理学
催化作用
天文
作者
S.M. Hubig,Jay K. Kochi
摘要
The Wheland intermediate in electrophilic aromatic nitrosation, viz. the nitrosoarenium σ-complex, is directly observed by transient absorption spectroscopy. Femtosecond time-resolved laser experiments based on charge-transfer photoexcitation of electron donor/acceptor (EDA) complexes of nitrosonium cation with various arenes reveal the ultrafast formation of nitrosobenzenium to occur in less than 10 ps via the radical/radical coupling of arene cation radicals and nitric oxide. The lifetimes of the σ-complexes in dichloromethane solution are strongly temperature dependentvarying from nanoseconds (T = 298 K) to microseconds (T = 195 K). Steady-state photolysis of arene/NO+ complexes in n-BuCl glasses at T = 77 K leads to nitrosoarenium σ-complexes which persist for several hours. Based on a reaction scheme that includes an ultrafast equilibrium between the [ArH+•,NO•] radical pair and the nitrosoarenium σ-complex, energy diagrams are constructed which establish the highly endergonic reaction profile of electrophilic aromatic nitrosations with the arene/nitrosonium π-complex as the thermodynamic sink.
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