Fluorenylidene: kinetics and mechanisms

Exchange effects and cidep

“…The flash photolysis chemistry of fluorenylidene is by now well understood [109,110]. The rate constant for hydrogen abstraction by fluorenylidene from cyclohexane (Figure 21a) is anomalously high for a triplet aromatic carbene at 8.3 x 107 M -i s -1 [109]. We have taken advantage of this high rate constant and shown that the 9-fluorenyl radical produced by photolysis of 9-diazofluorene is generated with absorptive polarization in neat cyclohexane [92].…”

“…The flash photolysis chemistry of fluorenylidene is by now well understood [109,110]. The rate constant for hydrogen abstraction by fluorenylidene from cyclohexane (Figure 21a) is anomalously high for a triplet aromatic carbene at 8.3 x 107 M -i s -1 [109].…”

Photo‐Wolff Rearrangement of 2‐Diazo‐1,2‐naphthoquinone: Stern–Volmer Analysis of the Stepwise Reaction Pathway

“…The ratios of the rate constants of trapping by methanol and of Wolff rearrangement of 2 , k MeOH / k WR , were determined as 3.2 ± 0.2, 1.2 ± 0.2 and 1.7 ± 0.1 m −1 in mixtures of methanol with hexane, dioxane and acetonitrile, respectively. Bimolecular rate constants for OH insertion by singlet carbenes are generally close to the diffusion‐controlled limit , i.e ., around k MeOH ≈ 5 × 10 9 m −1 s −1 . Assuming an upper limit of k MeOH < 1 × 10 10 m −1 s −1 , these values indicate that the rate constant k WR for Wolff rearrangement of the trappable carbene 2 is less than 5 × 10 9 s −1 .…”

Photochemistry of 1‐pyrenyldiazomethane*

“…These intermediates have been generated by laser flash photolysis of a diazo compound or diazirine, which produce the carbene on loss of nitrogen. Once formed, the direct observation of carbene transient absorption has provided valuable information about absolute reactivities of diphenylcarbene (Griller et al, 1984a), fluorenylidene (Griller et al, 1984b), 1-and 2-naphthylcarbene (Barcus et al, 1986;Horn and Chateuneuf, 1985).…”