Naphthylcarbene and Fluorenylidene

Our work with diphenylcarbene had some technical issues due to overlapping absorptions but was nevertheless straightforward, as the matrix spectrum of the triplet carbene was available and the spectrum of benzhydryl radical was 

Observing Invisible Carbenes By Trapping Them with Pyridine 

LFP of 1-naphthyldiazomethane (10) in acetonitrile, the first solvent we studied, produced a transient spectrum with X = 386 nm. The transient was formed in an exponential process with a time constant of 100 10 ns and decayed over several microseconds. Our initial impulse was to attribute the transient absorbing at 386 nm to triplet 1-naphthylcarbene formed from invisible singlet 1-naphthylcarbene 11 with a time constant of 100 ns. [21] 

Additional work soon discredited this postulate. The 386 nm transient could not be detected in other solvents. No transient was detected upon LFP of 10 in benzene or hexafluorobenzene. In cyclohexane, a transient with X = 367 nm was formed 144 ns after the laser pulse. Only in nitrile solvents were transient absorption bands observed near 400 nm. The definitive experiment was performed by Linda Fladel who demonstrated that the pseudo-first order rate constant of formation of the 386 nm absorbing transient was linearly dependent on the concentration of acetonitrile. This proved that the transient is formed by reaction of an invisible species which reacts with acetonitrile. The observable transient was ylide 12 formed by capture of 11. The same transient was formed by LFP of azirine 13. 

Ylides of singlet 1-naphthylcarbene ( 11) with acetone, triethylamine and pyridine were soon observed. [21] Fluorenylidene was also found to react with coordinating solvents to form ylides. [22] 

---