Chemistry of fluorenylidene. Direct observation of, and kinetic measurements on, a singlet and a triplet carbene at room temperature

Abstract

Sir:The chemical and physical properties of carbenes continue to provoke widespread interest. Physical techniques, such as lowtemperature absorptionZ and EPR3 spectroscopy, and CIDNP4 studies have shown the electronic ground state of most carbenes to be the triplet. Product studies, however, have shown that chemical reactions can originate from either the singlet or the triplet state of the ~a r b e n e .~ This reactive duality complicates the mechanistic interpretation of the chemistry of carbenes since, most commonly, the product mixture obtained is the result of an unknown combination of reaction from the singlet and the triplet. In this report, we describe the results of our pulsed-laser spectrophotometric investigation of the chemistry of both singlet ('FI) and triplet (3Fl) fluorenylidene. These carbenes are conveniently

Diazofluorene — A new reagent for fluorescent photochemical labelling of membrane hydrophobic core

“…It may be added here that, as expected, DAF is non-fluorescent, making it easy to follow the course of photolysis. Depending on the conditions of photolysis (i.e., solvent) DAF can give rise to reactions of both singlet and triplet carbenes [10]. Thus, besides 9-cyclohexylfluorene, trace amounts of fluorenone, bifluorenyl and bifluorenylidene are also formed on photolysis of DAF in cyclohexane.…”

Remote inductive effects in the solvolysis of secondary and tertiary 2-norbornyl derivatives. Evidence for nonclassical stabilization of the 2-norbornyl cation

“…The symmetrically bridged structure of the 2-norbornyl cation ( 1) is now established unambiguously.1-9 A wealth of spectroscopic information obtained by direct measurements on the stable ion in superacid media rules out the No dynamic NMR equilibrium corresponding to 2 can be frozen out even at liquid helium temperature.2 Deuterium isotopes should perturb equilibria like 2^2' much more than is observed experimentally. 3 The 13C and *H NMR chemical shifts are inconsistent with 2, but like the other observations, are in full accord with 1.1,3,8 An ab initio method (IGLO) for the accurate calculation of and 13C…”

A Half‐Century Odyssey in the Realm of Reactive Intermediates

“…[28] We did not know it, but Schusters group at the University of Illinois was simultaneously doing similar experiments with singlet and triplet fluorenylidene. [29] Our initial experiments paved the way for the determination of absolute rate constants for the reactions of many singlet carbenes with alkenes (and other substrates) under normal reaction conditions, and led to a delightful collaboration with Nick Turro, including several extended joint group seminars followed by luncheons at a nearby Greek restaurant aptly named The Symposium.…”