Geometric Isomers of Methylenes

Persistent Triplet Carbenes

“…The very small D value reported for 9-anthrylcarbene (7a) 61 indicates great ability to delocalize unpaired electrons, thus supporting theoretical predictions. 5.2.3.1.…”

“…61 The ESR spectra of the -isomer ( -62b) also consisted of two sets of triplet peaks of similar intensities, assignable to Z and E rotamers. However, only one set of triplet signals was observed in the ESR spectra of R-62b under the same conditions.…”

“…61 In favorable cases, the ESR spectra of these carbenes exhibit two sets of triplet signals with sufficiently different ZFS parameters to detect and characterize the isomers. 77,78 The magnitude of the ZFS parameters D is largely determined by the spin-spin dipolar interaction of the two electrons at the divalent carbon atom.…”

Detection of keto-, thioxo- and iminocarbenes and the quintet state triplet-triplet ketocarbene radical pairs

“…Only one thioxocarbene and a few closely related iminocarbene triplets have been detected by ESR to date, The existence of geometric isomers in triplet carbenes, initially observed in naphthylmethylenes by Trozzolo et al [41], has been extensively studied and recently reviewed by Roth and coworkers [28]. Here we will only present the essential principles underlying the assignment of the two sets of signals to each individual isomer, on the basis of Roth's pioneering work.…”

An Unconventional Mechanistic Insight into SCF3 Formation from Difluorocarbene: Preparation of 18F‐Labeled α‐SCF3 Carbonyl Compounds

“…[1] As a singlet carbene [2] and the most stable dihalocarbene, [1d] difluorocarbene shows moderate electrophilicity due to both strong inductive effect and electron-donating resonance effect induced by fluorine. The understanding of its reactivity has led to a variety of novel organic transformations, [1] including difluoromethylation, [3] trifluoromethylation, [4] and [2+1] cycloaddition [3a] .…”