Fragmentation of 2,2,2-triphenylethoxychlorocarbene: evidence for ultrafast fragmentation-rearrangement in excited diazirines.
[reaction: see text] Photolysis of 3-(2,2,2-triphenylethoxy)-3-chlorodiazirine gives 2,2,2-triphenylethoxychlorocarbene which fragments with 1,2-phenyl migration and loss of CO and Cl(-) to yield the 1,1,2-triphenylethyl cation and thence 1,1,2-triphenylethene by proton loss. However, ps and fs laser flash photolysis provides evidence that up to 25% of the alkene product stems from carbocation that arises directly from excited diazirine rather than from the carbene.
Supramolecular Photochirogenesis with Carbenes Entrapped in Cyclodextrins
Two achiral diazirines 1a and 1b have been encapsulated in the inherently chiral cavity of α-cyclodextrin (6-Cy), β-cyclodextrin (7-Cy) and permethylated β-cyclodextrin (TRIMEB) and photolyzed. Because of supramolecular photochirogenesis the generated carbenes afford intramolecular C–H insertion products not as a racemate but one enantiomer is slightly favored. With 1a@(6-Cy)2 the ee of product 7a is doubled. To the best of our knowledge for the first time for carbene reactions, products are imprinted, though modestly, with handedness derived from Cys. The reaction of 1b is highly dependent on the molecular reactor used for inclusion. Whereas 7-Cy is very efficient for favoring dimerization through azine formation, the use of TRIMEB permits exclusive formation of intramolecular insertion product 7b. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Identification of Dihydroxy Aromatic Compounds in a Low-Temperature Pyrolysis Coal Tar by Gas Chromatography−Mass Spectrometry (GC−MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
Dihydroxy aromatics in coal tar undergo rapid coupling reactions with each other and with some coal-derived species during coal pyrolysis and liquefaction. However, only limited information on the structure of dihydroxy aromatics is known. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography−mass spectrometry (GC−MS) were used to characterize the dihydroxy aromatics in a low-temperature pyrolyzed coal tar and its distillate and residue fractions. Negative-ion electrospray ionization (ESI) FT-ICR MS spectra of coal-tar-derived samples had low molecular masses and narrow mass ranges. Negative-ion ESI is extremely selective for the dihydroxy aromatics present in coal tar. The O2 class species had the highest ion intensity among the species in the negative-ion FT-ICR mass spectrum for each sample. Dihydroxy compounds with an aromatic core structure of benzene, indan, biphenyl (and/or acenaphthene), and naphthalene were identified in the distillate fract...