Endo entry to the nortricyclyl-norbornenyl cation system: stereochemistry in the fragmentation of endo-5-norbornenyl-2-oxychlorocarbene

Fragmentation of (S)-endo-5-norbornenyl-2-oxychlorocarbene [(S)-8] in cyclohexane-d12 gives approximately 20% (S)-endo-2-chloro-5-norbornene [(S)-7] with approximately 50% ee, 65-70% (R)-exo-2-chloro-5-norbornene [(R)-4] with >95% ee, and approximately 12% (R)-3-nortricyclyl chloride [(R)-5] with approximately 22% ee. (Analogous stereochemical results were also obtained starting with the enantiomeric carbene (R)-8.) The (S)-8 to (S)-7 and (S)-8 to (R)-4 conversions are ascribed mainly to retention and inversion S(N)i transition states, respectively. These have been located by computational methods and are nearly isoenergetic. In more polar solvents (CDCl3 and CD3CN), the fragmentation of (S)-8 increasingly occurs via competitive ion pair pathways in which steroselectivity is diminished, and escape to the norbornenyl-nortricyclyl cation directs the products away from endo-2-chloro-5-norbornene toward exo-chloride 4 and nortricyclyl chloride 5.     

Negative ion formation in compounds relevant to SF6 decomposition in electrical discharges

Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF₂ SOF₄, SO₂F₂, SF₄, SO₂, and SiF₄ compounds which can be formed by electrical discharges in SF₆. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F^– and SOF ₂ ^–* from SOF₂; SOF ₃ ^– and F^– from SOF₄; SO₂F ₂ ^–* , SO₂F^–, F ₂ ^– , and F^– from SO₂F₂; SF ₄ ^–* and F^– from SF₄; O^–, SO^–, and S^– from SO₂; and SiF ₃ ^– and F^– from SiF₄. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF ₂ ^–* , SO₂F ₂ ^–* , and SF ₄ ^–* are also reported.     

Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

2-Thienylchlorocarbene: reactivity toward alkenes

Absolute rate constants for the additions of syn- and anti-2-thienylchlorocarbenes to various alkenes have been measured. The reactivity, selectivity, and structures of these species were characterized experimentally and computationally.     

Unprecedented chemistry of an aryloxychlorodiazirine: generation of a dihalodiazirine and diazirinone

The reaction of p-nitrophenoxychlorodiazirine with tetrabutylammonium fluoride follows three channels: (1) approximately 17% of p-nitrophenoxide/fluoride exchange to chlorofluorodiazirine and p-nitrophenol, (2) approximately 28% of Cl/F exchange to p-nitrophenoxyfluorodiazirine, and (3) approximately 55% of ipso fluoride attack, affording p-nitrofluorobenzene and the previously unknown diazirinone (diazacyclopropenone).     

Tracking "invisible" alkylchlorocarbenes by their sigma --> p absorptions: dynamics and solvent interactions

Contrary to implications in the literature, the sigma --> p absorptions of alkylchlorocarbenes (RCCl) are readily acquired by laser flash photolysis with UV-vis detection in solution at ambient temperature. Examples include RCCl with R = methyl, benzyl, t-butyl, 1-adamantyl, and cyclopropyl. These absorptions permit direct monitoring of carbene reactions and the formation of carbene-solvent complexes. The kinetics of the reactions of "free" and complexed MeCCl and PhCH2CCl were directly followed with tetramethylethylene and 1-hexene. Particularly effective complexation was provided by anisole and 1,3-dimethoxybenzene, which modulated the rates of intermolecular carbene additions. Computational studies are presented, which aid in understanding the carbene absorption spectra and the nature of the solvent complexes.