Radical reactions of a stable N-heterocyclic silylene: EPR study and DFT calculation

Reaction of the stable silylene, 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene, with the free radical sources TEMPO, Hg[P(O)(OPri)2]2, (CO)3CpM-MCp(CO)3 (M = W, Mo), (CO)5Re-Re(CO)5, and toluene leads to radical adducts. The EPR spectra of these radicals indicate that the unpaired electron is delocalized over the silicon-containing five-membered ring.     

EPR spectra of branched fluorinated radicals,derivatives of 2-trifluoromethyl-2-hydroperfluoropentanethione-3

Conclusions EPR was used to study new stable branched fluorinated radicals, adducts of organic and heteroorganic radicals with 2-trifluoromethyl-2-hydroperfluoropentathione-3. Predominant conformations and transition barriers between the radicals have been established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 317–321, February, 1988.     

The ESR study of the influence of fluorinated alcohols on spin-adducts of phosphoryl radicals with C60 and C70: a change of magnetic resonance parameters and exclusive formation of monoadducts

Complex formation of^.C₆₀P(O)(OPrⁱ)₂ or three isomers of^.C₇₀P(O)(OPrⁱ)₂ with fluorinated alcohols CF₃CH₂OH (1), (CF₃)₃COH (2), and (CF₃)₂CHOH (3) results in an increase in the hyperfine splitting constants with the³¹P nucleus by approximately 3–4 G. Only monoadducts are formed when alcohols1–3 are added to toluene saturated solutions of Hg[P(O)(OPrⁱ)₂]₂ and C₆₀ under photochemical conditions of multi-addition of phosphoryl radicals to C₆₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1869–1871, September, 1998.     

EPR study of the transformations of fluoroalkenyl radicals

Conclusions Fluorinated alkenyl radicals containing a double bond at position 4 or 5 relative to the radical site are converted into relatively stable radicals, apparently due to their cyclization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 706–708, March, 1989.We express our gratitude to A. L. Blyumenfel'd for compiling a program for calculation of the EPR spectra.     

Free-Radical Addition of Dialkyl Phosphites to Branched Fluoro-Olefines

Abstract

We found that under UV-radiation, and without radical initiators, some higher fluoro-olefines regioselectively add dialkyl phosphites to give adducts with high yields. The intermediate phosphonyl substituted fluoroalkyl radicals were observed by ESR-technique and their reactivity was studied:     

Spectral study of reactions of La@C82 and Y@C82 with amino-containing solvents

A solvent effect on the electronic absorption UV-VIS and ESR spectra of La@C₈₂ and Y@C₈₂ was found. The UV-VIS spectra of La@C₈₂ in pyridine, dimethylformamide, and hexamethylphosphorotriamide are identical with that of the La@C₈₂ ^– anion, which is evidence for La@C₈₂ reduction in these solvents. In amino-containing solvents, the shape of the ESR spectra depends on the temperature and the time of preparation of the solutions. Changes in the ESR spectra of La@C₈₂ and Y@C₈₂ in dimethylformamide are due to functionalization of these compounds upon reduction.     

Homolytic reactive mass spectrometry of fullerenes: interaction of C60 and C70 with ketones in the electron impact ion source of a mass spectrometer and the comparison of results with those of photochemical reactions of C60 with several ketones in solution

Our previous investigations showed that homolytic reactions of C₆₀ with a number of perfluoroorganic and organomercury(II) compounds occurring under electron impact (EI) in the ionization chamber (IC) of a mass spectrometer could predict the reactivity of C₆₀ towards these compounds in solution or solid state. To expand the scope of this statement, C₆₀ and C₇₀ have been reacted with ketones RCOR₁, where R and R₁ are alkyl, aryl, benzyl, and CF₃, in an IC under EI to yield products of the addition of R^· and R₁^· radicals to the fullerenes, paramagnetic ones being stabilized by hydrogen addition and loss. Experimental evidence in support of a mechanism involving homolytic dissociation of ketone molecules via superexcited states to afford these radicals that react with the fullerenes at the IC surface has been obtained. As anticipated, the reactions between C₆₀ and several ketones conducted in solution under UV irradiation have afforded Me-, Ph-, and CF₃-derivatives of C₆₀. However, some other products have been identified by mass spectrometry and their formation is reasonably explained. When decalin has been employed as a solvent, decalinyl derivatives of the fullerene have been found among the products and the (9-decalinyl)fullerenyl radical has been registered by EPR. Thus, incomplete but reasonable conformity of the results of the reactions of fullerenes with ketones in an IC under EI with those of the reactions of the same reagents in solution under UV irradiation has been demonstrated, and the former results can predict the latter ones to a reasonable extent.     

Application of the Floquet theory to multiple quantum NMR of dipolar-coupled multi-spin systems under magic angle spinning

A new analytical Liouville-space representation of the time-propagator under magic angle spinning (MAS) is introduced using the formalized quantum Floquet theory. This approach has the advantage that it is applicable to the analysis of any type of NMR experiment where MAS is combined with multiple-pulse excitation. General relationships describing the spectral parameters in multiple-quantum (MQ) MAS spectra are derived in this representation. Their use is illustrated with an application to double-quantum (DQ) NMR spectra of dipolar-coupled multi-spin systems. Corresponding to the separation of the MAS time-propagator into a rotor modulated and a dephasing component, two distinct mechanisms for DQ excitation are identified. One of them exploits the rotor-modulated component to excite DQ coherences through dipolar-recoupling techniques, which are familiar for spin pairs. Analytical expressions of the integral intensities and linewidths in the resulting DQ sideband pattern are derived in the form of power series expansions of the inverse rotor frequency, of which coefficients depend on structural parameters. In a multi-spin system they can most reliably be extracted in the fast spinning regime. The other mechanism exploits the dephasing component, which is characteristic to multi-spin systems only. This is shown to give rise to DQ coherences by free evolution at full rotor periods. The possibility to exploit it for selective excitation of higher order MQ coherences is discussed. In either case, the dephasing component also leads to residual broadening. The main results of the theoretical developments are demonstrated experimentally on adamantane.