Lyudmila N. Shchegoleva

Reactions of polyfluoroaromatic imidoyl chloride derivatives with S-nucleophilic reagents

Abstract The interactions of N -pentafluorophenylcarbonimidoyl dichloride, N -pentafluorophenylbenzimidoyl chloride and N -pentafluorophenyl (C-pentafluorophenyl) imidoyl chloride with the S-nucleophilic reagents thiourea, sodium N,N -diethyldithiocarbamate, thiocarbonyl difluoride and bis(trifluoromethyl)trithiocarbonate in the presence of CsF or AgSCF 3 , or thiophenol and polyfluorinated thiophenols in the presence of anhydrous K 2 CO 3 , were studied. Reactions with charged S-nucleophiles and with S-nucleophiles in the presence of a base proceeded with preservation of the N-C multiple bond in the reaction products. By varying the reaction conditions in the case of N -pentafluorophenylcar-bonimidoyl dichloride it was possible to substitute one or two chlorines and obtain mono- or di-thioimidates. When C 6 F 5 or SC 6 F 5 groups were present at the C atom of the N-C multiple bond, preferential substitution of the para -fluorine atom occurred. Semiempirical PM3 calculation data were used to explain the direction of these reactions. N -Pentafluorophenylcarbonimidoyl dichloride reacted with sodium N , N -diethyldithiocarbamate or thiourea to give pentafluorophenylisothiocyanate. Depending on the conditions of the reactions of polyfluorinated benzimidoyl chlorides with thiourea, N -pentafluorophenylthioamides and 2-aryl-4,5,6,7-tetrafluorobenzothiazoles were formed. An attempt to produce SCF 3 derivatives from AgSCF 3 was unsuccessful.

Radical cations of branched alkanes in solutions: time-resolved magnetic field effect and quantum chemical studies.

Radical cations of heptane and octane isomers, as well as several longer branched alkanes, were detected in irradiated n-hexane solutions at room temperature by the method of time-resolved magnetic field effect (TR MFE). To identify radical cations, the hyperfine coupling constants as determined by simulation of the TR MFE curves were compared to the constants calculated using the density functional theory (DFT) approach. The g-values of the observed radical cations were close to that of the 2,2,3,3-tetramethylbutane radical cation studied earlier by optically detected electron spin resonance (ESR) and TR MFE techniques. No evidence of the decay of the radical cations of branched alkanes to produce olefin radical cations was found, which was further supported by the observation of positive charge transfer from the observed radical cations to cycloalkane molecules. The lifetimes of the radical cations of the branched alkanes were found to be longer than tens of nanoseconds.

Pseudorotation in Radical Cations of Low-Symmetric Decalin Molecules

Adiabatic potential energy surfaces (PES) of isomeric decalin cations have been found to be the pseudorotational surfaces due to avoided crossing that is typical for the highly symmetric Jahn-Teller active ions rather than for low-symmetric bicyclic systems. According to the UB3LYP/6-31G* data, the height of the barrier to pseudorotation is less than 2 kcal/mol for the trans isomer and about 9 kcal/mol for the cis isomer. Another peculiarity of the cis isomer PES is that the structure of minimum energy lies beyond the pseudorotation gutter. The calculation results are in fair agreement with the experimental electron spin resonance data.

Structure and Stability of Pentafluoroaniline and 4-Aminononafluorobiphenyl Radical Anions: Optically Detected Electron Paramagnetic Resonance, Time-Resolved Fluorescence, Time-Resolved Magnetic Field Effect, and Quantum Chemical Study.

Radical anions (RAs) are the key intermediates of the selective hydrodefluorination of polyfluoroarenes. We used the techniques of optically detected electron paramagnetic resonance (OD EPR), time-resolved fluorescence, time-resolved magnetic field effect (TR MFE), and the density functional theory to study the possibility of RAs formation from 4-aminononafluorobiphenyl (1) and pentafluoroaniline (2) and estimate their lifetimes and decay channels. To our knowledge, both RAs have not been detected earlier. We have registered the OD EPR spectrum for relatively stable in nonpolar solutions 1(-•) but failed to register the spectra for 2(-•). However, we have managed to fix the 2(-•) by the TR MFE method and obtained its hyperfine coupling constants. The lifetime of 2(-•) was found to be only a few nanoseconds. The activation energy of its decay was estimated to be 3.6 ± 0.3 kcal/mol. According to the calculation results, the short lifetime of 2(-•) is due to the RA fast fragmentation with the F(-) elimination from ortho-position to the amine group. The calculated energy barrier, 3.2 kcal/mol, is close to the experimental value. The fragmentation of 2(-•) in a nonpolar solvent is possible due to the stabilization of the incipient F(-) anion by the binding with the amine group proton.

Fluoro-indenes. Part 14. Interaction of perfluorinated 3-methyl-indene and 1-methylene-indan with nitrating agents in anhydrous HF

Abstract The reaction of perfluorinated 3-methyl-indene and 1-methylene-indan with nitrating agents in anhydrous HF leads to the formation of perfluoro-indan containing an oxygen function together with nitrofluorination products. From an analysis of the experimental data and the results of MNDO calculations of the starting compounds (including perfluorinated indene and 2-methyl-indene), their radical cations and polyfluorinated nitro-indanyl cations, a scheme for the process has been suggested including both a classical electrophilic route and a route involving radical cations of the substrates. The latter are assumed to be generated together with NO 2 · from the intermediate nitro-indanyl cations.

Formation of o-H-perfluoroalkylbenzenes from polyfluorobenzocyclobutenes in HFSbF5

Abstract HF adds to perfluorinated benzocyclobutene, 1-methyl- and 1-ethyl-benzocyclobutenes in the presence of SbF 5 to form o -H-perfluoroethyl-, o -H- perfluoroisopropyl-, and o -H-perfluoro-sec-butylbenzenes respectively. Ease of the process decreses in the same order. Perfluoro-1,1- and perfluoro-1,2- diethylbenzocyclobutenes, perfluoroindan and perfluorotetralin remain practically unchanged under these conditions. The different behaviour of benzocycloalkenes may be attributed to the different strain of the alicyclic fragment of the substrate and to the relative stability of carbocations, which may be intermediates or models for the transition state. This is in agreement with the results of quantum-chemical calculations (in the MNDO approximation with full geometry optimization) of the relative energies of substrates and intermediate ions.

Crystal, molecular, and π-electronic structure of 1,3,2-benzodithiazolium chloride

X-Ray diffraction examination and MNDO calculations have shown that 1,3,2-benzodithiazolium chloride (I) is ionic, with a planar heteroaromatic 10π-electron cation. The π-MO of the cation (I) is isolobal with the p-MO of benzo-2,1,3-thiadiazole. In the cation of (I), as in the latter compound, the p-AO of nitrogen and sulfur contribute for the most part to π-MO of differing symmetry (b1 and a2, respectively). This has the consequence that although both nitrogen and sulfur participate in the formation of a single π-system in the thiazolium cation of (I), there is virtually no π-bonding between them. Generally speaking, the π-MO of the (I) cation shows a tendency to localization on separate molecular fragments. The charge on the cation is localized at the SNS group, and the five-membered ring is strongly polarized. These features all reduce the heteroaromaticity of the system.

Interaction of perfluorinated 3-methylindene and 1-methyleneindan with nitrating reagents in anhydrous HF

Abstract The reactions of perfluorinated 3-methylindene and 1-methyleneindan in HNO 3 − HF ( A ), HNO 3 − SbF 5 − HF ( B ) and NO 2 BF 4 − HF ( C ) have been investigated. Along with nitrofluorination products, compounds with oxygen functions were formed which are not the products of transformations of nitroderivatives under the same reaction conditions. Based on analysis of experimental data and the results of quantum-chemical (MNDO) calculations of substrates, their radical cations and polyfluorinated nitroindanyl cations, a scheme of the process has been suggested involving the classical electrophilic route and the route with participation of substrate radical cations. The latter are assumed to be formed together with NO 2 · from the intermediate nitroindanyl cations.