Irina V. Beregovaya

Potential energy surface and dissociative cleavage of chlorobenzene radical anion

Abstract Potential energy surface (PES) of the short-lived PhCl − radical anion has been studied by ROHF/6-31+G ∗ and MP2/6-31+G ∗ //ROHF/6-31+G ∗ calculations. The PES peculiarities were found to result from two reasons: (a) the quasi-degeneracy of PhCl − π states; (b) the presence of a low-lying repulsive σ term. The anion meta-stable 2 Π state has been located, and transition state for C–Cl cleavage has been found revealing an asymmetrical non-planar structure. Possible mechanisms of halobenzene anions dissociative cleavage are discussed, with the PhCl − as a model.

Transformations of perfluoroxylenes and perfluoro-p-cymene under the action of Zn(Cu)-D-DMF-H2O.

Abstract Perfluorinated xylenes and perfluoro-para-cymene undergo hydrodefluorination under the action of Zn(Cu)-DMF-H 2 O. Hydrogen enters mainly at the benzyl position of para-dialkybenzenes and at the para position to perfluoroalkyl groups of perfluorinated ortho - and meta -xylenes. The process presumably involves radical anions as intermediates. A product of perfluoro-4-methylbenzyl radical trapping by hexene-1 was obtained. Quantum-chemical calculations of radical anions of the compounds under investigation have been carried out.

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.

Substitution of a Fluorine Atom in Perfluorobenzonitrile by a Lithiated Nitronyl Nitroxide

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (1) lithium derivative was found to react with perfluorobenzonitrile (2) substituting its para-fluorine atom to form 2-(4-cyanotetrafluorophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (3), a new nitronyl nitroxide containing a multifunctional framework of strong electron-withdrawing nature. This result shows the possibility of obtaining multifunctional nitronyl nitroxides via the interaction of paramagnetic lithium derivatives as C-nucleophiles with polyfluoroarenes activated for nucleophilic substitution. The reaction regioselectivity is supported by the data of quantum-chemical calculations, which also show that the reaction follows a concerted pathway without formation of an intermediate. Reduction of nitronyl nitroxide 3 in system NaNO2-AcOH yielded corresponding iminonitroxide 4. Characterization of persistent radicals 3 and 4 obtained by the SNF synthetic strategy includes X-ray crystal structures, electron spin resonance data, and static magnetic-susceptibility measurements. X-ray diffraction analysis of both nitronyl nitroxide and iminonitroxide revealed a complete match of the parameters of their crystal lattices.

Reactions of Perfluorobenzocycloalkenes with Ethyl Cyanoacetate and Methyllithium and Some Transformations of the Products

Reactions of perfluorobenzocycloalkenes (ArFF) with methyllithium and ethyl cyanoacetate involved replacement of fluorine atoms in positions 3 and 4 of perfluorocyclobutabenzene, position 5 of perfluoroindan, and position 6 of perfluorotetralin by CH3 and CH(CN)COOEt groups. Hydrolysis of the resulting esters ArFCH(CN)COOEt gave the corresponding perfluoroarylacetic acids ArFCH2COOH which were converted into dichloroacetyl chlorides ArFCCl2COCl by treatment with PCl5. The reaction of ArFCCl2COCl with SbF5 produced trifluoromethyl derivatives ArFCF3. Decarboxylation of ArFCCl2COOH in DMF afforded dichloromethyl derivatives ArFCCl2H which reacted with CsF on heating to form difluoromethyl analogs ArFCF2H.

Gain in magnetic shielding of the15N nucleus in a successive series of related 10, 12, and 14 π-electron heterocycles: 2,1,3-bensothiadiazole, 1,3,2,4-benzodithiadiazine, and 1,3,5,2,4-benzotrithiadiazine

A significat (≈85 ppm) increase in shielding of the15N nucleus is observed in the successive series of 10, 12, and 14 π-electron heterocycles: 2,1,3-benzothiadiazole, 1,3,2,4-benzodithiadiazine, and 1,3,5,2,4-benzotrithiadiazine, as compared to the gain from both the full and the π-charge of the nitrogen atom. Possible antiaromaticity of the 12 π-electron dithiadiazine, containing a low-lying activation state, does not appear clearly in the15N NMR.

Synthesis and Structure of N-(4-Dialkylaminophenyl)hexafluoro- 1,4-naphthoquinone 4-Imines

The reaction of heptafluoro-1-naphthol with N,N-dialkyl-p-nitrosoanilines or N,N-dialkyl-p-phenylenediamines in the presence of HIO3 gave the corresponding polyfluorinated N-aryl-1,4-naphthoquinone 4-imine derivatives which exist in solution as equilibrium mixtures of Z and E isomers. 2,3,5,6,7,8-Hexafluoro-N-(4-dimethylaminophenyl)-1,4-naphthoquinone 4-imine in crystal has exclusively the Z-isomer structure.

Generation of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations and their relative stability

Treatment of perfluorinated benzocyclobutene, indan, and tetralin with SbF5-SO2Cl2, as well as of their 1,1-dichloro analogs with SbF5, gave 1-chloropolyfluorobenzocycloalken-1-yl cations whose structure was studied by 19F and 13C NMR and confirmed by their transformations into perfluorinated ketones upon hydrolysis. Dissolution of perfluorinated benzocyclobutene, indan, and tetralin in excess SbF5 generated perfluorobenzocycloalken-1-yl cations in equilibrium with their precursors. The relative stability of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations decreases as the size of the alicyclic fragment increases.

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.

Synthesis and E-Z isomerism of 4-(4-dimethylaminophenylimine) derivatives of 3-dialkylamino-2,5,6,7,8-pentafluoro-1,4-naphthoquinones

Amination of 2,3,5,6,7,8-hexafluoro-1,4-naphthoquinone 4-(4-dimethylaminophenylimine) with secondary amines gives the corresponding 3-amino derivatives existing in solutions as a mixture of E and Z isomers about the C=N imine bond.