Potential energy surfaces of a stacked dimer of benzene and its radical cation: what remains and what appears.

A stepwise qualitative consideration of the reduction in symmetry for the highly symmetrical "right sandwich" and "twisted sandwich" structures of the stacked benzene dimer caused by the pseudo-Jahn-Teller effect made it possible to construct a scheme of the potential energy surface (PES) of this dimer. Thirty-six equivalent structures of minimum energy are ordered on this extremely flat surface, transforming into each other in an almost barrier-free manner. There are two kinds of these transformations, both of which are pseudorotation.

An Updated View of Primary Ionization Processes in Polar Liquids.

According to picosecond radiolysis data, primary radical cations in irradiated carbonates are very rapidly deprotonated. At the same time, analysis of the radiation-induced fluorescence from carbonate solutions indicates the formation of solvent-related radical cationic species with a relatively long lifetime. We use quantum chemical methods to develop a model of carbonate ionization that reconciles these conflicting data.

Primary Radical Cations in Irradiated Poly(isobutylene).

Using the method of time-resolved magnetic field effect in radiation-induced fluorescence, primary radical cations (RCs) in irradiated poly(isobutylene) (PIB) have been detected for the first time. A comparison of experimental results with the data of quantum chemical calculations suggests that the initial geometry of the ionized fragment of the PIB molecule is close to the geometry of the neutral polymer in the --- conformation. The spin density of the RC in this geometry is delocalized over more than 10 polymer units, and the width of the RC's EPR spectrum is about Δ ≈ 1.

Interaction of spin-correlated radical pair with a third radical: Combined effect of spin-exchange interaction and spin-selective reaction.

The reaction of electron transfer between two paramagnetic particles may be strongly dependent on the total spin state of the pair. Such dependence can be used to control electron transfer in a molecular medium via the control of the spin degrees of freedom. In this work, the spin-selective electron transfer has been studied in a three-spin system composed of a spin-correlated radical ion pair (RIP) and the nitroxide radical, TEMPONE.

Dimer Radical Anions of Polyfluoroarenes. Two More to a Small Family.

While there is a body of experimental data concerning dimers formed by an aromatic molecule and its radical cation, information on the corresponding dimer radical anions (DRAs) is scarce. In this work, evidence for the formation of the DRAs of decafluorobiphenyl and 4-aminononafluorobiphenyl has been obtained by the optically detected electron paramagnetic resonance and the time-resolved magnetic field effect techniques. Theoretical investigation (DFT B3LYP-D3/6-31+G*) of these DRAs and the DRAs of octafluoronaphtalene and 1,2,4,5-tetrafluorobenzene previously detected by Werst has been undertaken to gain greater insight into the structure of the polyfluoroarene DRAs.

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.

Radical Cationic Pathway for the Decay of Ionized Glyme Molecules in Liquid Solution.

Chemical stability of primary radical cations (RCs) generated in irradiated matter determines substantially the radiation resistance of organic materials. Transformations of the RCs of the glyme molecules, R(-O-CH2-CH2-)nO-R (R = CH3, n = 1-4) has been studied on the nanosecond time scale by measuring the magnetic field effects in the recombination fluorescence from irradiated liquid solutions of the glymes. In all cases, the RCs observed were different from that expected for the primary ones and revealed very similar hyperfine couplings independent of the poly(ethylene oxide) chain length and of the substitution of terminal methyl groups by C2H5 or CH2CH2Cl, as has been shown with diglyme as an example.

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.

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.

Intramolecular dynamics of 1,2,3-trifluorobenzene radical anions as studied by OD ESR and quantum-chemical methods.

Ab initio UMP2, RMP2, DFT/UB3LYP, and CBS-QB3 calculations have shown that the adiabatic potential energy surface (PES) of the 1,2,3-trifluorobenzene radical anion is a pseudorotation surface formed by nonplanar stationary structures. The low (approximately 2-4 kcal/mol) energy barriers in the path of pseudorotation imply manifestations of spectral exchange in the ESR spectra of this radical anion. The optically detected ESR of radical ion pairs was used to obtain the ESR spectrum of 1,2,3-trifluorobenzene radical anion in liquid squalane solution and to study temperature variations in the spectrum over the range of 243-325 K.