Structural features of 1,3,5-trifluorobenzene radical anion,as studied by optically detected ESR spectroscopy and quantum chemistry

The ESR spectrum of 1,3,5-trifluorobenzene radical anion was obtained for the first time using optically detected ESR spectroscopy. Experimental data and results of a quantum chemical study of the potential energy surface (density functional theory B3LYP and BHHLYP methods) are indicative of fast interconversions between nonplanar conformations of this radical anion.     

Reactions of α-perfluorophenylpyrylium perchlorates with hydrazine hydrate

Reactions of α-perfluorophenylpyrylium salts with hydrazine hydrate in ethanol afforded derivatives of 1,2-diazepine, dihydro-1H-pyrazole, and/or 1-aminopyridinium salts, depending on the steric characteristics of the substituent in the second α-position. 1-Amino-2-methyl-6-perfluorophenyl-4-phenylpyridinium perchlorate was used to obtain various pyridocyanines.     

Intramolecular Dynamics of the 1,2,4-Trifluorobenzene Radical Anion: An Optically Detected EPR and Quantum Chemistry Study

A previously unknown electron paramagnetic resonance (EPR) spectrum of the 1,2,4-trifluorobenzene radical anion in liquid solution in nonpolar solvent has been obtained by means of the optically detected EPR technique. On the basis of quantum chemical calculations, the observed fluorine hyperfine coupling values and their temperature dependence have been interpreted as a consequence of fast conformational exchange among different nonplanar structures.     

Dipole moments and molecular conformations of acetylpyrimidines

By comparing experimentally determined dipole moments with those derived from vector-addition and semiempirical computation using MNDO and AM 1 approximations the conformations of 4- and 5-acetylpyrimidines were found to be close to planar, while that of 2-acetylpyrimidine exhibited a torsion angle of 90°.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1387–1390, October, 1992.     

Electronic and geometric structure of fluorine-substituted benzyl radicals

According to the data from quantum-chemical calculations and theoretical analysis, the effect of fluorine atoms on the electronic and stereochemical structure of the benzyl radical depends substantially on their position. Fluorine atoms in the ring hinder the out-of-plane distortions of the CH₂ group, and substituted C₆F_nH_{5_n}-CH₂ radicals are accordingly planar radicals. On the other hand, the presence of -fluorine atoms assists pyramidal deformation of the methylene fragment, leading in the case of the ,-difluoro-substituted compounds to the formation of nonplanar pseudo-radical structures. Here the fluorine atoms in the ring at the p and o positions should increase somewhat while those at the m positions should reduce the capacity of the CF₂ group for deformation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1069–1074, May, 1990.     

Unusual Lability of Pentafluorophenoxy Group in Reactions of Potassium Aroxides with Pentafluoropyridine

The kinetics of the reactions of pentafluoropyridine with potassium aroxides, leading to formation of polyfluorinated aryl pyridyl ethers, conform to the Bro/nsted equation. The data obtained for potassium pentafluorophenoxide deviate from the general correlation because of readily occuring reverse reaction, replacement of the pentafluorophenoxy group by released fluoride ion. PM3 calculations of the electronic structure of the reagents, intermediate -complexes, and products showed that the replacement of fluorine in pentafluoropyridine is a charge-controlled process, whereas unusually easy replacement of the pentafluorophenoxy group in the corresponding aryl pyridyl ether by fluorine is explained by structural features of its lowest unoccupied molecular orbital.