L. N. Shchegoleva

Pentafluorophenylation of perfluorinated benzocyclobutene, indan, and tetralin by reaction with pentafluorobenzene in SbF5

The reactivity of perfluorinated benzocyclobutene, indan, and tetralin in reaction with pentafluorobenzene in SbF5 medium, and also the relative stability of generated therewith perfluoro-1-phenylbenzocycloalkenyl cations decrease with increasing alicyclic fragment in the benzocycloalkene. Treating the solutions of salts of the above cations with anhydrous HF results in the corresponding perfluoro-1-phenylbenzocycloalkenes, and the hydrolysis of salts furnishes their 1-hydroxy derivatives. In a reaction of 1-hydroxyperfluoro-1-phenylbenzocyclobutene, -indan, and -tetralin with SOCl2 the hydroxy group is replaced by chlorine. Besides with indan and tetralin derivatives form respectively 7-pentafluorophenyloctafluoro-3-chlorobicyclo[4.3.0]hepta-1,4,6-triene and 7-pentafluorophenyldecafluoro-3-chlorobicyclo[4.4.0]octa-1,4,6-triene.

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 σ-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.

Indo study of the angular dependences of isotropic hyperfese interaction constants in the model conformations of the nitrobenzene radical anion

The UHF/INDO calculations of the model conformations of the nitrobenzene radical onion show that rotation of the nitro group relative to the plane of the benzene ring is accompanied by a pyramidal distortion of the group caused by the pseudo-Jahn-Teller effect (vibronic interaction between the ground n and totally symmetric lowest excited σ states). The angular dependences of the14N,13C,1H, and17O Isotropic hyperfine interaction constants are analyzed. Experimental ESR data are interpreted for the radical anions of nitrobenzene derivatives with ortho-alkyl groups.

OUT-OF-PLANE DISTORTIONS OF CHLORINATED NITROBENZENE RADICAL ANIONS

According to UHF/INDO calculations of the model conformations of the chlorinated nitrobenzene radical anions, the rotation of the nitro group relative to the plane of the benzene ring is accompanied by its pyramidal deformation caused by the pseudo-Jahn–Teller effect. The degree of the structural distortions of the chlorinated nitrobenzene radical anions depends on the arrangement of the chlorine atoms in the benzene ring and on the solvent, increasing from DMF to its mixtures with water. The isotropic hyperfine coupling constants and their dependence on the water content in a binary mixture of solvents are interpreted for a number of chlorinated nitrobenzene radical anions.

MNDO Study of the (Anti)aromaticity of Fluorine-Containing Cyclopentadienyl, Indenyl, and Cyclopenta[b]naphthyl Cations

MNDO calculations were performed to estimate the aromaticity (antiaromaticity) of a series of fluorine-containing cyclopentadienyl, indenyl, and cyclopenta[b]naphthyl cations in terms of the Dewar-Breslow criterion which utilizes the difference in the enthalpies of formation of isomeric cations with closed and open π-systems as aromaticity index. The aromaticity is strongly determined by both the structure of the carbon skeleton and the number and position of fluorine atoms. A linear correlation was revealed between the aromaticity index and the energy of the lowest singlet-singlet excitation for cations having a cyclic π-system.

MNDO STUDY OF THE ELECTRONIC STRUCTURE AND POTENTIAL ENERGY SURFACE OF FLUORINATED SINGLET CYCLOPENTADIENYL AND METHYLCYCLOPENTADIENYL CATIONS

The electronic structure and geometry of some symmetric fluorinated singlet cyclopentadienyl and methylcyclopentadienyl cations are studied by the MNDO method. The structure of the potential energy surface (PES), which is a pseudorotation surface, is investigated. Extreme points of the PES, determining the PES barrier, correspond to structures with inverted frontier molecular orbitals. (Anti)aromaticity of fluorinated methylcyclopentadienyl cations is estimated using the Dewar-Breslow criterion.