ELECTRON SPIN RESONANCE STUDIES OF RADICAL ANIONS AND ION PAIRS IN THE PYRAZINE SERIES

1965 ◽  
Vol 43 (1) ◽  
pp. 224-231 ◽  
Author(s):  
C. A. McDowell ◽  
K. F. G. Paulus
Keyword(s):  
Hyperfine Splitting ◽  
Reasonable Agreement ◽  
Ion Pairs ◽  
Steric Effects ◽  
Molecular Orbital Calculations ◽  
Radical Anions ◽  
Electronic Excitations ◽  
Spin Resonance ◽  
Sodium And Potassium ◽  
Spin Densities

The alkali metal hyperfine interaction in ion pairs of sodium and potassium cations with the radical anions of some methyl-substituted pyrazines and pyridines has been investigated. The electrostatic, electronic, and steric interactions which influence the metal hyperfine splitting are discussed in detail. It is proposed that the variation of the observed hyperfine splitting is due, in some cases, to steric effects, but in the series of m-xylene, 3,5-dimethylpyridine, and 2,6-dimethylpyrazine, the variation is caused by a change in the energy of electronic excitations from the anion to the cation.The results of molecular orbital calculations of the spin densities in tetramethylpyrazine and 3,5-dimethylpyridine are compared with experiment and found to give reasonable agreement.

Radical cations of some substituted pyrenes

1970 ◽  
Vol 48 (13) ◽  
pp. 1996-1999 ◽  
Author(s):  
J. T. Cooper
Keyword(s):  
Electron Spin Resonance ◽  
Sulfur Dioxide ◽  
Chlorine Atom ◽  
Electron Spin ◽  
Hyperfine Splitting ◽  
Boron Trifluoride ◽  
Radical Cations ◽  
Molecular Orbital Calculations ◽  
Spin Resonance ◽  
First Time

The electron spin resonance spectra of several substituted pyrene cations, produced by oxidation with boron trifluoride in sulfur dioxide, are reported. The spectra are analyzed and the splitting constants given. With 4-chloropyrene, hyperfine splitting is observed due to the chlorine atom, for the first time in such a species. Molecular orbital calculations (Hückel and McLachlan) are presented for three of the compounds studied.

Organic and biological spectrochemical studies. XXV. Properties of the p-bis(methylthio)benzene and p-bis(ethylthio)benzene cation radicals

1968 ◽  
Vol 46 (2) ◽  
pp. 317-323 ◽  
Author(s):  
W. F. Forbes ◽  
P. D. Sullivan
Keyword(s):  
Aluminium Chloride ◽  
Molecular Orbital Calculations ◽  
Trans Isomers ◽  
Cation Radicals ◽  
Oxygen Analog ◽  
Cis And Trans Isomers ◽  
Spin Resonance ◽  
Cis And Trans ◽  
Related Compounds ◽  
Spin Densities

The electron spin resonance spectra of the sulfur analogs of the p-dimethoxy and p-diethoxy benzene cation radicals, i.e. the cation radicals of p-bis(methylthio)benzene (1) and p-bis(ethylthio)benzene (2), were investigated in aluminium chloride – nitromethane. The spectra are interpreted in terms of cis–trans isomerism. Empirical molecular orbital calculations support this assignment and yield qualitatively correct spin densities at the ring positions. Comparison of the spectral properties of these species with corresponding compounds containing oxygen atoms indicates changes which can be associated with the greater tendency of the sulfur atom to attract spin density. There is also evidence from the β-alkyl proton splitting constants that the conformation of the radical of 2 differs from that of its oxygen analog. Slightly different g values are again observed for the cis and trans isomers, as previously noted for related compounds.

Association of radical anions with alkali metal cations; II. Quantum-chemical study of the associates of glyoxal, nitrobenzene and fluorenone with lithium

1980 ◽  
Vol 45 (2) ◽  
pp. 351-359 ◽  
Author(s):  
Stanislav Miertuš ◽  
Ondrej Kyseľ ◽  
Pavol Mach
Keyword(s):  
Experimental Data ◽  
Quantum Chemical ◽  
Hyperfine Splitting ◽  
Ion Pairs ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Radical Anions ◽  
Alkali Metal Cations ◽  
Conjugated Molecules ◽  
Energy Ratios

Some radical anions (glyoxal, fluorenone and nitrobenzene) were investigated by the modified LHP method. The calculated effects of cations (in ion pairs) and the effect of the polarity of the medium on energy ratios, conformation, hyperfine splitting constants and electronic spectra in the systems agree well with the available experimental data. It seems that the proposed modified LHP method can be useful in the study of ion-radical systems derived from larger conjugated molecules.

Hochauflösende EPR-Spektroskopie an organischen Radikalen in flüssigen Kristallen mit nematischer Mesophase

1968 ◽  
Vol 23 (10) ◽  
pp. 1626-1638
Author(s):  
K. Möbius ◽  
H. Haustein ◽  
M. Plato
Keyword(s):  
Liquid Crystal ◽  
Electron Spin Resonance ◽  
Long Range ◽  
Electron Spin ◽  
Hyperfine Splitting ◽  
Interaction Theory ◽  
Axially Symmetric ◽  
G Factor ◽  
Spin Resonance ◽  
Spin Densities

In the nematic and isotropic phases of the liquid crystal p-azoxyanisole (PAA) the neutral radicals perinaphthenyl (PNT), triphenylmethyl (TPM), and pentaphenylcyclopentadienyl (PPCPD) have been studied by electron spin resonance techniques. A method is discussed for measuring the degree of ordering of the radicals by means of the observed g factors in the different phases. For PNT and TPM the components of the axially symmetric g tensor are determined and compared with the values predicted by STONE’S g factor theory. The shift of the hyperfine splitting constants (C13 and H1) of PNT and TPM agree rather well with the theoretical shifts calculated by the dipol-dipol interaction theory of Mc CONNELL and STRATHDEE. For TPM, however, the agreement is only satisfactory when all the long range contributions are considered. For PNT and TPM also the signs of the spin densities could be determined. PPCPD shows drastically that the validity of both g factor theory and hfs theory in nematic mesophases breaks down for unplanar molecules with large twist angles.

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