Substituent effects on benzyl radical ESR hyperfine coupling constants. The .sigma..alpha..cntdot. scale based upon spin delocalization

1983 ◽  
Vol 105 (5) ◽  
pp. 1221-1227 ◽  
Author(s):  
Julian M. Dust ◽  
Donald R. Arnold
Keyword(s):  
Hyperfine Coupling ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Hyperfine Coupling Constants ◽  
Benzyl Radical ◽  
Spin Delocalization

Substituent effects on benzylic radical hydrogen hyperfine coupling constants. Part 4. The effect of branching of the alkyl substituent

1985 ◽  
Vol 63 (9) ◽  
pp. 2378-2383 ◽  
Author(s):  
Danial D. M. Wayner ◽  
Donald R. Arnold
Keyword(s):  
Hyperfine Coupling ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Esr Spectra ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Methyl Ethyl ◽  
Hyperfine Coupling Constants ◽  
Benzyl Radical ◽  
Spin Resonance

The effects of substituents in the meta and para positions of the benzyl radical on the α-hydrogen hyperfine coupling constants (hfc's) are discussed. The electron spin resonance (esr) spectra of the para-methyl, ethyl, isopropyl, and tert-butyl substituted benzyl and cumyl radicals are analysed. Hyperconjugation involving the C—C bond is 40–60% as effective as C—H hyperconjugation for delocalizing spin density. This conclusion is supported by INDO molecular orbital calculations. Similar analysis of the 13Cmr spectra of the para-alkyl substituted cumyl carbocations provides evidence that C—C hyperconjugation is 75–90% as effective as C—H hyperconjugation for delocalizing charge density.

A comparison of electron spin resonance α- and β-hyperfine coupling constants in para-substituted α-phenethyl radicals

1986 ◽  
Vol 64 (4) ◽  
pp. 769-772 ◽  
Author(s):  
Donald R. Arnold ◽  
A. Martin de P. Nicholas ◽  
Kent M. Young
Keyword(s):  
Electron Spin Resonance ◽  
Experimental Evidence ◽  
Linear Relationship ◽  
Electron Spin ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Hyperfine Coupling Constants ◽  
Spin Resonance ◽  
Benzyl Radicals ◽  
Spin Delocalization

The linear relationship between the electron spin resonance hyperfine coupling constants (hfc) of the α- and β-hydrogens of para-substituted α-phenethyl radicals provides experimental evidence that the magnitude of both the α- and β -hfc is determined largely by the extent of spin delocalization in these benzylic systems. The [Formula: see text] scale, developed using substituted benzyl radicals, is shown to apply to phenethyl radicals as well.

Substituent effects on benzyl radical hyperfine coupling constants. Part 2. The effect of sulphur substituents

1984 ◽  
Vol 62 (6) ◽  
pp. 1164-1168 ◽  
Author(s):  
Danial D. M. Wayner ◽  
Donald R. Arnold
Keyword(s):  
Electron Spin Resonance ◽  
Spin Density ◽  
Oxidation State ◽  
Esr Spectroscopy ◽  
Hyperfine Coupling ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Benzyl Radical ◽  
Spin Resonance ◽  
Benzyl Radicals

Several 4-substituted benzyl radicals of the general form R(On)SC6H4CH2•(n = 0, 1, 2; R = Me, Ph, Tol, COCH3 OCH3) have been investigated by electron spin resonance (esr) spectroscopy. In general, the ability to delocalize spin density onto the substituent decreases as n increases. The effect of R on the spin density depends on the oxidation state of the sulphur. These trends are explained by considering the sulphur to be either a spin donor or a spin acceptor, depending on the oxidation state. The σ•α values are determined.

Substituent effects on benzyl radical hyperfine coupling (hfc) constants. Part 3. Comparison of the α-hfc for substituted benzyl radicals with the β-hfc for substituted cumyl radicals

1985 ◽  
Vol 63 (5) ◽  
pp. 1150-1155 ◽  
Author(s):  
Donald R. Arnold ◽  
A. Martin De P. Nicholas ◽  
Miles S. Snow
Keyword(s):  
Hyperfine Coupling ◽  
Linear Regression Analysis ◽  
Substituent Effects ◽  
Esr Spectra ◽  
Charge Effects ◽  
Benzyl Radical ◽  
Spin Resonance ◽  
Benzyl Radicals ◽  
Spin Delocalization ◽  
The Relationship

The electron spin resonance (esr) spectra of eighteen para-substituted cumyl radicals were analyzed. The relationship between the β-hyperfine coupling (β-hfc) constants of these cumyl radicals and the corresponding α-hfc constants of benzyl radicals was studied. Although there is a general trend for the α- and β-hfc values to vary in a similar manner, specific deviations from a linear correlation between these parameters were observed. These deviations were rationalized by considering charge effects on spin delcoalization. The correlation coefficient for the linear regression analysis of these α- and β-hfc values was found to significantly improve when β arameters reflecting charge effects on spin delocalization were included in an extended Hammett treatment of the spectral data.

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