Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 3223 - 3232 (1988)
Update date:2022-09-26
Topics:
Pedersen, Jens A.
Electron spin resonance spectra have been obtained from series of 2-substituted anthrasemiquinones and of 3-substituted 1,8-dihydroxyanthrasemiquinones.The proton splittings are consistently assigned by means of linear correlation plots between splitting constants and a substituent-dependent paramater.All lines in the plots of he two series of compounds obey the following linear equation aRi = AixR + aHi where aHi and aRi are the splitting constants at position i before and after the substituent has been added.Ai is the slope of the line for the splittings from position i and xR is a constant characteristic of the substituent R. xR is comparable to the Hammett ? parameter.Electron-donating substituents at C-2 are shown to increase the spin densities at the positions 1 > 6 > 8, and to decrease them at the positions 4 > 3 > 7 > 5, with the strength of the effect indicated.Electron-withdrawing substituents have the opposite effect.Preliminary Hueckel molecular-orbital calculations qualitatively predict the observed correlations, solely by changing the parameter for the resonance integral.
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