Spin density distributions in some fluorinated radical cations

Abstract

AbstractsA theoretical study of n-electron spin density distributions has been made for a series of fluoro-substituted hydrocarbon radical cations using unrestricted Hartree-Fock theory. Although some of the predicted proton splittings are not in very good agreement with experiment, the overall agreement with experiment can be passed as fairly satisfactory considering the approximate nature of the theory used. The experimental fluorine splittings can be well predicted by using a one-parameter relationship between the isotropic fluorine splitting (aF) and the n-electron spin density (pee) on the attached carbon. I t has been further shown that both pcc and the proportionality constant (Qetr) in the linear relation, are fairly insensitive to the parameter choice.On a fait une ttude thCorique des distributions de la densitC de spin des Clectrons T, pour une strie de cations de radicaux d'hydrocarbures fluoro-substituts avec la mtthode de Hartree-Fock sans restrictions. Bien que quelques-unes des stparations protoniques prtdites ne soient pas en trts bon accord avec les donntes exptrimentales, l'accord gtnCral peut itre considtrt relativement satisfaisant eu tgard a la nature approximative de la thCorie. Les stparations exptrimentales du fluor peuvent Ctre prCdites d'une faGon satisfaisante B l'aide d'une relation a un paramttre entre la separation isotrope du fluor (aF) et la densitt de spin des electrons n(pcc) sur l'atome de charbon attache. On a demontrt que pcc et la constante de proportionnalitt ( Qerf) dans la relation lintaire, sont relativement insensibles au choix du paramttre.Eine theoretische Untersuchung der Spindichteverteilungen der n-Elektronen ist fur eine Reihe von Radikalkationen von fluorosubstituierten Kohlenwasserstoffen mit der unbeschrankten Hartree-Fock-Methode ausgefiihrt worden. Obwohl einige der vorhergesagten Protonaufspaltungen nicht besonders gut mit den Experimentaldaten ubereinstimmen, kann die allgemeine Ubereinstimmung in Beziehung auf die angenaherte Natur der Theorie als verhaltnismassig befriedigend betrachtet werden. Die experimentellen Fluor-. aufspaltungen konnen gut mit einer Einparameterbeziehung zwischen der isotropischen Fluoraufspaltung (aF) und der Spindichte der n-Elektronen (pee) an dem festgesetzten Kohlenstoffatom vorhergesagt werden. Es ist auch gezeigt worden, dass sowhol pcc als auch die Proportionalitatskonstante ( Qefr) in der linearen Beziehung gegen die Wahl des Parameters ziemlich unempfindlich sind.

Fluorine Hyperfine Splittings in the Electron Spin Resonance (ESR) Spectra of Aromatic Radicals. An Experimental and Theoretical Investigation

“…One might expect that Q CF , which arises from a spin polarization mechanism similar to the mechanism that is the origin of the McConnell parameter Q CH and which is known to work well in the description of hydrogen hfcc's, should have the same sign as the negative Q CH . However, some previous studies , of fluorine hfcc's dating to the early 1970s have indicated that positive values might occur, though there has been no uniformity in the literature on this point. Our results seem quite unambiguous on this matter and the question then arises as to why the spin polarization mechanism could lead to a positive contribution to fluorine hfcc's.…”

Matrix elements in all valence electron models

“…Some authors [I 1-13] seem to have overlooked the different nature of these two equations. The practical use of Equation (3) has, on the other hand, led to generally satisfactory descriptions of electronic spectra [14-171, also for transition metals in the conjugated system [18], spin densities [16,[19][20][21][22][23], and problems concerning protonation [24,251. Equation ( l ) , sometimes in conjunction with Equation (3), has been used in the determination of polarization directions [26, 271, optical activity [28,291, and magneto-optical activity [30].…”