A Note on the Fluorine Resonance Shifts

Abstract

A theoretical analysis is given of the fluorine magnetic resonance shifts in molecules. It is shown that the large range of shifts among different fluorine compounds arises from the effects of binding on the magnetic fields at the nucleus produced by the orbital motion of the electrons in the unfilled valence shell. The simple dependence on ionic character of the bond is also explained. The chemical shift between F2 and HF is calculated to be 14XHr 4 compared to the experimentally observed value 6.3X10-4 •

A 14N nuclear magnetic resonance study on nitrogen–oxygen–halogen compounds

“…TABLE I1 I4N-19F spin-spin interaction Interpretation of 14N chemical shifts (1,4,5) have stressed the dominant role played by the paramagnetic contribution to the chemical shift. This contribution o, is directly proportional to l/AE, where AE is the excitation energy from the electronic ground state to excited states (26,27). The most accessible excited states for the first group of compounds arise from n, -> x* and n, -t o* transitions.…”

Étude théorique de la structure du phosphate d'isaxonine

“…Par contre, la corrtlation est d'une bonne qualitt si l'on considkre seulement les protons de I'hCttrocycle ( r = 0,969 en CND0/2; r = 0,984 en CNDO/S) pour lesquels l'effet des charges sur les deplacements chimiques provient essentiellement des charges 7~ ( r = 0,964 en CND0/2; r = 0,974 en CNDO/S). L'impossibilitt de correler les dtplacements chimiques de tous les protons avec les densites de charge provient du fait que celles-ci n'interviennent que pour une part dans l'expression de la constante d'kcran (17)(18)(19)(20). ou a, est l'effet dii aux charges, acc l'effet dii au courant de cycle, u c~ l'effet dO aux doublets non partagts, a , l'effet dO 2 l'anisotropie des hCtCroatomes et enfin as,,v, est l'effet dri B la solvatation.…”

“…Ceci a pour effet de dirninuer la valeur du terrne d'tcran paramagnttique (16). De plus la protonation tlirnine les niveaux de basse Cnergie associts aux doublets libres des atornes d'azote ce qui augrnente l'tnergie rnoyenne d'excitation et dirninue encore la contribution pararnagnttique (16,17). Ces deux effets conduisent a prtvoir pour tous les atornes de carbone un dkplacernent vers les champs forts constcutif a la protonation.…”

13C Fourier Transform Nuclear Magnetic Resonance. XI. Pyridine N-Oxide Derivatives

“…I3C chemical shifts have been shown to be an effective means for calculation of electron densities and vice versa. The sensitivity of the method derives from the fact that in the 13C shielding constant tensor (8) the paramagnetic term, up, dominates, hence, the large dispersion of I3C shifts results.…”