The study of the indirect spin-spin coupling constants Jcl3--H and Jc13-F, deriaed ,from proton and fluorine magnetic resonance spectra, leaded to the conclusion that whereas the Jc13-H data reflect rather truly the state of hybridization of the carbon atom in the C-H bonds (l), the J ~1 3 -F values ure not only influenced by the hybridization of the carbon atom, but also by the ionic character and the double bond character of the C-F bond (".
In a previous paper (3) we commented J~13-F values in systems with sp3 hybridized carbon. Recently we recorded (*) independently froin preiious workers tw>o systems with juorine bonded to an sp2 hybridized curbon atom : acetyljhoride, CH3COF (l), and hexafluorobenzene, C6F6, (11). For (I) our mean value j o r J&3-F, 353 cps, agrees perfectly with Mullers one (2). The C13 satillite spectrum of (11) (**) is ruther complex and can best be described as resulting from the assumed case A& where X is the fluorine atom bonded to C13 (4). On both sides of the main fluorine resonance signal there were obserred tM'o n,eak unconipletely resolved multiplets due to the C13 splitting. The separution of the centers of these was measured and taken as Jc13-F. The ralue found, 362 cps, is rather unexpected when a comjmrison is made betl.1 een relerwnt Jc'3-H data and analogous Jd3-F data.
Whereas the small diferences of JcL3-H j o r systtms with carbon A 0 of the sp2 type can be explained by minor changes in the per cent (*) The experimental techniques are the same as those used before P). (**) The author thanks prof. A.L. Henne (Ohio State Univ. U . S . A .