81689-00-1Relevant academic research and scientific papers
Concerning the Origin of Substituent-Induced Fluorine-19 Chemical Shifts in Aliphatic Fluorides: Carbon-13 and Fluorine-19 Nuclear Magnetic Resonance Study of 1-Fluoro-4-phenylbicyclooctanes Substituted in the Arene Ring
Adcock, William,Abeywickrema, Anil N.
, p. 2945 - 2951 (2007/10/02)
Several 1-fluoro-4-(para-substituted phenyl)bicyclooctanes have been synthesized and their NMR spectra (13C and 19F) recorded.The reverse 19F substituent chemical shifts (SCS) were found to correlate very well with substituent parameters (?I and ?R0) by using the dual substituent parameter (DSP) equation.Linear electric field effects for several substituents were estimated from the ρI?I term for the DSP correlation, and these were employed for calculating the coefficient (A) of the Buckingham equation (SCS = AEz).The negative sign of the Avalue for linear electric field effects on Csp3-F bonds stands in contrast to the positive value for fluorine attached to sp2 carbons.It was also found that the 19F SCS correlate extremely well with the corresponding 13C SCS of the bridgehead carbon (C1) attached to fluorine and with the changes in the one-bond carbon-fluorine spin-spin coupling constants (Δ1JCF).These results reveal that the phenomenon of reverse 19F SCS of aliphatic fluorides is a manifestation of dominant changes in fluorine ?-electron density.The origin of exalted 19F SCS of aliphatic fluorides in trifluoroacetic acid solution has been delineated.
