SYNTHESIS AND F-19 AND C-13 NMR-STUDIES OF A SERIES OF 4-SUBSTITUTED FLUOROCUBANES - RESONANCE DEPENDENCE OF F-19 CHEMICAL-SHIFTS IN A SATURATED SYSTEM

The substituent chemical shifts and the carbon-fluorine coupling const ants of a range of 4-substituted cubyl fluorides in solvents of varyin g polarity are presented. Least squares regressional analysis of the d ata indicates that the fluorine probe, while being somewhat less sensi tive to field effects as a result of the low polarizability of the cub ane C-F bond, nevertheless responds in the ''reverse'' manner in agree ment with precedents established in other alicyclic systems. The depen dence of (1)J(CF) upon electronegativity has been interpreted as evide nce for the occurrence of sigma-induction over four bonds, the longest reported to date. Significantly, resonance parameters are found to be very important in describing the effect of substituents on both the f luorine chemical shifts and the magnitude of the one-bond and four-bon d C-13-F-19 coupling constants. This represents one of the rare occasi ons that resonance effects have been observed in a fully saturated sys tem in the ground state. A possible mechanism by which these resonance effects may be transmitted is presented.