POLARIZED C-H GROUPS AS NOVEL HYDROGEN-BOND DONORS IN HYDRYL-F-ALKYL ESTERS - UNEQUIVOCAL EXAMPLES FOR THE PINCHAS-EFFECT

H-1 NMR and IR spectral evidence for a C-H...O hydrogen bonds in 1-[2-hydryl-F-adamantyl] trifluoroacetate and 1,3-[2-hydryl-F-adamantyl] bis(trifluoroacetate) are presented. Evidence indicating a three-center hydrogen bond in 1,3-[2-hydryl-F-adamantyl] bis-(trifluoroacetate) is also presented. Both compounds, despite otherwise normal H-1 NMR chemical shift displacements and carbonyl stretching frequency depressions, show strong increases in C-H stretching frequencies related to hydrogen-bond interactions (the ''Pinchas Effect'').