The carbon-13 nuclear magnetic resonance spectra of the deoxyfluoro-D-glucoses, 2-deoxy-2-fluoro-D-mannose, and 4-deoxy-4-fluoro-D-galactose. Orientational and substituent effects upon n J FC

Abstract

A detailed study has been made of the 19C n.m.r. spectra of the anomeric pairs of the deoxyfluoro-D-glucopyranoses, 2-deoxy-2-fluoro-D-mannopyranose, and 4-deoxy-4-fluoro-D-galactose. The variation in 1JFC with the electronegativity of α-substituents is rationalised by consideration of literature data and by the use of a procedure used previously to rationalise 19F chemical shifts. 2JFC is less dependent upon the electronegativity of substituents attached to the coupled fragment but it shows a marked dependency upon the orientation of substituents bonded to the coupled carbon. 3JFC and 4JFC show marked dependencies upon the orientation of the coupled nuclei, and in the former the orientation of substituents upon the coupled fragment is important. INDO MO calculations reproduce the trends in both 3JFC and 4JFC, and rationalise the long-range JFH data obtained previously for these systems. 13C Shifts are discussed briefly.