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 nJFC

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 ¹J_FC 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. ²J_FC 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. ³J_FC and ⁴J_FC 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 ³J_FC and ⁴J_FC, and rationalise the long-range J_FH data obtained previously for these systems. ¹³C Shifts are discussed briefly.