Comparative studies in the 19F and 1H NMR chemical shifts in 2,2-difluorohalogenated propanes

Abstract

Fluorine-19 chemical shifts were compared with 1H chemical shifts in C F 3-CF 2-R versus C H 3-CF 2-R, C F 2Cl-CF 2-R versus C H 2Cl-CF 2-R and C FCl 2-CF 2-R versus C HCl 2-CF 2-R, where R is a substituted methyl group containing all combinations of H, Cl and F. A good linear relationship was found between the 19F and 1H NMR chemical shifts. Conformational analysis using MNDO calculations was applied to the CF 3-CF 2-R and CH 3-CF 2-R series to clarify the interaction between the terminal substituents. In halogenated propanes, 19F and 1H chemical shifts are mainly affected by the through-space interaction between the terminal substituents rather than the electronegativity.