Infrared and nuclear magnetic resonance studies of rotational isomerism in some acid fluorides

Abstract

From the temperature dependence of the statistically averaged proton–fluorine spin–spin coupling constant 〈J〉_T, the coupling constants associated with and the enthalpy difference between the stable isomers of a number of mono- and di-substituted acetyl fluorides have been determined by a least-squares method. J_HF^trans and J_HF^gauche were found to be of opposite sign in these molecules but the enthalpy differences determined were more comparable with the corresponding gas-phase values than with the liquid-phase value of 8·25 kJ mol^–1 for chloroacetyl fluoride obtained from intensity studies of i.r. bands.