THERMODYNAMIC FUNCTIONS OF ROTATIONAL EQULIBRIA IN ETHYL-ACETATE AND MONOHALOACETATES

The integrated intensities of some paired bands of the infrared spectra of ethyl acetate, fluoroacetate and chloroacetate have been measured in cyclohexane solution at different temperatures. Values obtained have been used to calculate ΔHδ of the two rotational equilibria (generated by rotation of the halomethyl group around the CC bond and by rotation of the ethyl group around the OEt bond). Different methods have been used to calculate ΔSδ and the values obtained have been discussed. The components of the split bands were assigned to the expected conformers and used for statistical calculation of the entropy increment. This assignment has been verified using the sum rule of Mizushima and co-workers. Values obtained for ΔHδ and ΔSδ confirm the stability of the trans conformer of all three compounds when rotation of the ethyl group is considered. ΔHδ calculation for the equilibrium between trans and cis (or gauche) rotamers, defined by the rotation of the halomethyl group, predicts different behaviour for each of the two haloacetates studied, in agreement with experimental results. © 1990.