Microwave and infra-red spectra and conformation of methyl trifluoroacetate

Abstract

The microwave spectrum, between 14 000 and 40 000 MHz, and the infra-red spectrum, between 4000 and 10 cm^–1, have been obtained for methyl trifluoroacetate. The molecular conformation has been found to be planar or near-planar cis(i.e., methyl group cis to the carbonyl group). The dipole moment has been measured at 296 K in benzene solution and found to be 2.70 ± 0.15 D. Some of the infra-red absorption bands have been reassigned to group vibrations, and the potential barriers hindering internal rotation about the CF₃—C and C(O)—O bonds are estimated from the torsional frequencies of the vapour to be 1.93 ± 0.77 kJ mol^–1 and 47.7 ± 2.9 kJ mol^–1 respectively. No evidence was found for the presence of another rotamer.