Infrared

Trifluoroacetic acid

Physics

Organic chemistry

Optics

Trifluoroacetic anhydride

Chemistry

Infrared spectroscopy

Spectrochimica Acta Part A Molecular Spectroscopy

Spectra of matrix-isolated trifluoroacetic acid species and matrix-isolated and solid trifluoroacetic anhydride are reported. Vibrational assignments are given for the CF3COOH and CF3COOD monomers, the i.r. active vibrations of (CF3COOH)2 and (CF3COOD)2 cyclic dimers, and (CF3CO)2O.The analysis suggests that a very low barrier hinders internal rotation of the CF3 group in the acids and also indicates the probable absence of an equilibrium plane of symmetry in the monomers. The truth of these statements hinges on the interpretation of the data for the nominal COH bending vibration. For CF3COOH monomer this band shows two components that are separated by ~15 cm−1, while CF3COOD monomer yields a single, sharp band that is red-shifted by a normal amount. These observations, coupled with the anomalous isotopic frequency behavior found for this vibration with acetic acid monomers [C.V. Berney, R.L. Redington and K.C. Lin, J. Chem. Phys.53, 1743 (1970)], reinforces the suggestion that a relatively low barrier hinders H atom transfer between the two O atoms via a coordinate that originates as COH angle bending.

Infrared spectra of trifluoroacetic acid and trifluoroacetic anhydride