Issue 24, 1993

Conformers, vibrational spectra and infrared-induced rotamerization of dichloroacetic acid in argon and krypton matrices

Abstract

The results of a combined study of dichloroacetic acid monomer undertaken by matrix-isolated low-temperature infrared spectroscopy in both argon and krypton matrices and ab initio SCFMO calculations are presented. Two s-cis(C—O) conformations of CCl2HCO2H differing by internal rotation about the C—C bond and one s-trans form were found in the matrices. Their spectra are reported within the range 4000–400 cm–1 and interpreted. The skew/s-cis form (H—C—C[double bond, length as m-dash]O dihedral angle equal to ca. 144°) converts to the most stable syn/s-cis conformer (H—C—C[double bond, length as m-dash]O: 0°) upon irradiation in the ν(O—H) region. The temperature dependences (annealing) of the isolated matrix vibrational spectra of the studied molecule before and after irradiation were found to be different, and a model is proposed to explain the experimental observations.

In addition, 3-21G and 6-31G*ab initio- MO calculations were carried out and the structures and energies of the relevant conformations are reported. The theoretical results agree with the experimental data and provide a good insight into the intramolecular interactions which determine the relative stability of the various conformers. Finally, a normal-mode analysis based on the 6-31G* harmonic force fields is used to review previous assignments of the vibrational spectra of the various conformers of the studied molecule.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans., 1993,89, 4257-4266

Conformers, vibrational spectra and infrared-induced rotamerization of dichloroacetic acid in argon and krypton matrices

A. Kulbida and R. Fausto, J. Chem. Soc., Faraday Trans., 1993, 89, 4257 DOI: 10.1039/FT9938904257

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