Raman and IR studies of isomerization and self-association of β,β′-dichloropivalic acid

• Published in: Vibrational spectroscopy 1998-09, Vol.17 (2), p.163-171
• Main Authors: Mikulskien≐, B, Šablinskas, V, Balevičius, V, Dikčius, G, Kimtys, L
• Format: Article
• Language: English
• Subjects: Carboxylic acids; Hydrogen bonding; Plastic crystals; Vibrational spectrometry
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/S0924-2031(98)00028-9

Processes of conformational changes, hydrogen bonding and phase transitions of β,β′-dichloropivalic acid have been studied by means of Raman and IR spectroscopy, and quantum chemistry (ab initio, semi-empirical AM1 and PM3) calculations. Both the AM1 and PM3 as well as ab initio methods give the conformer with eclipsed C–C and CO bonds ( cis conformer) as the lowest energy conformer. They also predict the trans conformer to be rather stable (Δ E=0.2–0.9 kJ/mol). The enthalpy differences calculated from experimental IR spectra of β,β′-dichloropivalic acid solution in C 2Cl 4 are 52±4 kJ/mol and 22±5 kJ/mol for the monomer↔cyclic dimer and open dimer↔cyclic dimer equilibria, respectively. The high temperature solid phase of β,β′-dichloropivalic acid is found to be a plastically crystalline phase, and this phase is formed on cooling of the melt only. A description of the molecular motion of β,β′-dichloropivalic acid in the melt as well as in the high temperature solid phase in terms of rapid isotropic reorientations is appropriate.