Conformational analysis and structure of cyclopentylcarboxylic acid fluoride

The conformational analysis of cyclopentylcarboxylic acid fluoride was investigated by ab initio methods. The results indicate that, the molecule may exist in one of nine possible conformers, determined by three low-frequency anharmonic vibrations. The twist-gauche and the twist-trans conformers were determined, by all basis sets, to be the most stable conformations for the molecules with the twist-gauche being the lowest-energy conformers at room temperature. The structure optimization of the lowest energy twist-gauche conformer was carried out at the 3-21G, 4-31G and 6-31G levels of calculation. The calculated structural parameters are compared to those obtained from microwave data for cyclobutylcarboxylic acid fluoride in the equatorial -gauche conformation. The calculated differences in bond distances and angles are consistent with the lessstrained five-membered ring in cyclopentylcarboxylic acid fluoride.