Vibrational conformational analysis of methyl fluoroacetate and methyl difluoroacetate

Abstract The ab initio calculations at 6–31G level predict two stable conformers for methyl fluoroacetate and for methyl difluoroacetate. For both compounds these are the s-cis,trans and s-cis,gauche conformers, with the gauche dihedral angle substantially different from the ideal value. For both compounds the vibrational spectra of the fluid phases show that two conformers are present. The polarity differences calculated by ab initio , together with the ab initio vibrational frequencies allow the observed vibrational bands to be assigned to the predicted conformers. Thermal studies indicate that for methyl fluoroformate in the liquid phase the s-cis,trans conformer is the more stable, while for methyl difluoroformate the s-cis,gauche is the more stable conformer.