Microwave spectra and molecular structures of rotational isomers of fluoroacetic acid and fluoroacetyl fluoride

The molecular structures of both the trans- and the cis-conformations of fluoroacetic acid and fluoroacetyl fluoride have been redetermined from the microwave spectra of isotopically substituted species. For the fluoride the results of single and multiple D-substitutions are compared, and the effect of the torsional motion on substitution coordinates is discussed.From the fairly large geometry differences between rotational isomers the energy effect involved in geometry relaxation is estimated to be roughly 1–2 kcal mole^?1 , which is more than the cis-trans energy differences themselves.