Internal methyl rotation and molecular structure of trifluorotoluenes: microwave rotational spectra of 2,3,4- and 2,4,5-trifluorotoluene

Abstract

The microwave rotational spectra of 2,3,4- and 2,4,5-trifluorotoluenes, along with all13C isotopic species in natural abundance, have been recorded in the frequency range 8–27 GHz employing pulsed-jet Fourier transform microwave spectroscopy. The analysis of the spectra in the lowest torsional state has yielded the rotational constants, centrifugal distortion constants, three-fold barrier to methyl rotation, and the direction of the internal rotation axis in the moment of inertia principal axes systems of these trifluorotoluenes. For both molecules, the molecular constants of their eight isotopologues have been used to obtain the substitution rsstructures of the ring and the methyl-carbon. The potential barriers hindering the internal rotation of the methyl top in 2,3,4- and 2,4,5-trifluorotluene are 2.5878(80) and 2.2809(23) kJ/mol, respectively.