Microwave spectrum, structure, dipole moment, and internal rotation of fluoromethyl methyl ether

Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The r_s structure of this molecule was determined from the observed moments of inertia. Structural parameters obtained for this molecule, which was in the gauche form, were compared with those of the analogous molecules. Dipole moments of the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment is 1.744 ± 0.029 D making an angle of 100°54′ with the O---CH₂ bond toward the C---F direction and lies in the plane whose dihedral angles with the FCO and COC planes are 114°9′ and 44°56′, respectively. The barrier to internal rotation of the methyl group was calculated taking into account the coupling effect with the skeletal torsion using the observed splitting data of the spectra in the ground, first excited methyl torsional, and skeletal torsional states. The barrier, skeletal torsional frequency, and coupling term were determined to be V₃ = 1538 ± 40 cal/mole, ω_t = 158 ± 4 cm⁻¹, and V_s = 490 ± 500 cal/mole, respectively.