MICROWAVE SPECTRA AND INTERNAL ROTATION OF 4-FLUOROPHENOL, 4-CHLOROPHENOL AND 4-BROMOPHENOL

Article abstract of DOI:10.1016/0022-2860(86)80169-7

The microwave spectra of 4-fluorophenol, 4-chlorophenol and 4-bromophenol are analysed in the frequency region 18-40 GHz.The vibrational ground state with two torsional sublevels are assigned for the following molecular species: 4-F-C6H4OH(I), 4-F-C6H4OD(II), 4-(35)Cl-C6H4OH(III), 4-(37)Cl-C6H4OH(IV), 4-(35)Cl-C6H4OD(V), 4-(79)Br-C6H4OH(IV) and 4-(81)Br-C6H4OH(VII).The spectra consist of μ_a- and μ_b-lines.The μ_b-lines appear as doublets with approximately constant splittings of 354 MHz(I), 2.25 MHz(II), 159 MHz(III and IV), 0.75 MHz(V) and 139 MHz(VI and VII).The μ_a-lines are unsplit except for I in which a few μ_a-lines appear as closely spaced doublets.Coriolis type interaction between the torsional substates was observed for I and was proved to be responsible for the splitting of the μ_a-lines.Assuming a semirigid model the effective twofold barriers to internal rotation of the hydroxyl group are calculated to be 1006 cm^-1(I), 1035 cm^-1(II), 1148 cm^-1(III and IV), 1179 cm^-1(V) and 1172 cm^-1(VI and VII).All the molecules are shown to be planar and structural information about the OH group has been obtained for I and III.