R. Cervellati

The microwave spectrum of N,N-dimethylaniline

Abstract The microwave spectrum of N,N -dimethylaniline shows the presence of low vibrational states associated with the inversion of the NMe 2 group and its torsion about the N-aryl bond. The μ a R -branch lines of the ground and First inversion states show small deviations from rigid-rotor behaviour which are consistent with an energy difference of a few cm −1 between these states. The quantities Δ = I a - I b + I c and Δ c = I a + I b - I c indicate values for the CH 3 NCH 3 angle, α, of 114° and for the angle between the ring plane and that containing the two N-CH 3 bonds, φ, of 27°. The barrier to inversion is in the range 1–3 kJ mol −1

The microwave spectrum and large-amplitude vibrations of N-methylaniline

Abstract Microwave spectra of the normal and amine-deuterated isotopic species of N -methyl-aniline in the ground and some low-lying excited vibrational states have been observed. The inertial defect indicates that the dihedral angle of the N-CH 3 , bond with respect to the ring plane is somewhat less than that for the N—H bonds in aniline. The position of the amino-hydrogen atom is very poorly determined by the isotopic substitution method because of large zero-point effects. The excited vibrational states are consistent with a double-minimum potential for the inversion of the HNCH 3 group and there is some evidence for a lower barrier than in aniline. The excited states of the HNCH 3 torsion indicate a barrier in the range 8 2 −1 to the internal rotation of this group. No splitting of the ground-state lines attributable to the torsion of the methyl group has been observed, which implies a barrier of V 3 > 8 kJ mol −1 .

Inversion and torsion of the NMe2 group in the microwave spectrum of N,N-dimethyl-4-aminopyridine

Abstract The microwave spectrum of N,N -dimethyl-4-aminopyridine has been observed in the temperature range 320–350 K. Effects due to the inversion and torsion of the NMe 2 group have been observed. The results show that the barrier to inversion and degree of non planarity are somewhat lower than in N,N -dimethylaniline. Some details of the computer controlled system used to obtain low resolution microwave spectra are given.

Inversion and torsion of the HNCH3 group in the microwave spectrum of N-methyl-p-fluoroaniline

Abstract A reinvestigation of the microwave spectrum of N -methyl- p -fluoroaniline shows this molecule to have low lying excited vibrational states associated with the inversion and torsion of the HNCH 3 group similar to N -methylaniline. The experimental data indicate a greater tendency towards a planar configuration at the nitrogen atom and a lower barrier to inversion compared to p -fluoroaniline.

r0-structure determination of the HNCH3 group of N-methyl-p-fluoroaniline by microwave spectroscopy

Abstract Low resolution microwave spectra of four isotopic species and high resolution microwave spectra of two isotopic species of N -methyl- p -fluoroaniline have been recorded. The rotational constants obtained by each method were used separately for fitting the structure and the results were compared. The N -methyl- p -fluoroaniline molecule is found to be more nearly planar than aniline and p -fluoroaniline, the out-of-plane angle of the HNCH 3 group being φ = 18° ± 3°.