Temperature Dependence of Torsional Frequencies in Some Dichloro-Anilines Using Nuclear Quadrupole Resonance Data

The temperature variation of the nuclear quadrupole resonance frequencies in 3,4-dichloro-aniline and 2,6-dichloro-aniline were fitted to three different models available in literature, namely the Kushida model, the Brown model, and a fourth order polynomial. Brown's model with T0 = 205 K gave the best fit in the case of both compounds indicating that the temperature dependence of the torsional frequencies cannot be neglected in these compounds. The internal torsional frequencies were evaluated from the nuclear quadrupole resonance data by using a two-mode approximation in a temperature range of 77-300 K for the above two compounds. The torsional frequencies lie in a range of 30-60 cm -1 in both compounds and agree closely with the Raman lines obtained in 2,6-dichloro-aniline. The lower frequency mode around 37 cm-1 may be associated with the motion around an axis perpendicular to the benzene ring which is present in both compounds.