Vibrational analysis and valence force field for nitrotoluenes, dimethylanilines and some substituted methylbenzenes.

The Fourier transform infrared (FTIR) and Raman spectra of 2-amino-4-nitrotoluene; 2-amino-5-nitrotoluene; 2,4-dimethylaniline; 2,5-dimethylaniline; 2,6-dimethylaniline; 1,2,4-trimethylbenzene; 1,3,5-trimethylbenzene and pentamethylbenzene have been recorded in the range 4000-400 cm(-1) and 4000-30 cm(-1), respectively. A normal coordinate analysis was carried out for both in-plane and out-of-plane vibrations of these molecules using an 81-parameter modified valence force field. The force constants were refined using 369 frequencies of eight molecules in the overlay least-squares technique. The reliability of the force constants was tested by making a zero-order calculation for both in-plane and out-of-plane vibrations for five related molecules. The potential energy distributions and eigen vectors calculated in the process were used to make unambiguous vibrational assignments of all the fundamentals.