Fourier transform infrared and FT-Raman spectral analysis and ab initio calculations for 4-chloro-2-methylaniline and 4-chloro-3-methylaniline

The Fourier transform infrared (FTIR) and FT-Raman spectra of 4-chloro-2-methylaniline and 4-chloro-3-methylaniline have been recorded in the range 4000–400 and 4000–100 cm−1, respectively. The complete vibrational assignment and analysis of the fundamental modes of the compounds were carried out using the observed FTIR and FT-Raman data. The vibrational frequency which were determined experimentally are compared with those obtained theoretically from ab initio HF and DFT gradient calculations employing the HF/6-31G∗∗ and B3LYP/6-31∗∗ methods for optimised geometries of the compounds. The geometries and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The normal coordinate analysis was also carried out on the basis of ab initio force fields utilising Wilson’s FG matrix method. The interactions of NH–π and the influence of bulky chlorine and methyl group on the vibrational mode of the amino group are investigated.