AM1 STUDY OF THE CONFORMATIONAL EQUILIBRIUM AND INFRARED-SPECTRUM FOR 1,2,4-SUBSTITUTED AND 1,3,5-SUBSTITUTED BENZENES

The potential energy surfaces (PES) for a series of substituted benzenes 1,2,4-triacetyltriphenylbenzene (I), 1,3,5-triacetyltriphenylbenzene (II), 1,2,4-triacetyltri-n-butylbenzene (III) and 1,3,5-triacetyltri-n-butylbenzene (IV) have been comprehensively investigated using the quantum-mechanical semiempirical method AM1. The semiempirical calculations revealed the existence of distinct equilibrium structures energetically close to the predicted global minimum energy structure for compound II being in satisfactory agreement with the X-ray data. The infrared (IR) spectra have been calculated at the AM1 level and the main absorptions compared to the experimental data showing a good agreement between the theoretical and the observed spectra. These results, therefore, stimulate the semiempirical calculation of vibrational spectra