Spectroscopie, conformation théorique et structure cristalline de quelques produits halogénodurènes

Abstract

This work is part of a systematic study of the behavior of the methyl group (CH3) in benzene compounds C10H13X substituted with methyl and halogens and that exhibit large symmetry. In this case, we have determined the crystal structure of bromodurene (BD) and iododurene (ID) from the X-ray diffraction at room temperature (293 K). Experience show that iododurene (C10H13I) crystallizes in the same space group that the bromodurene (C10H13Br) of the orthorhombic P212121 with four molecules per unit cell. The molecular packing is along the shortest crystallographic axis a. In parallel, we have extensively studied the possibilities of GAUSSIAN 03 program and calculations based on density functional theory (DFT) to find precisely the likely molecular conformation adopted by the isolated durene (C10H14) molecule and its derivatives (X = I, Br, Cl). DFT method can also calculate the vibrational frequencies, IR intensities, Raman activities and therefore to compare them with experimental results. Calculations based on B3LYP and MPW1PW91 functionals and DGDZVP basis set give conformations of symmetry D2h for durene and two symmetries Cs and C2v for chlorodurene (CD). Bromodurene (BD) and iododurene (ID) have similar energies minimum. Experimentally, molecular structures of BD and ID compounds are much closer to that of C2v and Cs obtained from MPW1PW91 / DGDZVP functional. So, calculations of internal modes vibration were undertaken from this functional. Theoretical calculations of IR and Raman spectroscopy allowed the assignment of 66 internal modes of bromodurene and iododurene. The assignment of modes give a very good agreement between calculated and observed frequencies for inplane and outofplane vibration mode