Etude structurale cristalline et spectroscopique des produits benzéniques méthylés et halogéno-méthylés

Abstract

Within the framework of this thesis, the main interest was to carry a structural and spectroscopic study of the benzene products constituted from methyl and halogens and /or amines diaminomesitylene C9H14N2 and the dibromomethylaniline C7H7Br2. The structure of the diaminomesitylene. (DAM) was obtained from the diffraction of the X-ray on a monocrystal at room temperature. This product crystallizes in the group space P21/c with four molecules per cell. Dibromomethylaniline (DBMA) has been studied at relatively low temperature 200k, and it has an orthorhombic structure P212121, Z=4. The stacking in the two products is realized along the shortest axe crystallographic a. Hirschfield’s surface analysis is generated through the Crystal Explorer program, providing information on the existing interactions in the structure of both products and helping to view and understand its crystalline stack. Hand in hand with the experimental investigation, we have made theoretical calculations on the conformation of the isolated molecule using the DFT (density functional theory) methods, which are well known by their precision. The energy of minimal formation of the molecule obtained on the basis of theoretical calculations results in a molecular conformation which is very close to that obtained by experiments. The optimization calculations of molecular conformation using the chain of ADF program also led to results that are very close to those obtained from the experiment, concerning the length and angles of connection. The computation results starting from functional calculus B3LYP, (BP86) and (TZP) revealed that the conformation of the DAM presents a symmetry Cs while that of DBMA presents a C1 symmetry with a good agreement compared to the results of the X-ray diffraction. The calculations confirm the flatness of the molecule obtained in experiments, as we were able to attribute the majority of the frequencies. The experimental results, showed a very good agreement with DFT calculations for the mode of vibration in and out of the plan of these compounds. In the framework of the functional theory of time-dependent density TDDFT, studies have been carried out to calculate the optical absorption in order to better understand the excitation phenomenon, compared with the experiment.