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.
