Résumé:
This work presents a continuation of study of the influence of substitution on the conformation of aromatic molecules.
The crystal structure of β -methyl-α dicyanostyréne (C11H8N2) was determined at room temperature by X-ray diffraction The crystal is Orthorhombic with a space group P 21 21 21 and Z = 4. The refinements of the molecule led from the CRYSTALS program. We have shown for a styrene
substituted in position to the vinyl group that their structure is not flat and the predictions of the theoretical calculations by DFT are in agreement with the experimental results, we used the chain GAUSSIAN03 programs.
The first calculation on the fully released molecule leads to another isomer.In the case where the calculations are made with a constraint that requires the double bond C (α ) -C ( β) obtaining a conformation similar to that observed in the crystal but with a double bond this time equal to 1.370 Å .
the calculated length of this bond present in the worse agreement with experiment against other distances. These theoretical calculations predict the conformation of the molecule of -methyl- - dicyanostyréne made clearly show the possibility of achieving several different solutions so that the solution that has the minimum training energy, ie most favorable, do not always correspond to the desired conformation.
IR spectroscopy theoretical calculations allowed the assignment of different modes of ibration
movements of the molecule.
