الخلاصة:
This work ispartof a systematicstudy of the behaviorof the methyl group(CH3)and characterization of C-Se-C angle inbenzene, polycyclique, organoselenide compounds substituted with methyl and halogens and that exhibitlargesymmetry. In this case,we have determined the crystal structure of R-C14H8O2Se-R which are Bis(4-acetylphenyl)selenide, bis(4-chloroacetylphenyl) selenide with R=CH3 ,CH2Cl and C6H7Cl respectively and 2.4.5-trimethoxybenzaldehyde and3.5-dimethoxybenzaldehyde compounds using X-ray diffractionat room temperature (293 K).
In parallel, we haveextensivelystudied the possibilities of GAUSSIAN03 program and calculations basedon density functional theory(DFT) to
find precisely the like lymolecularconformationadopted by the isolatedBis(4-
acetylphenyl)selenide, bis(4-chloroacetylphenyl) selenide, chalcone, 2.4.5-
trimethoxybenzaldehyde et 3.5-dimethoxybenzaldehyde.
DFTmethodcan also calculatethevibrational frequencies, IRintensities,Ramanactivities and thereforeto compare themwith experimental results.
Calculationsbased on B3LYPandMPW1PW91functionals and( 6-311G, 6-31G, 6-
311G, 6-31G(d p) , 6-311G(d p) and Lanl2DZ) basis set giveconformationsof symmetryC1for Bis(4-acetylphenyl)selenide,2.4.5-trimethoxybenzaldehydeandbis(4-chloroacetylphenyl) selenideandsymmetrieCs for 3.5-dimethoxybenzaldehyde, with similar energies minimum.
The assignment ofmodesgive a very good agreement betweencalculated and observed frequencies for in plane and out of plane vibration modes.
