Spectroscopic (FTIR, FT-Raman, NMR and UV) and molecular structure investigations of 1,5-diphenylpenta-2,4-dien-1-one: a combined experimental and theoretical approach

The title molecule 1,5-diphenylpenta-2,4-dien-1-one (cinnamylideneacetophenone, CA) has been synthesised and characterised by FTIR, FT-Raman, NMR and UVvis spectral analyses. The possible stable conformers of the CA molecule were searched by potential energy surface scan at B3LYP level of theory. The molecular geometry from X-ray determination of the CA molecule in the ground state has been compared using the density functional theory (DFT) with 6-31G(d,p) basis set. The harmonic vibrational modes, the corresponding wavenumbers and IR and Raman intensities of most stable conformer were calculated by the DFT method. The assignments of the fundamentals were proposed on the basis of total energy distribution calculations. The calculated 13C and 1H NMR chemical shifts using gauge including atomic orbitals approach are in good agreement with the observed chemical shifts. The molecular stability and bond strength have been investigated by applying natural bond orbital analysis. Using the time-dependent DFT method, the electronic absorption spectrum of the title compound has been predicted and the electronic transitions within the molecule have been interpreted. The molecular electrostatic potential map was used for predicting possible hydrogen and oxygen bonding sites in the CA molecule.