Molecular conformational analysis, vibrational spectra and normal coordinate analysis of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene based on density functional theory calculations

• The stable geometry of the compound was identified by conformational analysis.
• SQM force field methodology was performed for unambiguous assignment of vibrational bands.
• NBO analysis, HOMO and LUMO energies confirm that charge transfer occurs within the molecule.
• Molecular ESP map predicts the most attractive site for electrophilic attack.

The conformational behavior and structural stability of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene (TDBE) were investigated by using density functional theory (DFT) method with the B3LYP/6-311++G(d,p) basis set combination. The vibrational wavenumbers of TDBE were computed at DFT level and complete vibrational assignments were made on the basis of normal coordinate analysis calculations (NCA). The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. The infrared and Raman spectra were also predicted from the calculated intensities. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP).

The plot shows that the negative charge is located over the oxygen atoms. These are therefore the points to which an electrophile would be most strongly attracted. There are negative potentials above and below the planes of the phenyl ring, which is interpreted as being due to the π electrons.Figure optionsDownload as PowerPoint slide