Vibrational assignment and structure of dibenzoylmethane. A density functional theoretical study.

Molecular structure and vibrational frequencies of 1,3-diphenyl-1,3-propanedione, known as dibenzoylmethane (DBM), have been investigated by means of density functional theory (DFT) calculations. The results were compared with those of benzoylacetone (BA) and acetylacetone (AA), the parent molecule. IR and Raman spectra of DBM and its deuterated analogue were clearly assigned. The calculated hydrogen bond energy of DBM is 16.15 kcal/mol, calculated at B3LYP/6-311++G** level of theory, which is 0.28 kcal/mol more than that of AA. This result is in agreement with the vibrational and NMR spectroscopy results. The molecular stability and the hydrogen bond strength were investigated by applying the Natural Bond Orbital analysis (NBO) and geometry calculations. The theoretical calculations indicate that the hydrogen bond in DBM is relatively stronger than that in BA and AA.

Structural, IR, and EPR studies of the bis(methoxyacetato)diaquo-copper(II) complex.

The structure, stability, and the IR, and EPR spectroscopic properties of bis(methoxyacetato)diaquo-copper(II) were studied both experimentally using FT-IR and theoretically using B3LYP/6-31G**, B3LYP/6-311G, BWP91/6-31G** methods. The same approaches were used to calculate the harmonic frequencies and to compare them to the experimental solid state values. The g-tensors are calculated using the NMR/GIAO computational method.

Conformational stabilities, infrared, and vibrational dichroism spectroscopy studies of tris(ethylenediamine) zinc(II) chloride.

The conformational stabilities of the transition metal complex of Zn (en)3Cl2 were studied using density functional theory (DFT). Deformational potential energy profiles (PEPs), and pathways between the different isomeric conformational energies were calculated using DFT/B3LYP/6-31G. The relative conformational energies of Delta(lambdalambdalambda), Delta(lambdalambdadelta), Delta(lambdadeltadelta) and Delta(deltadeltadelta) are 10.48, 7.08, 3.56, and 0.0 kcal/mol, respectively, which are small compared to the barrier heights for reversible phase transitions (49.56, 49.55, 49.52 kcal/mol, respectively). Frequency assignment was carried out by decomposing Fourier transform infrared (FTIR) spectra using Gaussian and Gaussview. The theoretical IR and vibrational dichroism spectroscopy (VCD) absorption spectra are presented for all conformations within the range of 400-3,500 cm(-1).

Density functional theory and Møller-Plesset studies of hindered rotations of acetone.

The hindered rotations of acetone were studied density functional theory (B3LYP) and second order Møller-Plesset approaches using 6-31G** and 6-311G** basis sets. One of the CH(3) groups of acetone with fixed heavy atoms was rotated from 0.0 to 120 degrees, and CCH angles were scanned from 90.3 to 130.3 degrees to cover the potential energy surface of interest; a circular valley was obtained with the deepest potential value at a CCH angle equal to 109.3 degrees. Potential energy profiles were then calculated by assuming that the molecular geometry could relax during rotation (i.e., each value of the torsion angle of the molecular geometry was optimized). Next, the two methyl groups were both rotated clockwise, and then one was rotated clockwise and the other counterclockwise. Using the variation method, and utilizing the first 20 harmonic oscillator wave functions, the energy levels, relative transition moment and relative transition intensities of the component of the hindered rotation nu(2) (125.16 cm(-1)) were computed in a one-dimensional Schrodinger equation. The first three energy levels were almost degenerate; the next three were opened up, and the seventh energy level appeared above the level where tunneling can occur.