Density functional calculations of vibrational wavenumbers, ring puckering, and asymmetric CHO potential functions for cyclobutanecarboxaldehyde: comparative study between theoretical and experimental spectra

The structural parameters and energies of the trans-equatorial and gauche-equatorial conformers of cyclobutanecarboxaldehyde c-C₄H₇–CHO were investigated by quantum mechanical DFT-B3LYP (Density Functional Theory-Becke 3 exchange and Lee-Yang–Parr correlation functional) calculations using 6-311G^** basis set. The potential functions for the CHO asymmetric torsion in the equatorial molecule and for the ring puckering inversion were derived. The vibrational wavenumbers were calculated and the potential energy distributions PED among the symmetry coordinates of the normal modes were computed for the two stable conformers of the molecule. The vibrational assignments on the basis of the calculated PED values were compared to the reported ones from experimental data. The vibrational infrared and Raman spectra of the mixture of the trans-equatorial and gauche-equatorial were plotted and the line intensities were compared to the corresponding experimental ones.