Book Description

The inversion of frontier orbitals of free radicals was studied using density functional theory calculations in Gaussian 09. Comparisons of images of orbitals in GaussView was used to assess the relative positions of singly occupied and doubly occupied orbitals and to determine which was the highest in energy. A variety of organic free radicals were studied including several radical anions and also a neutral radical. It was found that cross-conjugation appears to be a factor in whether or not molecules show SOMO-HOMO conversion. Cross-conjugation is when two unsaturated groups are conjugated to a third unsaturated group but are not conjugated to each other. Formaldehyde was analyzed by vibrational self-consistent field (VSCF) calculations at two different levels of theory, Hartree-Fock (HF) and Möller-Plesset 2nd-Order Perturbation Theory (MP2). The calculations were repeated using three different basis sets, aug-cc-pVnZ, n = 2 − 4. Convergence was observed for the VSCF-PT2 (MP2) frequencies for each of the six normal modes of vibration as the basis set was expanded. There was also good agreement between VSCF-PT2 calculated frequencies and experimental values for frequencies of the modes. The chemical shielding constants were calculated using NMR calculations based on the coordinates at 16 different displacements along the vibrational motions for each of the modes. The average chemical shielding values for each mode were determined using the chemical shielding values at the 16 different displacements from equilibrium and the values of the wavefunctions of the modes of vibration at each different displacement. Another NMR calculation was performed for formaldehyde in its optimized conformation, and then the chemical shielding difference from equilibrium across all the modes was calculated for each atom. The differences were added to the equilibrium chemical shielding values to yield vibrationally corrected chemical shielding values. Corrected shielding constants calculated with basis sets aug-cc-pVTZ and aug-cc-pVQZ were close to experiment. In addition, ethylene and methane were analyzed by VSCF and vibrationally corrected chemical shielding values were calculated for these molecules.