Medium ring compounds and their anions: a systematic density functional theory study

The optimized geometries, harmonic vibrational frequencies, and adiabatic electron affinities of eight ring compounds: o-benzyne, cyclohexanone enolate, cyclopentadienyl radical, cyclopentanone enolate, maleic anhydride, phenoxyl radical, phenyl radical, and pyrrolyl radical have been determined with six different density functional or hybrid Hartree-Fock density functional methods using a double-zeta basis set with polarization and diffuse functions (DZP++). The optimized geometric structures are discussed. Harmonic vibrational frequencies were generally found to be within 4% of available experimental fundamentals for most functionals. Of the six functionals, BP86 predicted electron affinities remarkably close to the experimental values for six of the eight molecules studied, with an overall average absolute error with respect to experiment of just 0.12 eV. The B3LYP and BLYP functionals also gave excellent predictions, with absolute average errors of 0.18 and 0.20 eV, respectively.