MOLECULAR GEOMETRIES AND VIBRATIONAL-SPECTRA OF PHENOL, BENZALDEHYDE,AND SALICYLALDEHYDE - EXPERIMENTAL VERSUS QUANTUM-CHEMICAL DATA

Geometric and vibrational spectroscopic data (rotational constants, bo nd distances and angles, vibrational frequencies, IR intensities, and OH/OD isotope effects) of phenol, benzaldehyde, and salicylaldehyde as calculated at various levels of theory (HF/6-31G(d,p), HF/6-311++G(d, p), MP2/6-31G(d,p), B3P86/6-31G(d,p), BLYP/6-31G(d,p), B3LYP/6-31G(d,p ), and B3LYP/6-311++G(d,p)) are reported. The theoretical results are discussed mainly in terms of comparisons with available experimental d ata. For geometric data (rotational constants and bond distances) the best agreement between theory and experiment is obtained at the MP2 an d B3LYP levels. B3P86 calculated data are slightly worse, while HF and BLYP calculations yield distinctly too small and too large bond dista nces, respectively. B3LYP calculated vibrational spectroscopic data ex cellently agree with experimental IR spectra for phenol, phenol-OD, an d benzaldehyde, and with minor restrictions, also for salicylaldehyde and salicylaldehyde-OD. Considering frequency sequences, IR intensitie s, and OH/OD isotope effects, reliable and consistent assignments are given. BLYP and B3P86 calculated vibrational spectroscopic data are sl ightly worse, whereas MP2 and HF calculations suffer from several shor tcomings that are already known from calculations of smaller molecules , such as benzene.