Vibrational spectra of phenol are calculated with ab initio Hartree-Fock and MP2 methods as well as with density functional theory (DFT) using the 6-31G(d,p) basis set. A clear-cut assignment of the vibrational frequencies is reported on the basis of the potential energy distribution (PED) calculated at the three theory levels. These results are compared with the previously reported ab initio data and with the experiment. Several reassignments are suggested for the phenol modes: OH bend, 9b, 17a, 8a, and 8b. It is demonstrated that the MP2/6-31G(d,p) level fails in predicting the frequencies for two modes, labeled 14 and 4 in phenol. The calculated frequency of the former is about 140 cm -1 too high, and that of the latter is 220 cm -1 too low. Very similar results at the MP2 level have been reported earlier for the corresponding ω 14 and ω 4 in benzene. The HF/6-31G(d,p) method provides incorrect results for the modes related to the OH bend in phenol. It is remarkable that DFT with the BLYP functional gives excellent agreement between the calculated and observed frequencies for phenol. In particular, the modes 4 and 14 are predicted to within 11 and 6 cm -1 , respectively, which confirms the reliability of DFT (BLYP) in reproducing vibrational frequencies.

The infrared spectra of phenol and phenol-OD are thoroughly reinvestigated, to resolve the contradictory assignment of some vibrations. The harmonic frequencies, integrated IR intensities, and potential energy distribution (PED) have been calculated by the B3LYP method with the 6-311++G(df,pd) basis set. The Fourier transform infrared (FT-IR) spectra of phenol and phenol-OD have been measured in carbon tetrachloride and cyclohexane solutions, in the frequency range 3700-400 cm -1 , and the experimental integrated infrared intensities are reported. On the basis of the results obtained, the detailed assignment of all the fundamental modes of Ph-OH and Ph-OD are presented. The study demonstrates that density functional B3LYP is clearly superior to the ab initio Hartree-Fock (HF) and second-order Möller-Plesset (MP2) methods in reliable prediction of the vibrational spectra of phenol. In particular, it is shown that scaling of the B3LYP-calculated frequencies of the CH and OH(OD) stretching vibrations by the scaling factor, derived by Baker et al. [J. Phys. Chem. A 1998, 102, 1412 gives excellent agreement between theoretical and experimental frequencies of these vibrations. Detailed theoretical investigations are performed for these troublesome normal modes in phenol and benzene, which show the largest deviations between the MP2-predicted frequencies and the experimental ones. It has been demonstrated that these modes have almost identical atomic displacements and potential energy distributions in both the molecules. The electron correlation effects and basis set dependences are examined, and the nature of these problematical vibrations in aromatic molecules is discussed.

Three pentacoordinate complexes of the type [Co­(pypz)­X2], where pypz is a tridentate ligand 2,6-bis­(pyrazol-1-yl)­pyridine and X = Cl– (1), NCS– (2), and NCO– (3), have been synthesized, and their structures have been determined by X-ray analysis. The DC magnetic data show a sizable magnetic anisotropy, which was confirmed by high-field high-frequency electron paramagnetic resonance (HF EPR) measurements. Well-resolved HF EPR spectra of high spin cobalt (II) were observed over the microwave frequency range 100–650 GHz. The experimental spectra of both complexes were simulated with axial g tensor components, a very large positive D value, and different E/D ratios. To determine the exact D value for 2 (38.4 cm–1) and 3 (40.92 cm–1), the far-infrared magnetic spectroscopy method was used. Knowledge of the zero field splitting parameters and their signs is crucial in interpreting the single-molecule magnet or single chain magnet behavior. The AC susceptibility data confirm that these complexes exhibit a slow magnetic relaxation under small applied DC field with two (1 and 3) or three (2) relaxation modes.

Theoretical studies are performed on enflurane (CHFCl-CF 2 -O-CHF 2 ) to investigate the conformational properties and vibrational spectra. Calculations are carried out at the B3LYP/6-31G(d) level along with a natural bond orbital (NBO) analysis. Experimental infrared spectra are investigated in carbon tetrachloride solution at room temperature and in argon matrix at 12 K. In agreement with previously reported data (Pfeiffer, A.; Mack, H.-G.; Oberhammer, H. J. Am. Chem. Soc. 1998, 120, 6384), it is shown that the four most stable conformers possess a trans configuration of the C-C-O-C skeleton and a gauche orientation of the CHF 2 group (with respect to the central C-O bond). These conformations are favored by electrostatic interaction between the H atom of the CHF 2 group and the F atoms of the central CF 2 group. Hyperconjugation effects from the O lone pairs to the antibonding orbitals of the neighboring C-H and C-F bonds also contribute to the stability of the four conformers. The vibrational frequencies, infrared intensities, and potential energy distributions are calculated at the same level of theory for the most stable conformers. On the basis of the theoretical results, these conformers are identified in an argon matrix. The influence of the concentration on the ν(CH) vibrations suggests the formations of higher aggregates in solution. Theoretical calculations are carried out on the enflurane dimer. The results show that the dimer is formed between two enflurane conformers having the largest stability. The dimer has an asymmetric cyclic structure, the two enflurane molecules being held together by two nonequivalent C-H‚‚‚F hydrogen bonds, the C-H bond of the CHFCl group acting as a proton donor, and one of the F atoms of the CHF 2 groups acting as a proton acceptor. The theory predicts a contraction of 0.0014-0.0025 Å of the two CH bonds involved in the interaction along with a blue shift of 30-38 cm -1 of the corresponding ν(C-H) bands, in good agreement with the blue shifts of 35-39 cm -1 observed in an argon matrix.