A Density Functional, Infrared Linear Dichroism, and Normal Coordinate Study of Phenol and its Deuterated Derivatives:  Revised Interpretation of the Vibrational Spectra

Abstract

The assignment of the vibrational spectra of phenol has been reexamined on the basis of Raman and new IR measurements and theoretical analysis of the normal modes of vibrations in the electronic ground state. The infrared spectra of C 6 H 5 OH, C 6 D 5 OD, and C 6 D 5 OH have been studied in solution and vapor phases, as well as has the Raman spectra in solutions. New experimental data were obtained from infrared linear dichroism (IR-LD) studies of phenol aligned in uniaxially oriented nematic liquid crystal solution. The measured dichroic ratios and orientation factors indicate an effective C s symmetry of the molecule with coplanar orientation of OH bond with the benzene ring and supply unique information on the extent of symmetry lowering of benzene normal modes. The fundamental vibrational frequencies, force constants, and dipole derivatives have been calculated by ab initio quantum chemical methods applying the B3P86 density functional approximation with 6-311G** basis set. The force field optimized by means of a least-squares scaling procedure for phenold 0 (using six scale factors) was used to calculate the frequencies (with a mean deviation from the observed values less than 1%), normal modes, potential energy distributions, transition moment vectors, and IR intensities for phenol-d 0 , -d 1 , -d 5 , and -d 6 isotopomers. Compared to the deviations between the calculated and observed absorption intensities, a more satisfactory correlation was found between the calculated and experimentally determined Vibrational transition moment directions. The results indicate unanimously that the perturbation of the normal modes of benzene by the asymmetric hydroxyl substituent is so great that the previous practice of assigning the normal vibrations of phenol to those of benzene or even to C 2V symmetry species is not justified.

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

“…Furthermore, the calculated IR spectrum of phenol H3 exhibits a very intense vibration at 1161 cm −1 without matching an experimental band. This vibration has also been obtained by other DFT calculations [93,95,96,98,113]. Despite of some C-C stretch character, this vibration has C-H and O-H in-plane bending character and has been assigned to a strong band at 1177 cm −1 in the IR spectrum of phenol vapor [114,115].…”

Synthesis, thermal study and some properties of N2O4—donor Schiff base and its Mn(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes

“…This band can be due to the presence of free hydroxyl group of acetic acid which was observed for monomer of acetic acid by Maçôas et al [34]. However, it cannot be ruled out that one of the phenolic groups in the para position may not be involved in any hydrogen bonds and also shows vibrations in this region [32,35].…”

A reducing-difference IR-spectral study of 4-aminopyridine

“…OH 2 -hydrogen bond formation [31]. The IR-LD-spectral band study of phenol as 5% (m/m) liquid crystal solution demonstrates a τ -OH band at 620 cm −1 [32] which corresponds to an increase of 310 cm −1 with respect to this frequency in dilute non-polar solvent. As a result of these assumptions the 440 cm −1 peak in the IR-spectra of the solid state 4-AP should be treated as torsional NH 2 -vibration.…”