Experimental and DFT Quantum Chemical Studies on Structural, Vibrational and Molecular Properties of Some Substituted 4-Phenylphenols

Abstract

Fourier Transform infrared spectra (4000–400 cm−1) and Fourier Transform Raman spectra (4000–50 cm−1) were recorded for 2-chloro-4-phenylphenol (CP); 2-nitro-4-phenylphenol (NP); and 2-amino-4-phenylphenol (AP). 1H and 13C NMR spectra, along with UV-Vis spectra of the three samples were also measured. Quantum chemical calculations, at the level of DFT/B3LYP/6-311++G(d,p) theory were implemented to study their ground state geometry, vibrational wave numbers, infrared and Raman intensities, 1H and 13C NMR spectra, frontier molecular orbital parameters, NLO behavior, NBO properties, thermodynamic quantities, rotational constants and MESP behavior. TD-DFT variant was employed to simulate electronic transitions of these molecules. Observed and calculated vibrational frequencies agreed with an rms error 7.44, 8.98 and 6.97 cm−1, the corresponding RMSD values being 7.09, 9.39 and 6.59 cm−1 for CP, NP and AP, respectively. Experimental chemical shifts concurred, with their theoretical counterparts, with RMSD value, 0.19, 0.29 and 0.56 ppm for 1H NMR; and 6.34, 6.28 and 5.39 ppm for 13C NMR, respectively, in CP, NP and AP. This kind of agreement was also true for absorption maxima (λ max) of their electronic transitions in solution form. Frontier molecular orbitals were found useful to understand origin of electronic transition maxima and chemical reactivity of the three molecules which was supported by NBO analyses. The computations showed that the three molecules were potentially good for developing NLO materials. MESP investigations showed that the most reactive sites are at oxygen atoms in the three molecules. Moreover, we also made an attempt to understand the effect of deactivating (Cl, NO2) and activating (NH2) groups on certain properties of the three molecules. Presence of intra-molecular hydrogen bond was predicted in CP, NP and AP.