Article

Theoretical and experimental vibrational spectrum study of 4-hydroxybenzoic acid as monomer and dimer

INQUINOA, CONICET, Instituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, San Lorenzo 456, T4000CAN Tucumán, Argentina.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy (Impact Factor: 2.13). 02/2010; 75(5):1422-34. DOI: 10.1016/j.saa.2010.01.012
Source: PubMed

ABSTRACT Theoretical calculations on the molecular geometry and the vibrational spectrum of 4-hydroxybenzoic acid were carried out by the Density Functional Theory (DFT/B3LYP) method. In addition, IR and Raman spectra of the 4-hydroxybenzoic acid in solid phase were newly recorded using them in conjunction the experimental and theoretical data (including SQM calculations), a vibrational analysis of this molecular specie was accomplished and a reassignment of the normal modes corresponding to some spectral bands was proposed. The geometries of monomers and dimers in gas phase were optimized using the DFT B3LYP method with the 6-31G*, D95** and 6-311++G** basis sets. Also, both the vibrational spectra recorded and the results of the theoretical calculations show the presence of one stable conformer for the 4-hydroxybenzoic acid cyclic dimer. The B3LYP/6-31G* method was used to study the structure for cyclic dimer of 4-hydroxybenzoic acid and for a complete assignment our results were compared with results of the cyclic dimer of benzoic acid. A scaled quantum mechanical analysis was carried out to yield the best set of harmonic force constants. The formation of the hydrogen bond was investigated in terms of the charge density by the AIM program and by the NBO calculations.

0 Followers
 · 
139 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this work, FT-IR, FT-Raman, UV–Visible andNMRspectroscopies and density functional theory (DFT) calculations were employed to study the structural and vibrational properties of the labdane-type diterpene 13-epi-sclareol using the hybrid B3LYP method together with the 6-31G⁄ basis set. Three stable structures with minimum energy found on the potential energy curves (PES) were optimized, and the corresponding molecular electrostatic potentials, atomic charges, bond orders, stabilization energies and topological properties were computed at the same approximation level. The complete assignment of the bands observed in the vibrational spectrum of 13-epi-sclareol was performed taking into account the internal symmetry coordinates for the three structures using the scaled quantum mechanical force field (SQMFF) methodology at the same level of theory. In addition, the force constants were calculated and compared with those reported in the literature for similar compounds. The predicted vibrational spectrum and the calculated 1HNMR and 13CNMRchemical shifts are ingoodagreement with the corresponding experimental results.Thetheoretical UV–Visspectra for themoststable structure of 13-epi-sclareol demonstrate a better correlation with the corresponding experimental spectrum. The study of the three conformers by means of the theory of atoms in molecules (AIM) revealed different H bond interactions and a strong dependence of the interactions on the distance between the involved atoms. Furthermore, the natural bond orbital (NBO) calculations showed thecharacteristics of the electronic delocalization for thetwosix-memberedrings withchair conformations.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 11/2015; 138:303-313. DOI:10.1016/j.saa.2014.11.049 · 2.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this work we show that the two known polymorphs of 4 0-hydroxyacetophenone (form I, monoclinic, P21/c, Z'/Z = 1/4; form II, orthorhombic, P212121, Z'/Z = 2/8) can be clearly distinguished by diffuse reflectance infrared Fourier-transform infrared (DRIFT) spectroscopy. The experimental studies were complemented by density functional theory calculations (DFT) carried out at the B3LYP/cc-pVTZ level of theory on the E and Z molecular conformers present in the solid forms I and II, respectively. Comparison between the calculated and experimental spectra allowed understanding the influence of polymorphism on the main intermolecular interactions. It was concluded that the differences in the hydrogen bond (H-bond) patterns of the two forms previously highlighted by X-ray diffraction were also captured by the vibrational spectra. Finally, attenuated total reflectance (ATR) spectra suggested that there is a direct connection between the predominant solvent-induced molecular conformation of 4'-hydroxyacetophenone (E or Z) and the selective nucleation of form I from water and form II from ethanol.
    Journal of Molecular Structure 12/2014; 1078:181-187. DOI:10.1016/j.molstruc.2013.11.050 · 1.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have measured the Fourier transform IR spectra of CCl4 solutions of benzoic acid and its biologically active derivatives. We investigated the proton-acceptor properties of the studied molecules theoretically by the molecular electrostatic potential method. The calculations are compared with experimental results. Based on an estimate of the proton-acceptor properties, we give an interpretation of the specific features of the IR spectra of benzoic acid and its derivatives in the region of the O-H and C = O vibrations. The mechanisms for interactions of the molecules are determined by the nature of substituents which are added to the benzene ring in positions para and meta to the carboxyl group. We identify the conditions for appearance of intermolecular hydrogen bonds of O-H center dot center dot center dot O = C, O-H center dot center dot center dot O-H types with formation of cyclic and linear dimers. We show that intramolecular hydrogen bonds of the type O-H center dot center dot center dot O-CH3 prevent the hydroxyl groups from participating in intermolecular interactions.
    Journal of Applied Spectroscopy 03/2014; 81(1-1):109-117. DOI:10.1007/s10812-014-9895-8 · 0.51 Impact Factor

Full-text

Download
7 Downloads
Available from
Mar 3, 2015