Abstract
This work deals with the vibrational spectroscopy of O-Anisic acid (OAA) and Anisic acid (AA). The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with standard B3LYP/6-31G** method and basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. The effects of carbonyl and methyl substitutions on the structure and vibrational frequencies have been investigated. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. The13C and1H NMR chemical shifts of the DFA and CA molecules were calculated using the gauge-invariant-atomic orbital (GIAO) method in DMSO solution using IEF-PCM model and compared with experimental data.
Highlights
Aromatic acids have all the properties characteristic of the carboxylic acids of the aromatic series
The global minimum energies obtained by the density functional theory (DFT) structure optimization for O-Anisic acid (OAA) and Anisic acid (AA) are calculated as −535.3530 and −535.3627 Hartrees, respectively
The substitution of OCH3 with COOH group in the OAA and AA leads to strong intermolecular hydrogen bonding and +I effect, respectively
Summary
Aromatic acids have all the properties characteristic of the carboxylic acids of the aromatic series. Benzoic acid derivatives substituted by hydroxyl group or ether containing oxygen atom have active bacteriostatic and fragrant properties. They are typically used in pharmaceutical and perfumery industry. Anisic acid is a part of cresol class antiseptic compounds. It is used as an insect repellent. The vibrational assignments of the compounds can be proposed on the basis of the wavenumber agreement between the computed harmonics and the observed fundamentals. In the SQM approach, the systematic errors of the computed harmonic force field are corrected by a few scale factors which were found to be well transferable between chemically related molecules [4, 9,10,11]. A detailed quantum chemical study will aid in making definite assignments to fundamental normal modes of OAA and AA to clarify the experimental data for these important molecules
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