Vibrational Study and Force Field of the Citric Acid Dimer Based on the SQM Methodology

Laura Cecilia Bichara,Evelina Gloria Ferrer,Mónica Beatriz Gramajo,Hernán Enrique Lanús,Silvia Antonia Brandán

doi:10.1155/2011/347072

Laura Cecilia Bichara, Evelina Gloria Ferrer + Show 3 more

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https://doi.org/10.1155/2011/347072

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Abstract

We have carried out a structural and vibrational theoretical study for the citric acid dimer. The Density Functional Theory (DFT) method with the B3LYP/6‐31G∗ and B3LYP/6‐311++G∗∗ methods have been used to study its structure and vibrational properties. Then, in order to get a good assignment of the IR and Raman spectra in solid phase of dimer, the best fit possible between the calculated and recorded frequencies was carry out and the force fields were scaled using the Scaled Quantum Mechanic Force Field (SQMFF) methodology. An assignment of the observed spectral features is proposed. A band of medium intensity at 1242 cm-1 together with a group of weak bands, previously not assigned to the monomer, was in this case assigned to the dimer. Furthermore, the analysis of the Natural Bond Orbitals (NBOs) and the topological properties of electronic charge density by employing Bader′s Atoms in Molecules theory (AIM) for the dimer were carried out to study the charge transference interactions of the compound.

Highlights

The structural and vibrational studies of citric acid are of chemical, biochemical, and technological interest [1–8]
The aim of this paper is to report a Density Functional Theory (DFT) theoretical and experimental study of dimer citric acid by infrared spectroscopy in order to effect a complete assignment of every observed bands in the vibrational spectra by taking into account the presence of the dimeric species in the solid phase
Such observation might mean that the dimer presence even in the gas phase is preferable to the isolated monomer, as observed in the 4-hydroxybenzoic acid dimer [36]

Summary

Introduction

The structural and vibrational studies of citric acid are of chemical, biochemical, and technological interest [1–8]. The aim of this paper is to report a DFT theoretical and experimental study of dimer citric acid by infrared spectroscopy in order to effect a complete assignment of every observed bands in the vibrational spectra by taking into account the presence of the dimeric species in the solid phase. For this purpose, the optimized geometries and frequencies for the normal vibration modes, considering the dimer with two units of the free acid, were calculated. The dimer electronic properties were evaluated by NBO [21,22,23,24] and Atoms in Molecules (AIMs) [25, 26] studies in order to analyze the nature and magnitude of the intermolecular interactions

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