Theoretical and Experimental Vibrational Study of Anhydrous Citric Acid as Monomer and Dimer

L. C. BICHARA; E. G. FERRER; H. E. LANÚS; C. G. NIETO; S.A. BRANDÁN

Venecia

Congreso; EUCMOS 2010-30th European Congress of Molecular Spectroscopy; 2010

A new structural and vibrational theoretical study of the anhydrous citric acid as monomer and dimer (Figure 1) was performed employing the Density Functional Theory (DFT) method with Pople’s basis sets. The new vibrational spectra registered in solid state were compared with those obtained for the monohydrated acid. The geometries of monomers and dimer in gas phase were fully optimised at the B3LYP/6-31G*and B3LYP/6-311++G** levels of theory by using the Gaussian 03 program [1] and the harmonic wavenumbers were evaluated at the same levels. For a complete assignment of the vibrational spectra, DFT calculations were combined with Pulay´s Scaled Quantum Mechanics Force Field (SQMFF) methodology [2] in order to fit the theoretical wavenumber values to the experimental ones. In this way, a complete assignment of all the observed bands in the vibrational spectra was performed. The scaled force constants for monomer and dimer species are also reported. The natural bond orbital (NBO) study [3] reveals the characteristics of the electronic delocalization of the dimeric species of the acid while the corresponding topological properties of electronic charge density are analysed by employing Bader’s Atoms in Molecules theory (AIM) [4]. The natural bond orbital (NBO) study [3] reveals the characteristics of the electronic delocalization of the dimeric species of the acid while the corresponding topological properties of electronic charge density are analysed by employing Bader’s Atoms in Molecules theory (AIM) [4]. The natural bond orbital (NBO) study [3] reveals the characteristics of the electronic delocalization of the dimeric species of the acid while the corresponding topological properties of electronic charge density are analysed by employing Bader’s Atoms in Molecules theory (AIM) [4]. The natural bond orbital (NBO) study [3] reveals the characteristics of the electronic delocalization of the dimeric species of the acid while the corresponding topological properties of electronic charge density are analysed by employing Bader’s Atoms in Molecules theory (AIM) [4].