The experimental theorical investigation of the 2,-4 and 6-bromonikotonic acid molecules by vibrational spectroscopy

The experimental and theoretical study on the structures and vibrations of 2, 4 ve 6-bromonicotinic acid (2, 4 ve 6-BrNA, C6H4BrNO2) are presented. The Fourier transform infrared spectra (4000?400 cm-1 ) and the Fourier transform Raman spectra (4000?0 cm-1) of the title molecule in solid phase have been recorded, for the first time. There are four conformers, C1, C2, C3, C4 and Dimer C1 for this molecule. The molecular geometry and vibrational frequencies of 2, 4 and 6- bromonicotinic acid in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-311++G (d,p) as the basis set. Calculations were carried out using Gaussian 03 package of program. On the basis of the comparison between calculated and experimental geometric parameters of 2 and 6-bromonicotinic acid HF method, B3LYP molecular vibrational problems gives best correlation.