Molecular structure, vibrational spectra, HOMO, LUMO and NMR studies of 2-chloro-4-nitrotoluene and 4-chloro-2-nitrotoluene.

The solid phase FTIR and FT-Raman spectra of 2-chloro-4-nitrotoluene (2Cl4NT) and 4-chloro-2-nitrotoluene (4Cl2NT) were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The fundamental vibrational frequencies and intensities of the vibrational bands were evaluated using density functional theory (DFT) with B3LYP method and standard 6-31G* basis set combinations. The infrared and Raman spectra were also predicted from the calculated intensities. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The calculated HOMO and LUMO energies showed that charge transfer had occurred within the molecule. Comparison of simulated spectra with the experimental spectra provided important information about the ability of the computational method to describe the vibrational modes. (13)C NMR chemical shifts results were also compared with the experimental values.