Experimental and theoretical studies on molecular and vibrational structure of 1,2,4,5-Tetracyanobenzene (TCNB)
have been undertaken in the present work. The FT-IR spectrum and FT Raman spectrum of TCNB were recorded respectively in the region 4000–400 cm−1 and 2500-400 cm-1. The optimized geometries in the ground state were calculated by DFT (B3LYP) methods with 6-311G basis set. The optimized structural shown the difference in the bond lengths and some angles are very little affected with a small reduction. The computational results indicate that the molecule adopts a plane geometry and belongs to the D2h point group with the aromatic ring lying in the plane of symmetry. The molecular electrostatic potential shown that the two protons of TCNB as well as the benzene ring are in electron deficient region whereas the CN group are in electron rich region. The carbon atom of CN group and the carbon on the benzene ring are in antibonding interactions in HOMO and in bonding interactions in the LUMO. The harmonic vibrational frequencies, infrared intensities and Raman activities of the TCNB were evaluated. After scaling, the computational wavenumbers are in agreement with the experimental values. A detailed interpretation of the infrared and Raman spectra of TCNB is presented.

Tetra-Cyanobenzene, DFT Calculations, Symmetry