Combined spectroscopic and DFT studies on 2-chloro-4-nitrotoluene and 4-chloro-2-nitrotoluene

The FT-IR and FT-Raman spectra of 2-chloro-4-nitrotoluene and 4-chloro-2-nitrotoluene have been recorded in the regions 4000–400 and 4000–100 cm−1, respectively. The conformational analyses were performed and the energies of the different possible conformers were determined. The geometry of the most stable conformers of the compounds were optimised with B3LYP method using 6-31G**, 6-311++G** and cc-pVTZ basis sets. The optimised structural parameters of the most stable conformer were used in the vibrational frequency calculations. The Raman intensities were also determined with B3LYP method using cc-pVTZ basis set. The force constants obtained from the B3LYP/6-311++G** method have been utilised in the normal coordinate analysis. The temperature dependence of the thermodynamic properties heat capacity at constant pressure (Cp), entropy (S) and enthalpy change (ΔH0→T) for both the compounds were also determined by B3LYP/6-311++G** method. The total electron density and MESP surfaces of the molecules were constructed by using B3LYP/6-311++G** method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. The influences of chloro and nitro groups on the skeletal modes have been investigated.

► FTIR and FT-Raman investigations of 2-chloro-4-nitrotoluene and 4-chloro-2-nitrotoluene were carried out.
► The most stable geometry of the compounds was identified by conformational analysis.
► Energy, structural and thermodynamical characteristics were determined.
► The electrostatic potential, HOMO and LUMO energies were calculated.
► Effect of nitro and chloro groups on the frequencies of the benzene ring has been analysed.