Molecular modeling and spectral comparison for the change in methyl position of nitrophenol compounds 2-methyl-4-nitrophenol and 3-methyl-4-nitrophenol: A density functional theoretical study

FT-IR and FT-Raman spectra of 2-methyl-4-nitrophenol (PNOC) and 3-methyl-4-nitrophenol (PNMC) were recorded and analyzed in the solid phase in the region 4000–400 cm−1 and 3500–50 cm−1 respectively. Molecular modeling of the compounds PNOC and PNMC were done by the density functional theoretical (DFT) method using Becke’s three parameter exchange functional combined with the Lee–Yang–Parr correlation functional with 6-31G(d) as basis set. Vibrational assignments of the two compounds have been carried out with the help of Normal coordinate analyses (NCA) followed by the Scaled Quantum Mechanical Force Field calculations (SQMFF). Intra-molecular charge transfer and delocalization within the molecule is confirmed with the aid of natural bond orbital analysis (NBO). PNOC and PNMC are similar compounds with same functional groups, only the position of the methyl group is different. The effect of the position change of the methyl group was interpreted with the vibrational spectra.

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► Molecular modeling of PNOC and PNMC were done by the density functional theoretical (DFT) method.
► Frequency shift of 158 cm−1 in the OH stretching of PNMC indicates strong O−H⋯O interaction.
► The stability of the compound increased as the position of the methyl group is changed.