Spectroscopic (FT-IR, FT-Raman, UV and NMR) investigation on 1-phenyl-2-nitropropene by quantum computational calculations

Abstract

In this paper, the spectral analysis of 1-phenyl-2-nitropropene is carried out using the FTIR, FT Raman, FT NMR and UV–Vis spectra of the compound with the help of quantum mechanical computations using ab-initio and density functional theories. The FT-IR (4000–400cm−1) and FT-Raman (4000–100cm−1) spectra were recorded in solid phase, the 1H and 13C NMR spectra were recorded in CDCl3 solution phase and the UV–Vis (200–800nm) spectrum was recorded in ethanol solution phase. The different conformers of the compound and their minimum energies are studied using B3LYP functional with 6-311+G(d,p) basis set and two stable conformers with lowest energy were identified and the same was used for further computations. The computed wavenumbers from different methods are scaled so as to agree with the experimental values and the scaling factors are reported. All the modes of vibrations are assigned and the structure the molecule is analyzed in terms of parameters like bond length, bond angle and dihedral angle predicted by both B3LYP and B3PW91 methods with 6-311+G(d,p) and 6-311++G(d,p) basis sets. The values of dipole moment (μ), polarizability (α) and hyperpolarizability (β) of the molecule are reported, using which the non-linear property of the molecule is discussed. The HOMO–LUMO mappings are reported which reveals the different charge transfer possibilities within the molecule. The isotropic chemical shifts predicted for 1H and 13C atoms using gauge invariant atomic orbital (GIAO) theory show good agreement with experimental shifts. NBO analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. The local reactivity of the molecule has been studied using the Fukui function. The thermodynamic properties (heat capacity, entropy and enthalpy) at different temperatures are also calculated.