Vibrational spectra, UV–vis spectral analysis and HOMO–LUMO studies of 2,4-dichloro-5-nitropyrimidine and 4-methyl-2-(methylthio)pyrimidine

The FT-IR and FT-Raman vibrational spectra of 2,4-dichloro-5-nitropyrimidine (DCNP) and 4-methyl-2-(methylthio)pyrimidine (MTP) have been recorded in the range 4000–400 and 3600–50 cm−1, respectively. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated using density functional B3LYP method with 6-31+G(d,p) and 6-311++G(d,p) basis set combinations. With the help of specific scaling procedures, the observed vibrational wavenumbers in FT-IR and FT-Raman spectra are analyzed and assigned to different normal modes of the molecules. The predicted first hyperpolarizability reveals that the molecules are an attractive object for future studies of non-linear optical properties. And also HOMO–LUMO energy gap explains the eventual charge transfer interaction taking place within the molecules. UV–vis spectral analysis of the title compounds has been researched by theoretical calculations. The frontier orbital energies, absorption wavelengths (λ), oscillator strengths (f) and excitation energies (E) studied using TD-DFT (B3LYP) with 6-311++G(d,p) basis set are calculated in this work.

The FTIR and FT Raman vibrational spectra of 2,4-dichloro-5-nitropyrimidine (DCNP) and 4-methyl-2-(methylthio)pyrimidine (MTP) have been recorded using BRUKER RFS 100 s−1 spectrometer in the range 4000–400 and 3600–50 cm−1, respectively. A detailed vibrational spectral analysis has been carried out, and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated using density functional B3LYP method with 6-31+G(d,p) and 6-311++G(d,p) basis set combinations. With the help of specific scaling procedures, the observed vibrational wave numbers in FTIR and FT Raman spectra are analyzed and assigned to different normal modes of the molecule. UV–vis spectral analysis of the title compounds has been researched by theoretical calculations. The frontier orbital energies, absorption wavelengths (λ), oscillator strengths (f) and excitation energies (E) studied using TD-DFT (B3LYP) with 6-311++G(d,p) basis set are calculated in this work.Figure optionsDownload as PowerPoint slideHighlights
► A complete vibrational analysis of DCNP and MTP are performed.
► DCNP has the smallest HOMO–LUMO gap.
► DCNP is thermodynamically stable, MTP is more reactive.
► The predicted β value reveals that both molecules are an attractive object for future studies of NLO properties.
► We have found that the conformer 2 (b) is more stable for MTP.