Experimental spectroscopic (FTIR, FT-Raman, FT-NMR, UV–Visible) and DFT studies of 2-amino-5-chlorobenzoxazole

The solid phase FTIR and FT-Raman spectra of 2-amino-5-chlorobenzoxazole have been recorded in the regions 4000–400 and 3500–100 cm−1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the compound was optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets. The molecular properties were also determined by HF/6-311++G(d,p) level. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV–Visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman activities chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule. The influences of chlorine atom and the amino group on the skeletal modes and on the proton chemical shifts have been investigated.