Molecular Structure, Spectroscopic (UV-Vis, FT-IR and NMR), Conformational Aspects of Some 3t-pentyl-2r,6c- diphenyl/di(thiophen-2-yl)piperidin-4-ones and their Oximes: A Comprehensive Experimental and DFT Study

The geometries and relative energies of 3t-pentyl-2r,6c-diphenyl/di(thiophen-2-yl)piperidin-4ones (PIPs) and their oxime derivatives (PIPOXIs) have been investigated. The structural and spectroscopic analyses of PIPs and PIPOXIs were made by using B3LYP level with 6-311G(d,p) basis set. The optimized parameters show that the piperidi-4-one ring adopts chair conformation. Observed chemical shifts were correlated with calculated values using Gauge-independent atomic orbital (GAIO) density functional theory B3LYP including 6-311+G(2d,p) level theory. Results from the optimized parameters and NMR chemical shifts show that the syn conformations of 2a and 2b are thermodynamically more stable with the oxime group anti to pentyl group. The B3LYP infrared spectra were also computed for the PIPs and PIPOXIs and compared with the experimental spectra. The NBO analysis helps to discover the charge delocalization and E (2) energies confirm the occurrence of intra-molecular charge transfer within the molecule. The electronic transitions states were investigated computationally by applying TD-DFT/B3LYP method using 6-311G(d,p) level theory and show good agreement with the experimental data. In addition, HOMO-LUMO and Non-liner optical property were evaluated by the B3LYP/6-311G(d,p) level theory.