Synthesis, spectral characterisations of 3t-pentyl-2r,6c-diarylpiperidin-4-one oxime picrates: DFT studies and potent anti-microbial agents

Abstract

In this paper, various substituted 3t-pentyl-2r,6c-diarylpiperidin-4-one oxime picrates were synthesised and characterised by elemental analysis, FT-IR, NMR, UV–Visible and Fluorescence spectral techniques. For compound 1, NMR spectral assignments were made unambiguously by their one-dimensional (1H and 13C NMR) and two-dimensional (1H–1H COSY, NOESY, HSQC and HMBC) spectra. The observed chemical shifts and coupling constants suggest that compounds 1–7 adopt normal chair conformation with the equatorial orientation of all the substituents like aryl group at C(2) and C(6) and pentyl group at C(3). Compounds 2 and 7 exhibited potent anti-bacterial activity and fungal activity against all the tested strains while all the other compounds showed moderate activity. The molecular structure of compounds (1–7) was optimised at the density functional theory (DFT)/B3LYP/6-311++G(d,p) level of basis set. The calculated first hyperpolarisability (β 0) values show that all the molecules might have non-linear optical (NLO) behaviour. The HOMO–LUMO transition implies that intra-molecular charge transfer takes place within the molecule. The molecular electrostatic potential (MEP) surface is used to understand the reactive sites of a molecule.