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Molecular Structure, Spectroscopic (UV-Vis, FT-IR and NMR ... Molecular Structure, Spectroscopic (UV-Vis, FT-IR and NMR), Conformational Aspects of Some 3 t -pentyl-2 r ,6 c - diphenyl/di(thiophen-2-yl)piperidin-4-ones

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  • Borderless Science Publishing 226

    Canadian Chemical Transactions Year 2016 | Volume 4 | Issue 2 | Page 226-243

    Research Article DOI:10.13179/canchemtrans.2016.04.02.0290

    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

    Mariadoss Arockia doss, Govindasamy Rajarajan*, Venugopal Thanikachalam

    Department of chemistry, Annamalai University, Annamalainagar 608 002, India

    *Corresponding Author, Email: [email protected]

    Received: March 7, 2016 Revised: May 5, 2016 Accepted: May 18, 2016 Published: May 24, 2016

    Abstract: The geometries and relative energies of 3t-pentyl-2r,6c-diphenyl/di(thiophen-2-yl)piperidin-4-

    ones (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.

    Keywords: PIPs and PIPOXISs, FT-IR, GAIO, hyperpolarizability, NBO, HOMO –LUMO.

    1. INTRODUCTION

    Piperidin-4-ones make an interesting group of heterocyclic molecules. The compounds of this

    family exhibit a broad spectrum of pharmacological properties such as antitumor, antibacterial, antiviral,

    antimalarial and antiprotozoal activities [1-4]. Besides these, such compounds have drawn the attention of

    photoscientists because of their huge potential in non- linear optical fields [4,5]. Therefore, the biological

    importance of piperidin-4-one and its oxime has strongly stimulated the investigation of computational

    properties available for these compounds. DFT calculations provide accurate results on systems such as

    large organic molecules [6]. Following our studies on thiosemicarbazone and semicarbazone group in

  • Borderless Science Publishing 227

    Canadian Chemical Transactions Year 2016 | Volume 4 | Issue 2 | Page 226-243

    3t-pentyl-2r,6c-diphenylpiperidin-4-one [7,8], we thought it could be of interest to extend the study to 3t-

    pentyl-2r,6c-diphenylpiperidin-4-one (1a), 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one (1b), 3t-pentyl-

    2r,6c-diphenylpiperidin-4-one oxime (2a), 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one oxime (2b), with

    the aim of characterizing them from the UV-Vis, IR, NMR spectra and to study their preferred

    conformation(s) in gas phase by means of a computational approach. In the present study, DFT/ 6-311G

    (d,p) level theory was used to determine the optimized geometry, vibrational wavenumbers in the ground

    state, non-linear optical properties, HOMO–LUMO energies and Mulliken charges of the molecules.

    Furthermore, NBO analysis of PIPs and PIPOXIs were performed in the same level of theories to

    determine the second order perturbation energy in terms of delocalization energy E (2)

    . In addition, NMR

    chemical shifts were calculated on the optimized geometries using GIAO method at the 6-311+G(2d, p)

    level theory.

    2. EXPERIMENTAL

    2.1. Synthesis of 3t-pentyl-2r,6c-diphenylpiperidin-4-one (1a)

    The compound 1a was prepared according to the procedure given in literature with a little

    modification [9] in Fig. 1. A mixture of ammonium acetate (0.05 mol), benzaldehyde (0.1mol) and 2-

    octanone (0.05 mol) in ethanol were heated to boiling. After cooling, the viscous liquid obtained was

    dissolved in ether (250 ml) and shaken with 10 mL concentrated hydrochloric acid, the precipitated

    hydrochloride of 3t-pentyl-2r,6c-diphenylpiperidin-4-one was removed by filtration and washed first with

    a mixture of ethanol and ether (1:1) and then with ether to remove most of the coloured impurities. The

    base was liberated from an alcoholic solution by adding aqueous ammonia and then diluted with water.

    The products were recrystallized from alcohol.

    2.2. 3t-pentyl-2r,6c-diphenylpiperidin-4-one oxime (2a).

    The compound 2a was prepared according to the procedure given in literature with a little

    modification [9]. 3t-pentyl-2r,6c-diarylpiperidin-4-one (0.05 mol) and sodium acetate trihydrate (0.15

    mol) were dissolved in boiling ethanol and hydroxylamine hydrochloride (0.06 mol) was added. The

    mixture was heated to 40ºC and stirred for 3-4 h and then poured into crushed ice. The separated solid

    was filtered off and recrystallized from ethanol.

    2.3. Synthesis of 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one(1b)

    The compound 1b was prepared according to the procedure given in literature with a little

    modification [9]. Dry ammonium acetate (0.05 mol) was dissolved in 50 mL ethanol and the solution was

    mixed with thiophene-2-carboxaldehyde (0.1mol) and 2-octanone (0.05mol) to give a homogenous

    mixture. Then the mixture was heated to boiling for about 30 minutes. After cooling, the viscous liquid

    was dissolved in ether (300 mL) and shaken with 10 mL concentrated hydrochloric acid and the

    hydrochloride of 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one obtained was separated by filtration

    and washed with a mixture of ethanol and ether (1:1) to remove most of the coloured impurities. The

    product was liberated from an alcoholic solution by adding aqueous ammonia and then diluted with water.

    The crude sample was recrystalized from ethanol. Yield 75%; m.p.: 138-140 (ºC); MF: C18H23NOS2;

    Elemental analysis: Calcd (%): C, 64.82; H, 6.95; N, 4.20; S, 19.23; Found (%):C, 64.91; H, 6.99; N,

    4.31; S, 19.30. Mass (m/z): 334 (M + ), 336, 335, 334.

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    Canadian Chemical Transactions Year 2016 | Volume 4 | Issue 2 | Page 226-243

    Figure 1. Numbering Pattern of PIPs and PIPOXIs.

    2.4. Synthesis of 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one oxime (2b)

    The compound 2b was prepared according to the procedure given in literature with a little

    modification [9]. 3t-pentyl-2r,6c-di(thiophen-2-yl)piperidin-4-one (0.05 mol) and sodium acetate

    trihydrate (0.15 mol) were dissolved in boiling ethanol and hydroxylamine hydrochloride

    (0.06 mol) was added. The mixture was kept warm at 40ºC, stirred for 3-4 h and then poured into crushed

    ice. The separated solid was filtered off and recrystallized from ethanol. Yield 79%; m.p.: 116-118 (ºC);

    MF: C18H24N2OS2; Elemental analysis: Calcd (%): C, 62.03; H, 6.94; N, 8.04; S, 18.40; Found (%): C,

    61.91; H, 6.96; N, 8.00; S, 18.35. Mass (m/z): 348 (M + ), 351, 350, 349, 77.

    2.5. Spectral measurements

    The UV–Visible spectra of the compounds were recorded in SHIMADZU UV-1800 UV–Visible

    Spectrophotometer at room temperature. The FT-IR spectra of the synthesized piperidone and their oxime

    were taken in the range 4000-400 cm -1

    on an AVATAR-330 FT-IR spectrometer (Thermo Nicolet) using

    KBr (pellet form). 1 H NMR spectra were recorded at 400 MHz and

    13 C NMR spectra at 100MHz on a

    BRUKER model using CDCl3 as solvent. Tetramethylsilane (TMS) was used as internal reference for all

    NMR spectra, with chemical shifts reported in δ units (parts per million) relative to the standard.

    2.6. Theoretical background

    All calculations were carried out by density functional theory (DFT) on a personal computer

    using Gaussian 03W program package [10].The calculations were done with the B3LYP level and the

    basis set 6-311G(d,p) [8] was used in the present study to investigate the molecular and vibrational

    frequency of molecules in the ground state in order to support and explain the experimental observations.

    Mulliken, frontier molecular orbital and Non-linear o

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