Synthesis, spectral, crystallographic, and computational investigation of a novel molecular hybrid 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones European Journal of Chemistry 12 (2) (2021) 133-146 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2021 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.12.2.133-146.2073 European Journal of Chemistry View Journal Online View Article Online Synthesis, spectral, crystallographic, and computational investigation of a novel molecular hybrid 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones Kannan Gokula Krishnan 1,2 and Venugopal Thanikachalam 2,* 1 Department of Chemistry, Government Arts and Science College for Women, Karimangalam - 635 111, Tamil Nadu, India gokulakrishnank83@gmail.com (K.G.K.) 2 Department of Chemistry, Annamalai University, Annamalainagar - 608 002, Tamil Nadu, India profvt.chemau@gmail.com (V.T.) * Corresponding author at: Department of Chemistry, Annamalai University, Annamalainagar - 608 002, Tamil Nadu, India. e-mail: profvt.chemau@gmail.com (V. Thanikachalam). 10.5155/eurjchem.12.2.133-146.2073 Received: 21 January 2021 Received in revised form: 28 February 2021 Accepted: 07 March 2021 Published online: 30 June 2021 Printed: 30 June 2021 Synthesis of 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones (1-5) was accomplished and it was characterized experimentally using various analytical techniques. Computational studies have been carried out for all compounds 1-5 using B3LYP method with 6- 311++G(d,p) basis set. The optimized structural features viz. bond lengths, bond angles, and dihedral angles are compared with their single-crystal X-ray diffraction results of compound 1 (Crystal data for C18H13NO4 (M = 307.29 g/mol): Monoclinic, space group P21/c (no. 14), a = 11.399(5) Å, b = 5.876(5) Å, c = 21.859(5) Å, β = 91.060(5)°, V = 1463.9(14) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.100 mm-1, Dcalc = 1.394 g/cm3, 13555 reflections measured (3.58° ≤ 2Θ ≤ 56.98°), 3669 unique (Rint = 0.0235) which were used in all calculations. The final R1 was 0.0444 (>2sigma(I)) and wR2 was 0.1506 (all data)), which are in good conformity with each other. Normal modes of vibrational frequencies of compounds 1-5 acquired from density-functional theory (DFT) method coincided with the experimental ones. The 1H and 13C chemical shifts of compounds 1-5 have been calculated by GIAO method and the results have been compared with the experimental ones. The first-order hyperpolarizability and their related properties of the novel molecules 1-5 are calculated computationally. The other parameters like natural bond orbital, zero-point vibrational energy, EHOMO, ELUMO, heat capacity and entropy have also been discussed. NMR Oxime esters NBO analysis Single crystal XRD Vibrational frequencies Computational chemistry Cite this: Eur. J. Chem. 2021, 12(2), 133-146 Journal website: www.eurjchem.com 1. Introduction Oxygen containing heterocycles are ubiquitous in a broad spectrum of organic molecules and they are essential in synt- hetic organic chemistry and drug discovery [1]. Coumarin and its derivatives have been extensively studied due to their excellent pharmacological activity and its wide occurrence in various species of plants. Particularly, plants belonging to the natural orders of orchids (orchidaceae), legumes (leguminosae), tonkabeans (dipteryxodorata), apiaceae (umbelliferae), labiatae and rutaceae are rich sources of naturally occurring coumarins [2]. Coumarins have been assorted with therapeutic findings which include antimicrobial, anti-cancer, anticoagulant, anti- viral, anti-inflammatory, and antioxidant properties [3-9]. Besides the potential medicinal applications, coumarin has also been used in chemosensors, dye sensitizers, photo triggers, fluorescent labels and probes in biology and medicine [10-13]. Lately, derivatives of coumarin like 3-acyl, 3-benzoyl and 3- carboxamido-2H-chromen-2-ones have a keen to significant role in the treatment of neuropsychiatric disorders [14,15]. Oximes [16] and their derivatives like ethers, esters, and carbonates have been privileged over the past decades because of their wide range of pharmaceutical activities and biological functions. Especially, oxime esters have established a biolo- gically active molecule which includes anti-microbial, anti- convulsant, RBBP9, larvicidal activities, and agrochemical industries [17-21]. Recently, oxime esters have been reported to exhibit DNA-cleaving [22] ability in a process that is triggered by UV light. The structural diversity of organic molecules owing to coumarin moieties reported in the literature stimulated us to proceed with the research on oxime ester moieties and we herein report the synthesis and computational investigation on compounds 1-5. The molecular structural parameters, vibrational frequencies, and nuclear resonance spectra have been computed for the synthesized compounds 1-5 with B3LYP/6-311++G(d,p) level of calculations. Theoretical results like optimized structural features, FT-IR, FT-Raman assign- ment, 1H and 13C chemical shift values are compared with the experimental ones which are in good agreement with each other. HOMO-LUMO energy, Natural Bond Orbital (NBO) analysis, Non-Linear Optical (NLO), and thermodynamic properties were also discussed. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.12.2.133-146.2073 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.12.2.133-146.2073 mailto:gokulakrishnank83@gmail.com mailto:profvt.chemau@gmail.com mailto:profvt.chemau@gmail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.12.2.133-146.2073&domain=pdf&date_stamp=2021-06-30 134 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 O N O 1-5 O N O POCl3, Pyridine O O R R1 = H R2 = p-NO2 R3 = p-Me R4 = o-Cl R5 = p-Cl OH O R OH O O O NH2OH.HCl NaOAc.3H2O EtOH Scheme 1. Synthesis of 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones (1-5). 2. Experimental 2.1. General procedure for the synthesis of 3-(1- ((benzoyloxy)imino)ethyl)-2H-chromen-2-ones (1-5) To a stirred solution of benzoic acid (0.335 g, 2.75 mmol) in dry pyridine (5 mL), POCl3 (0.25 mL, 2.75 mmol) was added drop wise. After 5 min, 3-(1-(hydroxyimino)ethyl)-2H-chro men-2-one (0.5 g, 2.5 mmol) was added to the reaction mixture, stirring was continued for 20 min and the progress of the reaction was monitored by TLC. Upon completion of the reaction, a saturated solution of NaHCO3 was added portion wise to the reaction mixture and the crude product was thrown out as a precipitate and the precipitate was filtered, then recrystallized from ethanol to get the pure 3-(1-((benzoyloxy) imino)ethyl)-2H-chromen-2-one 1 with an excellent yield (0.65 g, 84%). The above general method was adopted for the synthesis of compounds 2-5 (Scheme 1). The melting points of compounds 1-5 were measured in open capillaries and are uncorrected. 3-(1-((Benzoyloxy)imino)ethyl)-2H-chromen-2-one (1): Color: Colorless solid. Yield: 84%. M.p.: 138-140 °C. FT-IR (KBr, ν, cm-1): 2849-3090 (C-H str.), 1739 (C=Olactone str.), 1694 (C=Oester str.), 1622 (C=N str.), 1604 (C=C str.), 701 (N-O str.). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.21 (s, 1H, Ar-H), 8.10 (t, 2H, Ar-H), 7.33-7.64 (m, 7H, Ar-H), 2.56 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 16.09 (CH3), 163.66 (C=Oester), 159.29 (C=Olactone), 154.39 (C=N), 162.74, 143.60, 133.75, 133.70, 133.47, 133.05, 130.61, 130.20, 129.79, 129.66, 129.35, 129.16, 128.92, 128.73, 128.66, 128.51, 125.00, 123.47, 118.55, 116.72 (aromatic carbons). Anal. calcd. for for C18H13NO4: C, 70.35; H, 4.26; N, 4.56. Found: C, 70.32; H, 4.28; N, 4.55%. 3-(1-(((4-Nitrobenzoyl)oxy)imino)ethyl)-2H-chromen-2-one (2): Color: Colorless solid. Yield: 85%. M.p.: 154-157 °C. FT-IR (KBr, ν, cm-1): 2849-3116 (C-H str.), 1746 (C=Olactone str.), 1726 (C=Oester str.), 1623 (C=N str.), 1605 (C=C str.), 714 (N-O str.). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.36 (s, 2H, Ar-H), 8.32 (s, 2H, Ar-H), 8.20 (s, 1H, Ar-H) 7.60 (d, 2H, J = 6.4 Hz, Ar-H), 7.35 (t, 2H, Ar-H), 2.58 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 16.20 (CH3), 163.83 (C=Oester), 159.12 (C=Olactone), 154.44 (C=N), 161.82, 150.90, 143.73, 134.17, 133.30, 130.90, 130.76, 129.17, 125.09, 123.90, 123.06, 118.41, 116.80 (Aromatic carbons). Anal. calcd. for C18H12N2O6: C, 61.37; H, 3.43; N, 7.95. Found: C, 61.33; H 3.42; N 7.89%. 3-(1-(((4-Methylbenzoyl)oxy)imino) ethyl)-2H-chromen-2- one (3): Color: Colorless solid. Yield: 65%. M.p.: 139-140 °C. FT- IR (KBr, ν, cm-1): 2855-3114 (C-H str.), 1753 (C=Olactone str.), 1723 (C=Oester str.), 1627 (C=N str.), 1608 (C=C str.), 741 (N-O str.). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.20 (s, 1H, Ar-H), 8.01 (d, 2H, J = 6.8 Hz, Ar-H), 7.58 (d, 2H, J = 6.8 Hz, Ar-H), 7.27-7.37 (m, 4H, Ar-H), 2.55 (s, 3H, CH3), 2.44 (s, 3H, m-CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 16.03 (CH3), 21.82 (m-CH3), 163.68 (C=Oester), 159.29 (C=Olactone), 154.36 (C=N), 162.46, 144.55, 143.48, 133.00, 129.81, 129.67, 129.43, 129.32, 129.10, 128.58, 125.83, 124.98, 123.55, 118.56, 116.69 (Aromatic carbons). Anal. calcd. for C19H15NO4: C, 71.02; H, 4.71; N, 4.36. Found: C, 71.00; H, 4.73; N, 4.31%. 3-(1-(((2-Chlorobenzoyl)oxy)imino) ethyl)-2H-chromen-2- one (4): Color: Colorless solid. Yield: 78%. M.p.: 142-143 °C. FT- IR (KBr, ν, cm-1): 2847-3090 (C-H str.), 1763 (C=Olactone str.), 1718 (C=Oester str.), 1627 (C=N str.), 1605 (C=C str.), 750 (N-O str.). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.20 (s, 1H, Ar-H), 7.89 (d, 1H, J = 7.2 Hz, Ar-H), 7.29-7.62 (m, 7H, Ar-H), 2.52 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 16.45 (CH3), 163.27 (C=Oester), 159.16 (C=Olactone), 154.35 (C=N), 163.18, 143.62, 133.64, 133.15, 133.11, 131.66, 129.12, 129.00, 126.88, 125.02, 123.27, 118.47, 116.68 (Aromatic carbons). Anal. calcd. for C18H12ClNO4: C, 63.26; H, 3.54; N, 4.10. Found: C 63.23; H 3.52; N 4.08%. 3-(1-(((4-Chlorobenzoyl)oxy)imino) ethyl)-2H-chromen-2- one (5): Color: Colorless solid. Yield: 82%. M.p.: 146-148 °C. FT- IR (KBr, ν, cm-1): 2849-3094 (C-H str.), 1756 (C=Olactone str.), 1720 (C=Oester str.), 1626 (C=N str.), 1607 (C=C str.), 746 (N-O str.). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.19 (s, 1H, Ar-H), 8.06 (d, 2H, J = 7.6 Hz, Ar-H), 7.32-7.63 (m, 6H, Ar-H), 2.55 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 16.07 (CH3), 162.98 (C=Oester), 159.21 (C=Olactone), 154.40 (C=N), 162.80, 143.56, 140.22, 133.11, 131.13, 129.12, 127.10, 125.02, 123.35, 118.50, 116.74 (Aromatic carbons). Anal. calcd. for C18H12ClNO4: C, 63.26; H, 3.54; N, 4.10. Found: C, 63.23; H, 3.56; N, 4.09%. 2.2. Single crystal X-ray crystallography The analyzed crystal 1 has grown by slow evaporation method using ethanol as solvent. The crystal structure of compound 1 belongs to a monoclinic system with P21/c symmetry. Details of the crystal data, data collection and refinement parameters for compound 1 are summarized in Table 1. Selected bond lengths, bond angles, and dihedral angles of compound 1 are given in Table 2. The ORTEP view of compound 1 with atomic labelling is shown in Figure 1, while Figure 2 shows the molecular packing arrangement in the unit cell. Determination of the unit cell parameters and data collection were performed on a Bruker 2008 SMART APEX II diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 293 (2) K with a crystal of size 0.30 x 0.25 x 0.20 mm. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as Supplementary Publication No. of compound 1 is CCDC 1036818. 2.3. Spectral measurements FT-IR spectra of compounds 1-5 were acquired on an AVATAR-300 FT-IR spectrometer using KBr pellet. The spectral assignments are reported in wavenumber (cm-1). FT-Raman spectra were recorded on a Bruker RFS 27: Stand-alone FT- Raman Spectrometer in solid state. The laser source used for the analysis is Nd: YAG 1064 nm. NMR spectra (1H and 13C) were recorded on a Bruker 400 MHz spectrometer. Chemical shift values are reported in parts per million (ppm) from tetramethylsilane (TMS). Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 135 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 1. Crystal data and structural refinement for compound 1. Empirical formula C18H13NO4 Formula weight 307.29 Temperature (K) 293(2) Crystal system Monoclinic Space group P21/c a (Å) 11.399(5) b (Å) 5.876(5) c (Å) 21.859(5) β (°) 91.060(5) Volume (Å3) 1463.9(14) Z 4 ρcalc (g/cm3) 1.394 μ (mm-1) 0.100 F(000) 640.0 Crystal size (mm3) 0.30 × 0.25 × 0.20 Radiation MoKα (λ = 0.71073) 2Θ range for data collection (°) 3.58 to 56.98 Index ranges -15 ≤ h ≤ 12, -7 ≤ k ≤ 7, -29 ≤ l ≤ 27 Reflections collected 13555 Independent reflections 3669 [Rint = 0.0235] Data/restraints/parameters 3669/0/209 Goodness-of-fit on F2 1.022 Final R indexes [I≥2σ (I)] R1 = 0.0444, wR2 = 0.1290 Final R indexes [all data] R1 = 0.0753, wR2 = 0.1506 Largest diff. peak/hole (e Å-3) 0.18/-0.15 Figure 1. ORTEP view of compound 1. Figure 2. Packing diagram of compound 1. 2.4. Computational details Theoretical findings have been attained by B3LYP/6- 311++G(d,p) technique using Gaussian 09W program package [23]. The hybrid function, Becke3 (B3) with Lee-Yang-Parr (LYP) correlation function [24,25], has been employed as a cost- effective approach. The optimized structures have been resolved by minimizing the energy with respect to all coordinates without imposing the molecular symmetry constraints. However, the optimized structural parameters have been used for further calculations like vibration frequency, electronic properties, and isotropic chemical shift. The frequency values computed at these levels contain known systematic errors. To bring the theoretical frequencies are in close proximity to the experimental values, the scaling factor values [26,27] of 0.96, 0.97, and 1.01 have been used for C-H, C- X stretching, bending, wagging, ring puckering and torsion vibrational frequencies, respectively. The chemical shifts have been computed at B3LYP/6-311++G(d,p) level using the Gauge Independent Atomic Orbital (GIAO) method [28].The 1H and 13C isotropic chemical shift values were referenced to the corresponding values of TMS, which was calculated at the same level of theory. 3. Results and discussion 3.1. Synthesis The bio-pertinent 3-(1-((benzoyloxy)imino)ethyl)-2H- chromen-2-ones 1-5 has been synthesized by three-step synthetic protocol as outlined in Scheme 1. 136 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 2. Selected structural parameters for compounds 1-5. Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Bond lengths Calc. (Å) Expt. (Å) a Bond lengths Calc. (Å) Bond lengths Calc. (Å) Bond lengths Calc. (Å) Bond lengths Calc. (Å) C1-C2 1.359 1.350 (19) C1-C2 1.359 C1-C2 1.359 C1-C2 1.359 C1-C2 1.359 C1-C5 1.468 1.463 (2) C1-C5 1.468 C1-C5 1.468 C1-C5 1.468 C1-C5 1.468 C1-C15 1.486 1.488 (2) C1-C15 1.485 C1-C15 1.486 C1-C15 1.486 C1-C15 1.486 C2-C3 1.433 1.427 (2) C2-C3 1.432 C2-C3 1.433 C2-C3 1.432 C2-C3 1.432 C3-C4 1.404 1.385 (2) C3-C4 1.404 C3-C4 1.404 C3-C4 1.404 C3-C4 1.404 C3-C8 1.407 1.405 (19) C3-C8 1.408 C3-C8 1.407 C3-C8 1.407 C3-C8 1.407 C4-C9 1.393 1.384 (2) C4-C9 1.392 C4-C9 1.393 C4-C9 1.393 C4-C9 1.393 C4-O35 1.363 1.374 (16) C4-O34 1.363 C4-O34 1.363 C4-O34 1.363 C4-O34 1.363 C5-O35 1.390 1.375 (19) C5-O34 1.389 C5-O34 1.390 C5-O34 1.391 C5-O34 1.390 C5-O36 1.203 1.200 (2) C5-O35 1.203 C5-O35 1.203 C5-O35 1.203 C5-O35 1.203 C8-C11 1.384 1.368 (2) C8-C11 1.384 C8-C11 1.384 C8-C11 1.384 C8-C11 1.384 C9-C10 1.388 1.378 (2) C9-C10 1.388 C9-C10 1.388 C9-C10 1.388 C9-C10 1.388 C10-C11 1.402 1.389 (2) C10-C11 1.402 C10-C11 1.402 C10-C11 1.402 C10-C11 1.402 C15-C16 1.504 1.494 (2) C15-C16 1.504 C15-C16 1.504 C15-C16 1.504 C15-C16 1.504 C15-N20 1.283 1.276 (2) C15-N20 1.284 C15-N20 1.283 C15-N20 1.283 C15-N20 1.283 N20-O21 1.415 1.428 (17) N20-O21 1.421 N20-O21 1.413 N20-O21 1.420 N20-O21 1.417 O21-C22 1.378 1.355 (2) O21-C22 1.369 O21-C22 1.380 O21-C22 1.365 O21-C22 1.376 C22-O23 1.199 1.193 (18) C22-O23 1.199 C22-O23 1.200 C22-O23 1.199 C22-O23 1.200 C22-C24 1.491 1.479 (2) C22-C24 1.497 C22-C24 1.488 C22-C24 1.499 C22-C24 1.490 C24-C25 1.400 1.388 (2) C24-C25 1.400 C24-C25 1.399 C24-C25 1.402 C24-C25 1.399 C24-C26 1.400 1.386 (2) C24-C26 1.399 C24-C26 1.399 C24-C26 1.402 C24-C26 1.399 C25-C27 1.392 1.384 (2) C25-C27 1.389 C25-C27 1.390 C25-C27 1.393 C25-C27 1.390 C26-C29 1.390 1.379 (2) C26-C29 1.388 C26-C29 1.388 C26-C28 1.388 C26-C29 1.389 C27-C31 1.394 1.374 (3) C27-C31 1.390 C27-C31 1.399 C27-C30 1.390 C27-C31 1.392 C29-C31 1.395 1.370 (2) C29-C31 1.391 C29-C31 1.401 C28-C30 1.393 C29-C31 1.393 Bond angles (°) (°) Bond angles (°) Bond angles (°) Bond angles (°) Bond angles (°) C2-C1-C5 120.1 119.1 (13) C2-C1-C5 120.2 C2-C1-C5 120.1 C2-C1-C5 120.1 C2-C1-C5 120.1 C2-C1-C15 121.3 120.5 (14) C2-C1-C15 121.4 C2-C1-C15 121.3 C2-C1-C15 121.3 C2-C1-C15 121.4 C5-C1-C15 118.4 120.2 (13) C5-C1-C15 118.3 C5-C1-C15 118.4 C5-C1-C15 118.5 C5-C1-C15 118.4 C1-C2-C3 121.6 122.4 (14) C1-C2-C3 121.5 C1-C2-C3 121.6 C1-C2-C3 121.6 C1-C2-C3 121.6 C2-C3-C4 117.5 117.6 (13) C2-C3-C4 117.5 C2-C3-C4 117.5 C2-C3-C4 117.6 C2-C3-C4 117.5 C2-C3-C8 123.8 123.9 (14) C2-C3-C8 123.8 C2-C3-C8 123.8 C2-C3-C8 123.8 C2-C3-C8 123.8 C4-C3-C8 118.5 118.3 (14) C4-C3-C8 118.5 C4-C3-C8 118.5 C4-C3-C8 118.5 C4-C3-C8 118.5 C3-C4-C9 121.4 121.8 (13) C3-C4-C9 121.4 C3-C4-C9 121.4 C3-C4-C9 121.4 C3-C4-C9 121.4 C3-C4-O35 120.8 120.5 (13) C3-C4-O34 120.8 C3-C4-O34 120.8 C3-C4-O34 120.8 C3-C4-O34 120.8 C9-C4-O35 117.7 117.6 (13) C9-C4-O34 117.6 C9-C4-O34 117.7 C9-C4-O34 117.7 C9-C4-O34 117.7 C1-C5-O35 116.2 117.0 (12) C1-C5-O34 116.2 C1-C5-O34 116.2 C1-C5-O34 116.2 C1-C5-O34 116.2 C1-C5-O36 126.3 127.1 (15) C1-C5-O35 126.2 C1-C5-O35 126.3 C1-C5-O35 126.3 C1-C5-O35 126.3 O35-C5-O36 117.4 115.8 (14) O34-C5-O35 117.5 O34-C5-O35 117.3 O34-C5-O35 117.4 O34-C5-O35 117.4 C3-C8-C11 120.4 120.2 (15) C3-C8-C11 120.3 C3-C8-C11 120.4 C3-C8-C11 120.4 C3-C8-C11 120.4 C4-C9-C10 118.8 118.4 (15) C4-C9-C10 118.7 C4-C9-C10 118.8 C4-C9-C10 118.8 C4-C9-C10 118.8 C9-C10-C11 120.8 120.9 (15) C9-C10-C11 120.8 C9-C10-C11 120.8 C9-C10-C11 120.8 C9-C10-C11 120.8 C8-C11-C10 119.8 120.1 (14) C8-C11-C10 119.8 C8-C11-C10 119.8 C8-C11-C10 119.8 C8-C11-C10 119.8 C1-C15-C16 121.1 122.5 (14) C1-C15-C16 121.1 C1-C15-C16 121.1 C1-C15-C16 121.2 C1-C15-C16 121.1 C1-C15-N20 113.3 112.4 (13) C1-C15-N20 113.2 C1-C15-N20 113.3 C1-C15-N20 113.1 C1-C15-N20 113.3 C16-C15-N20 125.4 125.0 (15) C16-C15-N20 125.5 C16-C15-N20 125.4 C16-C15-N20 125.5 C16-C15-N20 125.5 C15-N20-O21 110.8 110.2 (12) C15-N20-O21 110.6 C15-N20-O21 110.9 C15-N20-O21 110.6 C15-N20-O21 110.8 N20-O21-C22 113.2 112.5 (11) N20-O21-C22 113.1 N20-O21-C22 113.2 N20-O21-C22 113.3 N20-O21-C22 113.1 O21-C22-O23 124.1 123.9 (15) O21-C22-O23 124.9 O21-C22-O23 123.9 O21-C22-O23 125.0 O21-C22-O23 124.3 O21-C22-C24 110.5 110.7 (13) O21-C22-C24 110.4 O21-C22-C24 110.5 O21-C22-C24 110.7 O21-C22-C24 110.5 O23-C22-C24 125.3 125.2 (16) O23-C22-C24 124.6 O23-C22-C24 125.4 O23-C22-C24 124.0 O23-C22-C24 125.1 C22-C24-C25 122.8 122.9 (15) C22-C24-C25 122.7 C22-C24-C25 123.1 C22-C24-C25 126.0 C22-C24-C25 123.0 C22-C24-C26 117.4 117.7 (14) C22-C24-C26 117.2 C22-C24-C26 117.7 C22-C24-C26 115.6 C22-C24-C26 117.5 C25-C24-C26 119.6 119.3 (15) C25-C24-C26 119.9 C25-C24-C26 119.1 C25-C24-C26 118.2 C25-C24-C26 119.4 C24-C25-C27 119.9 119.9 (17) C24-C25-C27 120.1 C24-C25-C27 120.1 C24-C25-C27 120.6 C24-C25-C27 120.4 C24-C26-C29 120.1 120.1 (15) C24-C26-C29 120.3 C24-C26-C29 120.3 C24-C26-C28 121.3 C24-C26-C29 120.6 C25-C27-C31 120.1 120.1 (16) C25-C27-C31 118.6 C25-C27-C31 121.2 C25-C27-C30 120.0 C25-C27-C31 119.1 C26-C29-C31 120.0 120.2 (17) C26-C29-C31 118.5 C26-C29-C31 121.0 C26-C28-C30 119.5 C26-C29-C31 119.0 C27-C31-C29 120.0 120.2 (17) C27-C31-C29 122.3 C27-C31-C29 118.1 C27-C30-C28 120.1 C27-C31-C29 121.3 C4-O35-C5 123.4 123.1 (12) C4-O34-C5 123.4 C4-O34-C5 123.4 C4-O34-C5 123.4 C4-O34-C5 123.4 The key component, 3-acetyl-2H-chromen-2-one has synthesized by Knoevenagel condensation of salicylaldehyde with ethyl acetoacetate in 1:1 molar ratio followed by oximation using hydroxylamine hydrochloride in the presence of sodium acetate trihydrate in ethanol gave 3-(1-(hydroxyimino)ethyl)- 2H-chromen-2-one in good yields. In the eventual step, bio- pertinent 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones 1-5 have been synthesized from 3-(1-(hydroxyimino)ethyl)- 2H-chromen-2-one with benzoic acid using POCl3 [29] and pyridine as solvent as well as base afforded the corresponding oxime esters 1-5 in good yields. 3.2. Molecular geometry From the single crystal XRD measurements of compound 1, both the pyrone and benzene rings in the coumarin motif are essentially planar, which is evidenced by the dihedral angle value between their carbons C2-C3-C4-C9 [178.9(13)°]. The imino (C=N) group of oxime ester adopts an anti-orientation relative to the C=C double bond [C1-C15-N20-O21 178.0 (11)°]. Thus, the molecule is about C-C=N bond which is found to exist in E-isomer with respect to the olefinic C=C bond. In addition, the bond angles of the imino group versus the coumarin moiety and methyl group are 112.4(13)°, 125.0(15)° [C-C=N], respect- tively. These values are emblematic of the angle permitted by the rotation present at position 3. Presence of the imino group at position 3 provokes a non-coplanarity of the oxime ester moiety relative to the parent coumarin. The optimized structural features (bond lengths, bond angle, and dihedral angles) for thermodynamically preferred geometry of compounds 1-5 were computed at B3LYP/6- 311++G(d,p) level. Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 137 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 1 2 3 4 5 Figure 3. Optimized geometry and atom numbering of compounds 1-5. Theoretically, resulted structural parameters were compared with the single crystal XRD values of compound 1. The optimized structures for compounds 1-5 are shown in Figure 3. The mean C-H bond lengths of compounds 1-5 are 1.08 Å, in good agreement with the experimental value of C-H bond [30, 31]. Bond lengths connecting to the ring carbons are found to be around 1.38-1.40 Å, which is in-line with the expected range of title molecule, 1.368-1.407 Å. The computed bond angles of sp2hybrids of ring carbons are around 120°. Double bond length of carbon-nitrogen, carbon-oxygen and single bond length of carbon-oxygen, nitrogen-oxygen are about 1.28, 1.20, 1.37, and 1.41 Å, respectively, which are found to coincide with their experimental results [32]. The side chain, 3-acetyl part of compounds 1-5 are bonded to the C1 atom of the coumarin ring. The geometry of the coumarin ring is planar as indicated by C2-C3-C4-C9 (-179.2°) and C8-C3-C4-O35 (-179.9°) which are matched with the experimental values and are listed in Table 2. The dihedral angles C2-C1-C15-C16 (-141.9°, -141.7°, -142.1°) and C2-C1- C15-N20 (36.1°, 36.4°, 35.9°, 36.0) indicate that the 3-acetyl part deviated from the coumarin ring i.e. the 3-acetyl part lies in other plane. 3.3. Vibrational analysis The combined experimental and theoretically simulated Infra-red and Raman spectra of the compounds 1 under investigation are shown in Figure 4. The experimental and theoretically computed frequencies along with their relative intensities, probable assignments, and potential energy distribution (PED) of compound 1 are summarized in Table 3. The hypothetically computed frequencies of the studied compounds 1-5 are in accord with the experimental ones. 3.3.1. C=O and C-O vibrations Compounds possessing carbonyl groups give a strong absorption in the region of 1650-1750 cm-1 [33-36]. In compounds 1-5, the distinctive FT-IR bands emerged at 1694- 1726 and 1739-1763 cm-1 which confirmed the presence of carbonyl groups, while in FT-Raman absorption bands have been appeared at 1713-1724 and 1739-1759 cm-1. The computed carbonyl (C=O) stretching vibrations of ester and lactone carbonyl are at 1734-1759 and 1731-1735 cm-1 which correlated well with the experimental ones. The variations of stretching frequency of the carbonyl group are due to the presence of different substitutions on the phenyl ring in the compounds. The stretching frequency of C-O appeared in the region of 1150-1280 cm-1 [34,35]. In the present study, the bands appeared at 1215-1268 and 1317-1348 cm-1 in FT-IR and at 1210-1268 and 1320-1335 cm-1 in FT-Raman are due to the C- O stretching vibration of the synthesized compounds 1-5. The computed FT-IR and FT-Raman spectral values (1197-1286 and 1313-1336 cm-1) are coincided well with the experimental results. 138 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 3. Experimental and calculated vibrational (FT-IR and Raman) spectral values of compound 1 with their proposed vibrational assignments. Mode no Exp. frequency (cm-1) Calc. frequency (cm-1) Vibrational assignments with PED ≥ 10% * FT-IR FT-Raman Unscaled Scaled IIR IRaman 1 10 10 5.26 3.83 γC3C9O35C4(12) 2 28 28 8.44 5.60 γC15C2C5C1(12); τC15C1C5O35(20) 3 33 33 2.79 6.59 γC22C24C26C25(12) 4 49 49 3.22 13.35 γC16C1N20C15(12) 5 71 72 3.11 7.99 γO23C24O21C22(12) 6 90 91 5.16 3.76 γO36C1O35C5(12); τC4O35C5O36(20) 7 109 110 3.82 3.22 τC1C15N20O21(20) 8 111 112 3.17 5.11 τC24C22O21N21(20) 9 159 161 3.27 3.84 τC1C4C5O35(20) 10 170 172 3.28 5.17 τC15N20O21C22(20) 11 187 189 3.85 6.32 τC26C24C22O21(20) 12 212 214 2.10 3.17 γC11C8C9C10(12) 13 236 238 8.23 5.43 τC27C25C31C29(20) 14 262 265 9.79 7.04 τC26C29C27C31(20) 15 309 312 7.11 2.53 τC24C26C31C29(18) 16 322 325 1.94 3.30 γC9C10O35C4(12); τC9C10C4O35(20) 17 327 330 7.77 8.39 γC10C4C11C9(26) 18 371 375 7.79 3.66 γC8C3C10C11(24) 19 393 386 390 4.07 5.77 τC1C5C2C3(22) 20 417 411 415 2.28 2.91 τC2C1C15N20(25) 21 432 421 425 8.82 7.50 τH34C31C29C26(28) 22 456 450 455 460 6.48 17.9 τH19C16C15C1(18); γC16H18C15H19(12) 23 478 477 466 471 8.62 5.30 τH33C29C31C29(32) 24 480 485 2.45 6.13 τH32C27C31C29(30) 25 496 494 499 8.87 4.92 τH30C26C29C31(38) 26 539 536 548 553 3.23 4.44 τH28C25C27C31(15); γC25C24C27H28(18) 27 556 563 565 571 5.91 2.21 τH18C16C15C1(18); γC16H17C15H18(15) 28 589 586 585 591 9.93 9.91 τH17C16C15C1(20); γC16H18H19H17(10) 29 616 609 608 614 14.2 4.98 τH14C11C10C9(44) 30 635 634 631 637 6.86 10.66 τH13C10C11C8(16); τH13C10C9C4(20) 31 644 650 13.93 5.76 τH12C9C10C11(20) 32 670 674 669 676 33.65 8.03 τH6C8C11C10(18); γH6C11C3C8(20) 33 683 673 680 6.61 8.14 τH7C2C1C5(24) 34 701 699 701 708 17.21 2.60 βC15N20O21(22); γC8C3O35C4(15) 35 718 725 33.65 5.28 βC16C15N20(25); βC1C15C16(10) 36 739 737 746 753 6.95 8.61 βC24C22O21(38) 37 752 760 4.61 26.83 βC4O35C5(42) 38 772 779 770 778 38.03 2.62 βC5C1C15(28); βC2C1C15(14) 39 779 787 17.70 9.89 βC22O21N20(40) 40 800 791 799 9.25 7.41 βC22C24C26(35) 41 822 817 812 820 11.79 6.02 βC8C11C10(33) 42 854 848 856 11.86 12.37 βC25C27C31(38) 43 868 871 858 867 6.26 5.03 βC27C31C29(25) 44 875 884 6.78 1.81 βC26C29C31(26) 45 922 915 931 940 42.01 16.50 βC4C9C10(30) 46 944 939 948 53.33 10.84 βC9C10C11(26) 47 952 962 10.44 5.88 βC3C8C11(28) 48 968 956 966 27.01 6.68 βC2C1C5(38) 49 976 986 20.38 6.88 βC1C15N20(32) 50 991 999 986 996 53.22 16.03 βO35C5O36(15); βC1C5O36(25) 51 993 1003 4.08 0.61 βO21C22O23(18); βC24C22O23(10) 52 1000 1010 2.71 1.90 βH34C31C29(22); βH34C31C27(12) 53 1010 1020 0.64 1.12 βH18C16H19(19); βH17C16H19(21) 54 1024 1024 1018 1028 2.50 28.90 βH33C29C31(20); βH33C29C26(20) 55 1039 1049 28.19 30.38 βH32C27C31(22); βH32C27C25(18) 56 1055 1051 1046 1056 16.97 19.56 βH30C26C29(25); βH30C26C24(12) 57 1051 1062 10.05 17.60 βH28C25C27(28); βH28C25C24(15) 58 1078 1074 1061 1072 5.89 10.09 βH17C16H18(26); βH18C16C15(10) 59 1100 1073 1084 55.08 12.30 βH17C16H19(32); βH17C16C15(14) 60 1125 1129 1110 1121 9.19 9.59 βH14C11C8(25); βH14C11C10(12) 61 1132 1143 30.79 18.54 βH13C10C11(28); βH13C10C9(15) 62 1146 1157 14.16 6.70 βH12C9C10(32); βH12C9C4(10) 63 1183 1195 14.04 11.14 βH6C8C11(30); βH6C8C3(22) 64 1184 1196 3.26 9.19 βH7C2C1(38); βH7C2C3(10) 65 1159 1160 1205 1169 22.06 6.89 νN20O21(35); βC4C3C8(18) 66 1176 1181 1238 1188 64.96 22.37 νC15C16(42) 67 1247 1197 35.14 46.05 νC22C24(44) 68 1215 1215 1271 1233 49.81 34.72 νC5O35(40) 69 1238 1284 1233 38.78 3.84 νC1C15(48) 70 1249 1263 1321 1281 22.69 12.49 νC22O21(52) 71 1334 1281 6.59 2.32 νC1C5(41); βC1C5O35(25) 72 1317 1354 1313 6.14 7.15 νC4O35(42); βC9C4O35(28) 73 1365 1310 5.73 47.22 νC2C3(44); βC1C2C3(26) 74 1320 1330 1389 1333 10.25 14.88 νC3C8(40); βC2C3C8(35) 75 1373 1362 1405 1349 20.75 11.84 νC24C25(45); βC25C24C26(30) 76 1474 1415 13.09 12.00 νC24C26(50); βC24C26C29(28) 77 1477 1418 15.88 5.37 νC10C11(66) 78 1482 1423 18.55 21.48 νC3C4(58) 79 1485 1426 17.21 25.57 νC27C31(60) Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 139 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 3. Continued. Mode no Exp. frequency (cm-1) Calc. frequency (cm-1) Vibrational assignments with PED ≥ 10% * FT-IR FT-Raman Unscaled Scaled IIR IRaman 80 1450 1446 1515 1454 11.46 30.89 νC29C31(62) 81 1488 1490 1522 1461 5.48 5.32 νC27C27(55); βC24C25C27(30) 82 1599 1535 35.29 85.48 νC26C29(66) 83 1556 1555 1620 1555 8.21 11.64 νC4C9(68) 84 1640 1574 16.74 38.17 νC9C10(75) 85 1582 1646 1580 36.33 74.25 νC8C11(72) 86 1604 1601 1653 1587 40.00 100.00 νC1C2(78) 87 1622 1674 1624 13.38 62.13 νC15N20(70) 88 1694 1716 1786 1732 100.00 32.58 νC5O36(75) 89 1739 1745 1791 1737 66.44 50.51 νC22O23(80) 90 2849 2919 3036 2915 13.70 59.36 νC31H34(82) 91 2925 2984 3105 2981 10.91 36.24 νC16H19(80) 92 3009 2997 3141 3015 8.26 37.60 νC29H33(88) 93 3039 3037 3166 3039 1.92 30.25 νC27H32(85) 94 3174 3047 1.04 23.87 νC26H30(89) 95 3178 3051 11.89 45.42 νC25H28(91) 96 3182 3055 8.66 42.28 νC16H18(94) 97 3064 3064 3188 3060 16.99 51.75 νC16H17(90) 98 3196 3068 12.35 48.73 νC11H14(92) 99 3198 3070 4.97 33.88 νC10H13(96) 100 3199 3071 11.36 49.90 νC9H12(95) 101 3226 3205 3077 7.90 66.24 νC8H6(100) 102 3090 3245 3214 3085 7.37 42.00 νC2H7(98) * ν - stretching, β - inplane bending, γ - out of plane bending, τ - torsional vibrations. Figure 4. (a) FT-IR spectrum of compound 1, (b) Simulated FT-IR spectrum of compound 1, (c) FT-Raman spectrum of compound 1, (d) Simulated FT-Raman spectrum of compound 1. 3.3.2. C=N and N-O vibrations Oxime esters containing C=N and N-O bonds show characteristic bands in the region 1620-1690 and 945 cm-1 [37]. In the present case, the peaks appeared in the region of 1622- 1627 and 1134-1165 cm-1 in FT-IR (1606-1687 and 1133-1160 cm-1 in FT-Raman) are assigned to C=N and N-O stretching vibrations. The calculated wave numbers of C=N and N-O stretching vibrations (1622-1631 and 1141-1169 cm-1) coincided with their experimental values. 3.3.3. C=C and C-C vibration The aromatic carbon-carbon stretching frequencies (C=C and C-C) generally arise in the region from 1480 to 1630 cm-1 [38-40]. In our present study, the frequencies occur in FT-IR at 1249-1608 cm-1 and in FT-Raman 1255-1612 cm-1 are owing to the carbon-carbon stretching modes. The theoretically calculated frequencies at 1268-1589 cm-1 by DFT method are well coincided with the experimental values. The C-C-C in-plane and out-of-plane bending modes of compound 1 is presented in Table 3. 3.3.4. C-H vibration The aromatic and heteroaromatic C-H stretching bands are typically occurring below 3100 cm-1 [41,42]. In accordance with this, the absorption bands at 3031-3116 cm-1 in FT-IR spectrum and 3037-3245 cm-1 in FT-Raman spectrum are assigned to the C-H stretching frequency of the studied molecules. The calculated C-H stretching frequencies (3036-3099 cm-1) agreed well with the observed frequencies. 140 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 4. Mulliken atomic charges of compounds 1-5. 1 2 3 4 5 Atom Charge Atom Charge Atom Charge Atom Charge Atom Charge 1C 0.3930 1C 0.3799 1C 0.3503 1C 0.3973 1C 0.3836 2C 0.1149 2C 0.1243 2C 0.1388 2C 0.2270 2C 0.1197 3C 1.5905 3C 1.5959 3C 1.5858 3C 1.6767 3C 1.5904 4C -1.9272 4C -1.9162 4C -1.9292 4C -1.9667 4C -1.9095 5C 0.0043 5C 0.0069 5C 0.0102 5C -0.0991 5C 0.0111 6H 0.1532 6H 0.1534 6H 0.1531 6H 0.1529 6H 0.1531 7H 0.2430 7H 0.2425 7H 0.2445 7H 0.2335 7H 0.2446 8C 0.1599 8C 0.1538 8C 0.1671 8C 0.1874 8C 0.1486 9C -0.3738 9C -0.3847 9C -0.3718 9C -0.3588 9C -0.3888 10C -0.3419 10C -0.3418 10C -0.3446 10C -0.3418 10C -0.3425 11C -0.1521 11C -0.1483 11C -0.1499 11C -0.1542 11C -0.1476 12H 0.2059 12H 0.2076 12H 0.2056 12H 0.2067 12H 0.2062 13H 0.1768 13H 0.1791 13H 0.1764 13H 0.1770 13H 0.1776 14H 0.1745 14H 0.1765 14H 0.1743 14H 0.1749 14H 0.1751 15C 0.2115 15C 0.2204 15C 0.2106 15C 0.0917 15C 0.2123 16C -0.8236 16C -0.8257 16C -0.8168 16C -0.8207 16C -0.8192 17H 0.1881 17H 0.1918 17H 0.1878 17H 0.1856 17H 0.1896 18H 0.1828 18H 0.1819 18H 0.1831 18H 0.1827 18H 0.1819 19H 0.2209 19H 0.2239 19H 0.2204 19H 0.2192 19H 0.2221 20N -0.2842 20N -0.2858 20N -0.2870 20N -0.2717 20N -0.2847 21O 0.2946 21O 0.2984 21O 0.2916 21O 0.3630 21O 0.2858 22C -0.4337 22C -0.2601 22C -0.3636 22C -1.0307 22C -0.4966 23O -0.1855 23O -0.1737 23O -0.1861 23O -0.1618 23O -0.1854 24C 0.9850 24C 1.1426 24C 1.1591 24C 0.3054 24C 0.9388 25C -0.2122 25C -0.2362 25C -0.5008 25C 0.4436 25C -0.4375 26C -0.0464 26C -0.1368 26C -0.1905 26C -0.0102 26C -0.1841 27C -0.3760 27C -0.5543 27C -0.6363 27C -0.3232 27C -0.6539 28H 0.1515 28H 0.1813 28H 0.1278 28H -0.1987 28H 0.1490 29C -0.4879 29C -0.4170 29C -0.5536 29C 0.1979 29C -0.6756 30H 0.2006 30H 0.2192 30H 0.1904 30C -0.4072 30H 0.2059 31C -0.1719 31C -0.1581 31C 0.6036 31H 0.2065 31C 0.3794 32H 0.1843 32H 0.2545 32H 0.1763 32H 0.1776 32H 0.2106 33H 0.1735 33H 0.2515 33H 0.1634 33H 0.1636 33H 0.1988 34H 0.1604 34O -0.0914 34O -0.0949 34O -0.0946 34O -0.0936 35O -0.0941 35O -0.2573 35O -0.2587 35O -0.2551 35O -0.2584 36O -0.2590 36N -0.2247 36C -0.5026 36Cl 0.5241 36Cl 0.4933 37O 0.0169 37H 0.1465 38O 0.0094 38H 0.1733 39H 0.1462 The weak-medium-strong peaks seen at 911-1250 and 387- 553 cm-1 in FT-IR spectra and 909-1236 and 414-536 cm-1 in FT-Raman spectra are due to the effect of C-H in-plane and out- of-plane bending vibrations, respectively [43]. The in-plane and out-of-plane bending vibrations of the C-H bonds have also been identified for the synthesized compounds 1-5 and they agreed with the calculated frequencies as shown in Table 3. 3.3.5. Methyl group vibration The C-H stretching in alkyl groups are clearly obtained at lower frequencies than those of aromatic ring vibrations, i.e., 2970-2840 cm-1 [44-46]. The weak and medium bands for CH3 stretching frequencies are occurred in FT-IR at 2786-3021 cm- 1 and in FT-Raman at 2866-3013 cm-1, whereas the calculated stretching frequencies are 2902-3016 cm-1. The deformation vibrations of CH3 at 1471-1487, 1019- 1089, and 556-680 cm-1 in FT-IR and in FT-Raman at 1488- 1491, 1074-1089 and 563-678 cm-1 are assigned to the mixture deformation modes with C-H and skeleton vibrations. All characteristic assignments obtained from experimental and calculated ones are well synchronized with literature values [47]. 3.3.6. Nitro group vibration Typically, the nitro group stretching frequencies are exhibited as the same as in the C-C stretching regions. The deformation vibrations of NO2 group (rocking, wagging, and twisting) contribute to several normal modes in the low frequency region [48]. In compound 2, the very strong bands observed in FT-IR at 1370 cm-1 and in FT-Raman at 1351 cm-1 are assigned to stretching vibrations of the nitro group and agree well with the observed band at 1331 cm-1. 3.3.7. C-Cl vibrations The vibration frequencies belonging to CX groups (X = Cl, Br, and I) usually occurred in the frequency range of 850-500 cm-1 with more than one halogen atom exhibiting very strong bands due to asymmetric and symmetric stretching modes [43]. In the FT-IR spectra of compounds 4 and 5 the absorption zones at 689 and 694 cm-1 whereas in FT-Raman at 692 and 710 cm-1 are assigned to C-Cl stretching vibrations of the molecule. The calculated wave numbers of C-Cl stretching bands arising at 708 and 703 cm-1 by B3LYP/6-311++G (d,p) coincided very well with the experimental value. The band at 474 cm-1 for compound 4 and at 525 cm-1 for compound 5 in FT-IR are assigned to the C-Cl torsion mode of vibration. 3.4. Mulliken population analysis The atomic charges of an individual atom are determined via Mulliken population analysis. Mulliken electron populations of compounds 1-5 have been acquired from the optimized structural calculation and the values are collected in Table 4. The charge distributions over the atoms suggest the formation of donor and acceptor pairs involving the charge transfer in the molecule [49]. In compounds 1-5, the magnitude of carbon (3C) atom has gained higher positive charge and becomes more acidic, while carbon (4C) has high negative charge than the other atoms due to the fusion of benzene ring and pyrone ring through a more electronegative oxygen atom. Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 141 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 5. Calculated HOMO-LUMO energies of compounds 1-5. Parameters 1 2 3 4 5 EHOMO -8.4261 -8.4416 -8.4168 -8.4241 -8.4114 ELUMO -5.5596 -5.5830 -5.5542 -5.5501 -5.5498 ∆E 2.8665 2.8586 2.8626 2.8740 2.8616 EHOMO -1 -9.0585 -9.0655 -9.0500 -8.9162 -8.9227 ELUMO +1 -5.0589 -5.3218 -4.9756 -4.8570 -4.8899 ∆E1 3.9996 3.7437 4.0744 4.0592 4.0328 All hydrogen and carbon atoms in the coumarin and ester fragments are carrying positive and negative charges, respect- tively. Besides, 3C and 24C are holding positive charges. The results suggest that the electron delocalization takes place in the entire molecule [50]. 3.5. NBO analysis Natural bond orbital (NBO) analysis grants a new approach to studying natural charges, bond types, bond order, charge transfer, and donor-acceptor interactions in a molecule [51-53]. The hyper-conjugative interaction energy of a molecule was deduced from the second order perturbation approach (SOPT). 𝐸𝐸(2) = ∆𝐸𝐸𝑖𝑖𝑖𝑖 = 𝑞𝑞𝑖𝑖 𝐹𝐹(𝑖𝑖,𝑖𝑖)2 𝜀𝜀𝑗𝑗−𝜀𝜀𝑖𝑖 (1) where qi is the donor orbital occupancy, εi and εj are diagonal elements, and F(i,j) is the off-diagonal NBO Fock matrix element. The SOPT analysis of Fock matrix of compounds 1-5 has been carried out with B3LYP/6-311++G(d,p) method. For convenience, compound 1 has been selected for discussion. The significant interactions between bond and antibonding orbitals with lone pair electrons and their corresponding E(2) of the molecule were observed. An effective interaction has been observed between the lone pair of electrons on oxygen (O23 and O35) and the antibonding orbitals of coumarin and benzoyl parts. These interactions are formed by the orbital overlap between bonding and antibonding orbitals, which result in intramolecular charge transfer (ICT) causing stabilization of the molecule. The stabilization energy E(2) of n(O21) → π*(C22- O23), n(O23) → σ*(O21-C22), n(O35) → π*(C3-C4), n(O35) → π*(C5-O36), n(O36) → π*(C5-O35), π*(C3-C4) → π*(C1-C2), π*(C3-C4) → π*(C8-C11), π*(C5-O36) → π*(C1-C2),) π*(C27- C31) → π*(C29-H33) are 37.17, 37.47, 28.97, 35.5, 35.64, 184.22, 259.02, 84.35 and 28.82 kcal/mol. High E(2) values indicate that the strong interaction observed between electron donor and acceptors which results in extended conjugation occurs in the molecular system. Moreover, the higher values of E(2) are chemically significant and have been used as to measure the intermolecular hydrogen bonding (C-H---O) interaction between the lone pair of oxygen and the antibonding orbitals. The electron density of six conjugated π bonds (~1.6) and π* bond (~0.3) in the benzoyl group and benzene ring of coumarin have clearly demonstrated strong delocalization. The stabiliza- tion energies of π→π* electrons in benzoyl group and in benzene ring are 17.05, 18.73, 15.98, 17.59 21.13, 22.38, 16.92, 20.18, 20.55, 19.26, 22.53 and 18.12 kcal/mol. The stabilization energies of π→π* electrons in compounds 2-5 are higher than compound 1 and the antibonding interactions between the lone pair of electrons are higher, which reveal that compounds 2-5 form intramolecular charge transfer which leads to a greater extent of conjugation in the molecule. 3.6. HOMO-LUMO analysis From the optimized structural calculation, HOMO, LUMO and band gap energies of compounds 1-5 were determined and 3D plots of compounds 1-5 are shown in Figure 5. The color codes, red and green designate the positive and negative phases of the molecules. The energy gap between HOMO and LUMO of compounds 1-5 decreases in the order: 2 > 5 > 3 > 1 > 4 and the values are tabulated in Table 5. From Figure 5, the HOMO of molecular charges is spread over the coumarin ring and imino group, while the LUMO implies a slight electron density transfer from the coumarin ring to the oxime ester part, which increases the molecular polarity of compounds 1-5. Among compounds 1-5, compound 2 has the minimum energy gap which results in the eventual charge transfer taking place within the molecule due to the presence of an electronegative group in the molecule. Furthermore, the HOMO-LUMO energy gap of compounds 1-5 are compared with their corresponding coumarin derivatives [34,35,54-56] like 3-acetyl-2H-chromen-2-one (4.176 eV), 3-(1- (((methoxycarbonyl)oxy) imino)ethyl)-2H-chromen-2-one (4.244 eV), (Z)-N-Cyclohexyl-2-(2-((2-oxo-2H-chromen-3-yl)- methoxy)benzylidene)hydrazinecarbothioamide (3.053 eV), (Z)-N-(2, 4-Dimethylphenyl)-2-(2-((2-oxo-2H-chromen-3- yl)methoxy)benzylidene)hydrazinecarbo-thioamide (3.118 eV) 7-hydroxy-2H-chromen-2-one (4.420 eV) and 3-cyano-4- methyl-2H-chromen-2-one (4.292 eV), the compounds 1-5 are found to have lesser energy gap than the above mentioned compounds due to the introduction of oxime ester into the 3- acetyl part. 3.7. NMR spectral analysis The 1H and 13C chemical shifts of compounds 1-5 have been calculated by B3LYP/6-311++G(d,p) method. A sharp singlet with three protons integrals resonated in the shielded region at ∼2.5 ppm corresponding to the presence of methyl protons (17H, 18H, and 19H) of compounds 1-5 and the values are matched well with the computed chemical shifts. The signal of olefinic proton 7H of compounds 1-5 appeared to be shielded by 0.25 ppm with respect to the parent 3-acetyl-2H-chromen- 2-one [34]. The same 7H proton signal was deshielded by 0.13 ppm with respect to 3-(1-(((methoxycarbonyl)oxy)-imino) ethyl)-2H-chromen-2-one [35]. This suggests a weakening/ strengthening of the π-π conjugation between the lactone carbonyl and the imino group. The aromatic protons of coumarin and o-benzoyl groups are seen in the downfield region from 7.29 to 8.36 ppm. The aromatic carbon signals are generally arising in the range from 100 to 160 ppm in organic molecules [57]. In the present study, the aromatic carbons fall in the down field region 116-154 ppm, which are in accord with the computed ones. The signals appeared in the up field from 16.03-16.45 ppm corresponding to the methyl carbon of compounds 1-5, which coincide well with the calculated results (19.11-22.3 ppm). Carbonyl carbons of o-benzoyl lactone and imino carbon [35] are appeared in the far downfield region at 161-154 ppm. In the present case, the characteristic signals appeared in the range of 163-159 ppm are assigned to o-benzoyl lactone and imino carbons. 3.8. Molecular electrostatic potential The molecular electrostatic potential (MEP) mapping is a powerful tool that provides insights into reactive sites and physicochemical relationships as well as hydrogen-bonding interactions of a molecule [58]. 142 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 HOMO LUMO 1 2 3 4 5 HOMO LUMO Figure 5. HOMO-LUMO plots of compounds 1-5. To predict the reactive sites of the synthesized molecules 1- 5 MEPs are investigated. Figure 6 shows the electrostatic potential of compounds 1-5, computed at 0.002 a.u. isosurface. The electrostatic potential increases in the order: red 5 > 4 > 1 > 3 and the trend of average polarizability are 2 > 5 > 4 > 3 > 1, respectively. Besides, the average polarizability values of the synthesized compounds 1-5 are compared with p- nitroaniline. The results suggest that the studied compounds hold higher values than p-nitroaniline [60]. The computed hyperpolarizability value (β) of compounds 1-5 decreased in the order: 1 > 3 > 4 > 5 > 2, respectively. Besides, the total first hyperpolarizability of compounds 2 (5.7478×10-30 esu) and 5 (2.073×10-30 esu) are superior to other compounds. Further- more, the first hyperpolarizability values of compounds 1-5 are compared with urea (0.372×10-30 esu). The hyperpolarizability values (β) of compounds 2 and 5 are almost fifteen and six times superior to urea where as for other compounds, they are 1.6 and 2.2 times greater than urea [61]. In addition, the dipole moments of compounds 1-5 are higher than that of urea (1.373 Debye). 144 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 Table 6. Calculated thermodynamic parameters of compounds 1-5. Parameters 1 2 3 4 5 SCF energy (a.u.) -1043.314 -1254.193 -1088.962 -1509.251 -1509.254 Total energy (kcal/mol) 181.340 184.306 199.558 175.997 176.020 Zero point energy (kcal/mol) 169.379 170.678 186.408 163.228 163.264 Rotational constants (GHz) x y z 0.586 0.126 0.110 0.554 0.076 0.072 0.572 0.105 0.094 0.474 0.114 0.105 0.574 0.084 0.078 Entropy (cal/mol.K) 148.358 162.726 158.471 154.337 155.490 Heat capacity (cal/mol.K) 73.451 82.204 79.544 77.374 77.364 Figure 7. Correlation of the effect of temperature on heat capacity (Cp), entropy (S), and enthalpy change (ΔH0→T) of compound 1. From the above results, we conclude that the molecular polarizability and hyperpolarizability of the studied compounds 1-5 in all coordinates are active and so it can be used to prepare NLO crystals which may produce second order harmonic waves and among these the nitro derivative is the best NLO candidate for future study. 3.10. Thermodynamic properties The temperature dependence of thermodynamic properties viz. the heat capacity, entropy, enthalpy change, and zero-point vibrational energy of compounds 1-5 have been calculated by B3LYP/6-311++G(d,p) technique and the values are summa- rized in Table 6. To bring the thermodynamic properties in accurately, the scale factors have been used [62,63]. The correlations of heat capacity, entropy, and enthalpy change with temperature for compound 1 are given in Figure 7. The obtained data shows that the entropy, heat capacity, and enthalpy changes increase with the increasing of temperature (100 to 1000 K). This is due to the molecular vibrational moments occurring and intensified at high temperature [64]. The calculated thermodynamic functions vs temperature with regression factor (R2) are not less than 0.999 for all compounds 1-5. The corresponding fitting equations for compounds 1-5 are For compound 1, Cp = 11.1043 + 1.1878T – 5.1105×10-4 T2 R2 = 0.9994 S = 276.6924 + 1.2384T – 2.7869×10-4 T2 R2 = 0.9999 ∆H = -13.8385 + 0.1404T + 3.1437×10-4 T2 R2 = 0.9994 For compound 2, Cp = 24.2911 + 1.2777T – 5.6447×10-4 T2 R2 = 0.9995 S = 293.0813 + 1.4005T – 3.4369×10-4 T2 R2 = 0.9999 ∆H = -16.1186 + 0.1682T + 3.2895×10-4 T2 R2 = 0.9994 For compound 3, Cp = 19.2660 + 1.2522T – 5.2999×10-4T2 R2 = 0.9994 S = 288.7109 + 1.3467T – 3.1110×10-4T2 R2 = 0.9999 ∆H = -14.5778 + 0.1533T + 3.3627×10-4T2 R2 = 0.9995 For compound 4, Cp = 22.3297 + 1.2057 – 5.3285×10-4 T2 R2 = 0.9996 S = 280.4842 + 1.3193 – 3.2353×10-4 T2 R2 = 0.9999 ∆H = -15.3265 + 0.1584 + 3.1004×10-4 T2 R2 = 0.9994 For compound 5, Cp = 21.4665 + 1.2088 – 5.3522×10-4 T2 R2 = 0.9996 S = 285.6887 + 1.318 – 3.2243×10-4 T2 R2 = 0.9999 ∆H = -15.3249 + 0.1582 + 3.1026×10-4 T2 R2 = 0.9994 It is seen from Table 6 that the trend of total energy and zero-point energy of the compounds 1-5: 3 > 2 > 1 > 4 > 5. The thermodynamic parameters like heat capacity, entropy, and enthalpy obtained at different temperatures are specified in decreased order: 2 > 3 > 5 > 4 > 1. From Figure 7, it clearly reveals that the differences in entropy, heat capacity at constant pressure, and enthalpy change between compounds 1-3 are very small in magnitude and not significant. 4. Conclusion Five substituted 3-(1-((benzoyloxy)imino)ethyl)-2H- chromen-2-ones (1-5) have been synthesized using 3-(1- (hydroxyimino)ethyl)-2H-chromen-2-one and substituted benzoic acids in presence of POCl3 in pyridine. The calculated vibrational frequencies are matched well with the experimental results. The modes of vibrational assignment are allocated on the basis of PED calculations. The energy gap between HOMO and LUMO are in the trend of compounds 2 > 5 > 3 > 1 > 4. Smaller, the energy gap of compound 2 reveals more reactive than the other compounds 1, 3-5. The NBO analysis reveals that the electron density of conjugated π-π* bonds of the benzoyl group and benzene ring of coumarin have clearly demonstrated strong delocalization. The calculated first hyperpolarizability value (β) of compound 2 is virtually fifteen times superior to the urea while the other compounds are in 6, 2.2, and 1.6. The thermodynamic parameters viz., entropy, heat capacity, and enthalpy changes are increased with increasing temperature from 100 to 1000 K. These increasing thermodynamic Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 145 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 parameters may be the molecular vibrational intensities increase with temperature. Supporting information CCDC-1036818 contains the supplementary crystallo- graphic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/, or by e- mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Kannan Gokula Krishnan https://orcid.org/0000-0002-8223-557X Venugopal Thanikachalam https://orcid.org/0000-0002-2098-2641 References [1]. Balandrin, M. F.; Klocke, J. A.; Wurtele, E. S.; Bollinger, W. H. Science 1985, 228, 1154–1160. [2]. Murray, R. D. H.; Mendez, J.; Brown, S. A. The Natural Coumarins: Occurance; Chemistry and Biochemistry, Wiley: New York, 1982. [3]. Sandhu, S.; Bansal, Y.; Silakari, O.; Bansal, G. Bioorg. Med. Chem. 2014, 22, 3806–3814. [4]. Bhat, M. A.; Al-Omar, M. A.; Siddiqui, N. Med. Chem. Res. 2013, 22, 4455–4458. [5]. Lacy, A.; O’Kennedy, R. Curr. Pharm. Des. 2004, 10, 3797–3811. [6]. Arora, R. B.; Mathur, C. N. Br. J. Pharmacol. Chemother. 1963, 20, 29– 35. [7]. Singh, I. P.; Bharate, S. B.; Bhutani, K. K. Curr. Sci. 2005, 89, 269–290. [8]. Leal, L. K.; Ferreira, A. A.; Bezerra, G. A.; Matos, F. J.; Viana, G. S. J. Ethnopharmacol. 2000, 70, 151–159. [9]. Tyagi, Y. K.; Kumar, A.; Raj, H. G.; Vohra, P.; Gupta, G.; Kumari, R.; Kumar, P.; Gupta, R. K. Eur. J. Med. Chem. 2005, 40, 413–420. [10]. Wang, Z.-S.; Hara, K.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Suga, S.; Arakawa, H.; Sugihara, H. J. Phys. Chem. B 2005, 109, 3907–3914. [11]. Huang, Q.; Bao, C.; Ji, W.; Wang, Q.; Zhu, L. J. Mater. Chem. 2012, 22, 18275–18282. [12]. Bazzicalupi, C.; Caltagirone, C.; Cao, Z.; Chen, Q.; Di Natale, C.; Garau, A.; Lippolis, V.; Lvova, L.; Liu, H.; Lundström, I.; Mostallino, M. C.; Nieddu, M.; Paolesse, R.; Prodi, L.; Sgarzi, M.; Zaccheroni, N. Chemistry 2013, 19, 14639–14653. [13]. Rong, L.; Liu, L.-H.; Chen, S.; Cheng, H.; Chen, C.-S.; Li, Z.-Y.; Qin, S.-Y.; Zhang, X.-Z. Chem. Commun. (Camb.) 2014, 50, 667–669. [14]. Secci, D.; Carradori, S.; Bolasco, A.; Chimenti, P.; Yáñez, M.; Ortuso, F.; Alcaro, S. Eur. J. Med. Chem. 2011, 46, 4846–4852. [15]. Matos, M. J.; Vazquez-Rodriguez, S.; Uriarte, E.; Santana, L.; Viña, D. Bioorg. Med. Chem. Lett. 2011, 21, 4224–4227. [16]. Politzer, P.; Murray, J. S. The Chemistry of Hydroxylamines, Oximes and Hydroxamic Acids; Wiley, West Sussex, 2009. [17]. Krishnan, G., K.; Sivakumar, R.; Thanikachalam, V. J. Serb. Chem. Soc. 2015, 80, 1101–1111. [18]. Karakurt, A.; Alagöz, M. A.; Sayoğlu, B.; Calış, U.; Dalkara, S. Eur. J. Med. Chem. 2012, 57, 275–282. [19]. Bachovchin, D. A.; Wolfe, M. R.; Masuda, K.; Brown, S. J.; Spicer, T. P.; Fernandez-Vega, V.; Chase, P.; Hodder, P. S.; Rosen, H.; Cravatt, B. F. Bioorg. Med. Chem. Lett. 2010, 20, 2254–2258. [20]. Sun, R.; Li, Y.; Lü, M.; Xiong, L.; Wang, Q. Bioorg. Med. Chem. Lett. 2010, 20, 4693–4699. [21]. Liu, X.-H.; Pan, L.; Tan, C.-X.; Weng, J.-Q.; Wang, B.-L.; Li, Z.-M. Pestic. Biochem. Physiol. 2011, 101, 143–147. [22]. Hwu, J. R.; Tsay, S.-C.; Hong, S. C.; Hsu, M.-H.; Liu, C.-F.; Chou, S.-S. P. Bioconjug. Chem. 2013, 24, 1778–1783. [23]. Frisch, M. J.; Trucks G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; A. J. Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc. , Gaussian 09, Revision A. 02, Wallingford CT, 2009. [24]. Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B Condens. Matter 1988, 37, 785– 789. [25]. Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. [26]. Rauhut, G.; Pulay, P. J. Phys. Chem. 1995, 99, 3093–3100. [27]. Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502–16513. [28]. Wolinski, K.; Hinton, J. F.; Pulay, P. J. Am. Chem. Soc. 1990, 112, 8251– 8260. [29]. Krishnan, K.; Sivakumar, R.; Thanikachalam, V. Lett. Org. Chem. 2015, 12, 31–37. [30]. Wang, H.; Xu, S.-H.; Zeng, Z.; Zhang, Y.-H. Acta Crystallogr. Sect. E Struct. Rep. Online 2010, 66, o511. [31]. Vazquez-Rodriguez, S.; Uriarte, E.; Santana, L. Acta Crystallogr. Sect. E Struct. Rep. Online 2013, 69, o345. [32]. Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1-S19. [33]. Silverstein, R. M.; Webster, F. X.; Kiemle, D. J. The spectrometric identification of organic compounds: International edition; 7th ed.; John Wiley & Sons: Nashville, TN, 2005. [34]. Arjunan, V.; Sakiladevi, S.; Marchewka, M. K.; Mohan, S. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2013, 109, 79–89. [35]. Krishnan, K. G.; Sivakumar, R.; Thanikachalam, V.; Saleem, H.; Arockia doss, M. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2015, 144, 29–42. [36]. Arivazhagan, M.; Subhasini, V. P.; Kavitha, R. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2014, 128, 527–539. [37]. Palm, A.; Werbin, H. Can. J. Chem. 1953, 31, 1004–1008. [38]. Stuart, B. H. Infrared Spectroscopy: Fundamentals and Applications; John Wiley and Sons: Chichester, UK, 2004. [39]. Mariappan, G.; Sundaraganesan, N. J. Mol. Struct. 2014, 1063, 192–202. [40]. Ayyappan, S.; Sundaraganesan, N.; Kurt, M.; Sertbakan, T. R.; Özduran, M. J. Raman Spectrosc. 2010, 41, 1379–1387. [41]. Alcolea Palafox, M. Int. J. Quantum Chem. 2000, 77, 661–684. [42]. Krishnan, K. G.; Kumar, C. U.; Lim, W.-M.; Mai, C.-W.; Thanikachalam, P. V.; Ramalingan, C. J. Mol. Struct. 2020, 1199, 127037. [43]. Socrates, G. Infrared and Raman characteristic group frequencies: Tables and charts; 3rd ed.; John Wiley & Sons: Chichester, England, 2004. [44]. Snyder, R. G.; Strauss, H. L.; Elliger, C. A. J. Phys. Chem. 1982, 86, 5145– 5150. [45]. Karuppasamy, A.; Gokula Krishnan, K.; Pillai Velayutham Pillai, M.; Ramalingan, C. J. Mol. Struct. 2017, 1128, 674–684. [46]. Stalindurai, K.; Gokula Krishnan, K.; Nagarajan, E. R.; Ramalingan, C. J. Mol. Struct. 2017, 1130, 633–643. [47]. Muthu, S.; Ramachandran, G.; Uma maheswari, J. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2012, 93, 214–222. [48]. Clarkson, J.; Smith, W. E.; Batchelder, D. N.; Smith, D. A.; Coats, A. M. J. Mol. Struct. 2003, 648, 203–214. [49]. Mulliken, R. S. J. Chem. Phys. 1955, 23, 1841–1846. [50]. Santamaria, R.; Cocho, G.; Corona, L.; González, E. Chem. Phys. 1998, 227, 317–329. [51]. Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736–1740. [52]. Snehalatha, M.; Ravikumar, C.; Hubert Joe, I.; Sekar, N.; Jayakumar, V. S. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2009, 72, 654–662. [53]. Cramer, C. J. Essentials of Computational Chemistry: Theories and Models, 2nd Ed., Wiley, Hoboken, NJ, 2004. [54]. Udaya Sri, N.; Chaitanya, K.; Prasad, M. V. S.; Veeraiah, V.; Veeraiah, A. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2012, 97, 728–736. [55]. Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2013, 101, 370–381. [56]. Basri, R.; Khalid, M.; Shafiq, Z.; Tahir, M. S.; Khan, M. U.; Tahir, M. N.; Naseer, M. M.; Braga, A. A. C. ACS Omega 2020, 5, 30176–30188. [57]. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvyan, J. R. Introduction to Spectroscopy, 4th Ed., Brooks/Cole, Belmont, USA, 2009. [58]. Scrocco, E.; Tomasi, J. Electronic molecular structure, reactivity and intermolecular forces: An euristic interpretation by means of electrostatic molecular potentials. In Advances in Quantum Chemistry Volume 11; Elsevier, 1978; pp. 115–193. [59]. Nakano, M.; Shigemoto, I.; Yamada, S.; Yamaguchi, K. J. Chem. Phys. 1995, 103, 4175–4191. [60]. Cheng, L. T.; Tam, W.; Stevenson, S. H.; Meredith, G. R.; Rikken, G.; Marder, S. R. J. Phys. Chem. 1991, 95, 10631–10643. [61]. Wu, K.; Snijders, J. G.; Lin, C. J. Phys. Chem. B 2002, 106, 8954–8958. https://www.ccdc.cam.ac.uk/structures/ mailto:data_request@ccdc.cam.ac.uk https://orcid.org/0000-0002-8223-557X https://orcid.org/0000-0002-2098-2641 146 Krishnan and Thanikachalam / European Journal of Chemistry 12 (2) (2021) 133-146 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.133-146.2073 [62]. Zhang, J.; Xiao, H. J. Chem. Phys. 2002, 116, 10674–10683. [63]. Barone, V. J. Chem. Phys. 2004, 120, 3059–3065. [64]. Rastogi, V. K.; Jain, V.; Yadav, R. A.; Singh, C.; Palafox, M. A. J. Raman Spectrosc. 2000, 31, 595–603. Copyright © 2021 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. General procedure for the synthesis of 3-(1-((benzoyloxy)imino)ethyl)-2H-chromen-2-ones (1-5) 2.2. Single crystal X-ray crystallography 2.3. Spectral measurements 2.4. Computational details 3. Results and discussion 3.1. Synthesis 3.2. Molecular geometry 3.3. Vibrational analysis 3.3.1. C=O and C-O vibrations 3.3.2. C=N and N-O vibrations 3.3.3. C=C and C-C vibration 3.3.4. C-H vibration 3.3.5. Methyl group vibration 3.3.6. Nitro group vibration 3.3.7. C-Cl vibrations 3.4. Mulliken population analysis 3.5. NBO analysis 3.6. HOMO-LUMO analysis 3.7. NMR spectral analysis 3.8. Molecular electrostatic potential 3.9. Non-linear optical properties 3.10. Thermodynamic properties 4. Conclusion Supporting information Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField19: PrintField110: PrintField111: PrintField112: PrintField113: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: PrintField29: PrintField210: PrintField211: PrintField212: PrintField213: