Crystal structures, computational studies, and Hirshfeld surface analysis on 7-hydroxy-4-methyl-2H-chromen-2-one and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one European Journal of Chemistry 16 (3) (2025) 275-286 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2025 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.16.3.275-286.2674 European Journal of Chemistry View Journal Online View Article Online Crystal structures, computational studies, and Hirshfeld surface analysis on 7-hydroxy-4-methyl-2H-chromen-2-one and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one Felix Odame 1,*, Nathaniel Owusu Boadi 2, Salifu Nanga 1, Albert Aniagyei 1 and Eric Hosten 3 1 Department of Basic Sciences, School of Basics and Biomedical Sciences University of Health and Allied Sciences, PMB 31, Ho, Ghana 2 Department of Chemistry, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 3 Department of Chemistry, Nelson Mandela University, PO Box 77000, Gqeberha 6031, South Africa * Corresponding author at: Department of Basic Sciences, School of Basics and Biomedical Sciences University of Health and Allied Sciences, PMB 31, Ho, Ghana. e-mail: felixessah15@gmail.com (F. Odame). 10.5155/eurjchem.16.3.275-286.2674 Received: 15 February 2025 Received in revised form: 19 May 2025 Accepted: 15 June 2025 Published online: 30 September 2025 Printed: 30 September 2025 7-Hydroxy-4-methyl-2H-chromen-2-one and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2- one have been synthesized. The compounds have been characterized using IR, NMR, GC-MS, and elemental analysis. The single-crystal X-ray structure of the compounds showed that compound 1 was crystallized in the orthorhombic space group P212121 while compound 2 crystalized in the monoclinic space group P21/c. A comparison of the computed and experimental bond lengths and bond angles showed good agreement among the data. A Hirshfeld surface analysis showed that the H∙∙∙O/O∙∙∙H interaction was the most prominent molecular interaction for both compound 1 H∙∙∙O/O∙∙∙H (34.4%) and compound 2 H∙∙∙O/O∙∙∙H (48.6%). Crystal Coumarin Monoclinic Computation Orthorhombic Hirshfeld surface analysis Cite this: Eur. J. Chem. 2025, 16(3), 275-286 Journal website: www.eurjchem.com 1. Introduction Coumarins have been accessed by several methods, including the Perkin reaction, which involves the reaction of α,β-unsaturated aromatic acid in the presence of sodium acetate followed by intramolecular cyclization to give the expected coumarin [1], Knoevenagel condensation, which involves the reaction between salicylaldehydes and 1,3-dicar- bonyl compounds in the presence of a base or an energy source [2], Pechmann condensation, which involves the condensation of β-ketonic esters with phenols in the presence of concentrated sulfuric acid [3]. Wittig reaction, which involves an intra- molecular cyclisation of a substituted 2-formylphenyl 2- bromoacetate in saturated aqueous sodium bicarbonate [4], Baylis-Hillman reaction, which involves the reaction of 2- hydroxybenzaldehydes with the methyl acrylate in the presence of DABCO (1,4-diazabicyclo[2.2. 2]octane) [5]. Claisen rearrangement, which involves rearrangement of the 3,3- dimethylallyl ether in the presence of butyric anhydride, has been used to synthesize some coumarin compounds [6], and Vilsmeier-Haack and Suzuki cross-coupling reactions [1-8]. Coumarins have been reported to exhibit a wide spectrum of inhibitory properties [9-14]. They are known to have antibacterial [15-21] and antifungal activities [19,21-25]. Coumarins have also been reported to be anti-inflammatory [26,27], anti-HIV [10,28], anticancer [11,29,30], antituber- culosis [31], anticoagulant [32], antiviral [33] and antihyper- glycemic [34]. Several coumarin compounds have been reported to have appreciable antioxidant activity [35-38]. Coumarin derivatives are known as acetylcholinesterase inhibitors (AchE) inhibitors that can also be used to treat Alzheimer’s disease [39-41]. The nitro group has been reported to undergo tautomerism in certain scaffolds such as thiones [42]. Different methods have been used to study tautomerism, spectroscopy has been used to study tautomerism in some thiosemicarbazones, and it has been confirmed with DFT calculations [43]. Solvents and substituents have been reported to play an important role in tautomerism. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.16.3.275-286.2674 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.16.3.275-286.2674 mailto:felixessah15@gmail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.16.3.275-286.2674&domain=pdf&date_stamp=2025-09-30 276 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Scheme 1. Synthesis of 7-hydroxy-4-methyl-2H-chromen-2-one (1) and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one (2). In a study of substituents and solvent effects on the spectral properties of some substituted 4-hydroxycoumarin-derived compounds, the highest quantum fluorescence yield was observed to be apparent for scaffolds containing dimethyl- amino and acetamido groups as attachments to the phenyl ring [44]. This study reports the synthesis, crystal structures, and Hirshfeld surface analysis of 7-hydroxy-4-methyl-2H-chromen- 2-one and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one. A discussion of the XRD data of the compounds has been presented to provide insight into the structural properties of the compounds. Hirshfeld surface analysis has been performed on the compounds. The study is part of a continuing study on the development of xazepine-linked coumarins compounds as potential anticancer and antimicrobial agents. This work effectively confirms the basic scaffold on which the xazepine moiety can be mounted for testing. 2. Experimental 2.1. Reagents and instrumentation Analytical grade reagents and solvents for synthesis such as salicylaldehyde and ethyl acetoacetate were obtained from Sigma-Aldrich (USA), while ethanol and DMSO were obtained from Merck Chemicals (SA). The chemicals were used as received without further purification. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance AV 400 MHz spectrometer operating at 400 MHz for 1H and 100 MHz for 13C using DMSO-d6 as solvent and tetramethylsilane as internal standard. Chemical shifts are expressed in ppm. FT-IR spectra were recorded on a Bruker Platinum ATR Spectrophotometer Tensor 27. Elemental analyzes were performed using a Vario Elementar Microcube ELIII. Melting points were obtained using a Stuart Lasec SMP30 while the masses were determined using an Agilent 7890A GC System connected to a 5975C VL-MSC with electron impact as the ionization mode and detection by a triple-axis detector. The GC was fitted with a 30 m × 0.25 mm × 0.25 µm DB-5 capillary column. Helium was used as carrier gas at a flow rate of 1.63 mL/min with an average velocity of 30.16 cm/s and a pressure of 63.73 kPa. 2.2. Synthesis 2.2.1. 7-Hydroxy-4-methyl-2H-chromen-2-one (1) Resorcinol (37 g, 0.34 mol) and ethyl acetoacetate (45 mL) were dissolved in 200 mL of ethanol in a round bottom flask and placed in an ice bath. Concentrated sulfuric acid (150 mL) was added dropwise with stirring. Stirring was continued for 6 hours during which the reaction was monitored by thin-layer chromatography until the disappearance of the starting materials. The reaction mixture was then transferred to an ice bath and allowed to stand for four hours. The reaction mixture was filtered, dried, and the product recrystallized as a white solid in ethanol. Colour: White. Yield: 82%. M.p. = 189-190 °C. IR (νmax, cm−1): 3123 (OH), 1676 (C=O), 1598 (C=C), 1560 (C=C), 1449 (C-C), 1388 (C-O). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 10.51 (br, 1H, OH), 7.59 (d, 1H, J = 8.8 Hz, Ar-H), 6.80 (d, 1H, J = 8.8 Hz, 1H, Ar-H), 6.70 (1H, Ar-H), 6.11 (1H, Ar-H), 2.36 (s, 3H, CH3). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 161.6 (C=O), 160.9 (C=O), 155.4 (C), 154.0 (C), 127.1 (CH), 113.3 (CH), 112.5 (C), 110.7 (CH), 102.5 (CH), 18.7 (CH3). GC-MS (m/z, M+): 176.06, % 82.3. Anal. calcd. for C10H8O3: C, 68.18; H, 4.58; O, 27.25, Found: C, 68.10; H, 4.51; O, 27.18%. 2.2.2. 7-Hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1) (2) Compound 1 (10 g) was dissolved in 50 mL of ethanol, a mixture of HNO3 (5 mL) and H2SO4 (15 mL) was added dropwise with stirring for four hours, during which the reaction was monitored by thin layer chromatography until the disappearance of the starting material. The reaction mixture was transferred to an ice bath filtered and dried under vacuum. The product was dissolved in ethanol and extracted with acetic acid to obtain the 8-nitro derivative. The product was recrystallized and obtained as a yellow solid from DMSO: toluene (4:1, v:v) (Scheme 1). Color: Yellow. Yield: 79%. M.p.: 252-256 °C. IR (νmax, cm−1): 3282 (OH), 3055 (C–H), 1733 (C=O), 1616 (C=C), 1568 (C=C), 1506 (C=C), 1348 (C-N), 1322 (C-N). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 12.14 (br, 1H, OH), 8.25 (s, 1H, OH), 7.78 (d, J = 8.8 Hz, 1H, Ar-H), 7.56 (d, J = 8.8 Hz, 1H, Ar-H), 7.02 (d, J = 9.2 Hz, 1H, Ar-H), 6.80 (d, J =10.2 Hz, 1H, Ar- H), 6.59 (s, 1H, N-OH), 6.28 (s, 1H, Ar-H) 6.11 (s, 1H, Ar-H), 2.40 (s, 3H, CH3), 2.35 (s, 3H, CH3). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 161.61 (C=O), 160.74 (C=O), 158.54 (C), 155.28 (CH), 154.00 (CH), 152.85 (CH), 146.09 (C), 128.54 (CH), 127.03, (CH), 113.30 (CH), 112.44 (C), 111.72 (CH), 110.70 (CH), 102.62 (CH), 18.73 (CH3), 18.54 (CH3). GC-MS (m/z, M+): 221.09, %78.1. Anal. calcd. for C12H13NO6S: C, 48.16; H, 4.38; N, 4.68; Found: C, 48.07; H, 4.31; N, 4.60%. 2.3. X-ray crystallographic measurements Using a Bruker Kappa APEX II diffractometer and monochromated MoKα radiation (λ = 0.71073 Å), an X-ray diffraction investigation of the compounds was carried out at 200 K. Data collection was carried out using APEXII [45], and cell refinement and data reduction were carried out using SAINT software [46]. Using SHELXL [45] as a graphical interface, the structures were solved directly using SHELXS- 2013 [45] and then refined using least squares techniques using SHELXL-2013 [46]. Anisotropic refinement was used for all non-hydrogen atoms. Uiso (H) was set to 1.2Ueq (C) and carbon-bound H atoms were included in the refinement in the riding model approximation, with predicted positions (C-H = 0.95 Å for aromatic carbon atoms and C-H = 0.99 Å for methylene groups). With Uiso (H) set to 1.5Ueq (C), the H atoms of the methyl groups were allowed to spin around the C-C bond at a fixed angle to best fit the observed electron density (HFIX 137 in the SHELX program suite [46]). On the Fourier map, nitrogen-bound H atoms were found and could be freely refined. The numerical method used in SADABS was used to adjust the data for absorption effects [47]. ORTEP-3 [48] was used to create molecular visuals, while Mercury [49] and PLATON [50] were used to produce the publication data. Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 277 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Figure 1. Expanded 1H NMR spectrum of compound 2 indicating the doubling of the proton signals. 2.4. Computational studies The Gaussian 09 program was used to perform the calculations. Singlet ground state molecular geometries of all compounds were completely optimized in the gas phase in density functional theory (DFT) using the 6-311G(d,p) basis set and the B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals [51-53]. To ensure that the improved molecular structure matched the minimum energy, optimization and frequency calculation were performed. Gauss view 6.0 or Avogadro were used to view the results. The optimized frequencies were computed using the Gaussian 09 program [54]. The HOMO indicates the ability to donate an electron, while the LUMO indicates the ability to accept an electron. The energy of the HOMO is directly related to the ionization potential, while the energy of the LUMO is related to the electron affinity. The difference in energy between the HOMO and LUMO orbitals, which is the energy gap, decides the stability or reactivity of the molecules [55]. The energy gap is an important parameter in determining molecular electrical transport properties because it is a measure of electron conductivity [56]. The hardness of a molecule also corresponds to the energy gap between the HOMO and LUMO orbitals. The molecular electrostatic potential (MEP) gives a description of the potential energy that affects a unit positive charge (like a proton) when placed at a certain point in the environment of a molecule. [57-58] It gives maps of the electron density distribution of a molecule, revealing regions of positive and negative potential, which correspond to electrophilic and nucleophilic sites, respectively [59]. Contours of equal value in a selected plane are used to represent MEP values calculated around a molecule. 3. Results and discussion 3.1. Synthesis and reaction mechanism Compound 1 was obtained by the reaction of resorcinol with ethyl acetoacetate in the presence of an acid catalyst. The product was obtained as white crystals from ethanol. Compound 2 was obtained by reacting compound 1 with mixed acids (HNO3 and H2SO4). The 6-nitro and 8-nitro derivatives were separated by dissolving the dried product in ethanol and extracting with a mixture of toluene: acetic acid (60:40, v:v). The product was recrystallized as a yellow solid from DMSO: toluene mixture (4:1, v:v). 3.2. Spectroscopic characterization The IR spectrum of compound 1 showed the presence of an absorption peak at 3123 cm-1 for the aliphatic C-H stretch. Peaks were observed at 1676, 1598, 1560 and 1449 cm-1 for the C=O, C=C, C=C and C-O absorptions, respectively. The 1H NMR spectrum indicated the formation of a coumarin ring with the incorporation of the methyl group of ethyl acetoacetate confirmed by a signal at δ 2.36 ppm for three protons, a broad signal was observed at δ 10.51 ppm for the hydroxyl group, two singlet signals were observed at δ 6.70 and 6.11 ppm for two aromatic protons. In addition, two doublet signals were observed at δ 7.59 and 6.80 ppm for a proton each. The 13C NMR spectrum of compound 1 showed signals at δ 161.6 and 160.9 ppm for carbonyls. Signals observed at δ 155.4 and 154.0 ppm for aromatic carbons without hydrogen atoms were confirmed in the DEPT 135 spectrum. Four signals were observed at δ 127.1, 113.3, 112.5 and 110.7 ppm for aromatic carbons with protons attached. These signals confirmed the formation of the coumarin ring. A signal was also observed at 18.7 ppm for the incorporation of the methyl group on the coumarin ring. In compound 2, the IR spectrum confirmed a signal at 3282 cm-1 for the hydroxyl group, an absorption was observed at 3055 cm-1 for the aromatic C-H stretch, a signal at 1733 cm-1 was observed for the carbonyl of a lactone. Signals were observed at 1616, 1568 and 1506 cm-1 for the C=C stretch. Absorptions were observed at 1348 and 1322 cm-1 for the C-N stretch. The 1H NMR spectrum of compound 2 gave a broad signal at δ 12.14 ppm for the hydroxyl group. Four doublets were observed at δ 7.78, 7.56, 7.02 and 6.80 ppm, indicating a doubling of the peaks from the starting material. Three singlet signals were observed at δ 6.59, 6.28 and 6.11 ppm confirming the disappearance of the proton in the starting material, which has been occupied by the nitro group. The doubling of the peaks confirms the existence of two distinct species in the solution. The extra singlet signal is attributable to an OH signal emanating from the nitro group because of tautomerism. Two singlet signals were observed at δ 2.40 and 2.35 ppm confirming the incorporation of the methyl group. Figure 1 shows the expanded 1H NMR spectrum of compound 2 showing the doubling of the signals as a result of tautomerism of the nitro group. The 13C NMR of compound 2 gave signals at δ 161.6 and 160.7 ppm for carbonyl. Signals for aromatic carbons without hydrogen atoms were observed at δ 158.5, 155.3, 154.0, 152.9 and 146.1 ppm; this was confirmed by their absence in the DEPT135 spectrum. Signals were observed at δ 128.5, 127.0, 113.5, 113.3, 111.7 and 110.7 ppm for aromatic carbons having hydrogen atoms, these signals were confirmed by their presence in the DEPT spectrum. Two signals were observed at δ 18.7 and 18.5 ppm for the methyl groups. Scheme 2 gives the formation of tautomers in the nitrocoumarin derivative indicating the position of protonation of the possible tautomers. 3.3. Crystal structure analysis Compound 1 was recrystallized as white crystals from ethanol. The compound crystallized in the orthorhombic space group. 278 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 1. Crystal data and details of the structure refinement for compounds 1 and 2. Parameters Compound 1 Compound 2 Empirical formula C10H8O3 C12H13NO6S Formula weight (g/mol) 176.16 299.29 Temperature (K) 200(2) 296(2) Crystal system orthorhombic monoclinic Space group P212121 P21/c a (Å) 5.2105(2) 7.1648(7) b (Å) 11.7779(4) 20.229(2) c (Å) 13.1619(5) 9.5583(9) α (°) 90 90 β (°) 90 94.975(5) γ (°) 90 90 Volume (Å3) 807.73(5) 1380.1(2) Z 4 4 ρcalc (g/cm3) 1.449 1.440 μ (mm-1) 0.108 0.259 F(000) 368.0 624.0 Crystal size (mm3) 0.523 × 0.424 × 0.236 0.407 × 0.259 × 0.186 Radiation MoKα (λ = 0.71073) MoKα (λ = 0.71073) 2Θ range for data collection (°) 4.64 to 56.76 4.026 to 56.642 Index ranges -6 ≤ h ≤ 6, -14 ≤ k ≤ 15, -17 ≤ l ≤ 17 -9 ≤ h ≤ 9, 0 ≤ k ≤ 26, 0 ≤ l ≤ 12 Reflections collected 15752 3431 Independent reflections 2012 [Rint = 0.0158, Rsigma = 0.0101] 3431 [Rint = 0.0409, Rsigma = 0.0326] Data/restraints/parameters 2012/0/121 3431/36/222 Goodness-of-fit on F2 1.062 1.044 Final R indexes [I≥2σ (I)] R1 = 0.0291, wR2 = 0.0794 R1 = 0.0590, wR2 = 0.1522 Final R indexes [all data] R1 = 0.0304, wR2 = 0.0805 R1 = 0.0976, wR2 = 0.1783 Largest diff. peak/hole (e.Å-3) 0.25/-0.16 0.49/-0.27 CCDC 2419172 2419173 Figure 2. An ORTEP view of 7-hydroxy-4-methyl-2H-chromen-2-one (1). OHO O N OO OHO O N OHO DMSO in H2O 1a 1b 2a 2b 1c 2c 3a Scheme 2. Formation of tautomers in the nitrocoumarin derivative showing the position of protonation of the possible tautomers. P212121 with four molecules in the unit cell characterized by unit cell parameters a = 5.2105(2) (15) Å, b = 11.7779(4) Å, c = 13.1619(5) Å. Compound 2 was recrystallized as yellow crystals from DMSO:toluene (4:1, v:v). The compound crystallized in the monoclinic space group P21/c with four molecules in the unit cell characterized by unit cell parameters a = 7.1648(7) Å, b = 20.229(2) Å, c = 9.5583(9) Å, β=94.975(5)°. The ORTEP diag- rams for compounds 1 and 2 are presented in Figures 2 and 3. Crystallographic data, and selected bond lengths and bond angles for the compounds are provided in Tables 1 and 2. 3.4. Comparison of theoretical and experimental bond parameters for compound 1 Table 2 gives a summary of theoretical and experimental bond lengths and bond angles for compound 1 using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals and the 6- 311G (d, p) basis set. The bond lengths of O1-C2, O1-C10, O21- C2 and O81-C8, were experimentally determined as 1.367(2), 1.379(2), 1.220(2) and 1.353(2) Å, respectively, which is consistent with the C=O double bond [60-65], while the calculated bond lengths gave deviations between 0.001 and 0.026 Å from the experimental values. Additionally, the bond angles of C2-C3, C3-C4, C4-C5, C4-C41 and C5-C10 that were experimentally determined as 1.440(2), 1.354(2), 1.446(2), 1.503(2) and 1.402(2) Å, respectively, gave a deviation between 0.001 and 0.010 compared to the calculated bond lengths. The bond lengths of C5-C6, C6-C7, C7-C8, C8-C9 and C9-C10 which were 1.406(2), 1.376(2), 1.401(2), 1.391(2) and 1.386(2) Å, respectively, were consistent with C-C single bonds [60-65], recorded deviations between 0.001 and 0.009 Å when compared with the computed bond lengths. Crystallo- graphically determined bond angles C2-O1-C10, O1-C10-C9, C5- C10-C9, O1-C2-O21, O1-C10-C5 were observed at 121.3(1), 116.1(1), 122.9(1), 116.4(1) and 121.0(1)° while the calculated values gave deviations between 0.1 and 1.4°. Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 279 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 2. Summary of theoretical and experimental bond lengths (Å), and bond angles (°) for 7-hydroxy-4-methyl-2H-chromen-2-one (1) using B3LYP, CAM- B3LYP, B3PW91, wB97XD and M06 functionals and 6-311G(d,p) basis set (RMS: Root mean square, MAE: Mean absolute error). Bond lengths (Å) Experimental B3LYP CAM-B3LYP B3PW91 wB97XD M06 Min dev. Max dev. RMS MAE O1-C2 1.367(2) 1.400 1.385 1.394 1.384 1.391 0.016 0.033 0.0245 0.0238 O1-C10 1.379(2) 1.361 1.357 1.356 1.356 1.353 0.018 0.026 0.0225 0.0224 O21-C2 1.220(2) 1.208 1.203 1.207 1.203 1.203 0.012 0.017 0.0154 0.0152 O81-C8 1.353(2) 1.360 1.354 1.354 1.352 1.350 0.001 0.005 0.0035 0.0026 C2-C3 1.440(2) 1.453 1.454 1.450 1.456 1.448 0.008 0.016 0.0125 0.0122 C3-C4 1.354(2) 1.359 1.348 1.358 1.350 1.354 0.004 0.006 0.0043 0.0038 C4-C5 1.446(2) 1.451 1.452 1.448 1.453 1.445 0.001 0.007 0.0048 0.0042 C4-C41 1.503(2) 1.505 1.499 1.500 1.501 1.493 0.002 0.010 0.0052 0.0064 C5-C10 1.402(2) 1.410 1.399 1.407 1.400 1.403 0.001 0.008 0.0045 0.0042 C5-C6 1.406(2) 1.410 1.404 1.408 1.405 1.405 0.001 0.004 0.0023 0.0020 C6-C7 1.376(2) 1.383 1.377 1.381 1.379 1.378 0.001 0.007 0.0042 0.0036 C7-C8 1.401(2) 1.406 1.401 1.405 1.403 1.402 0.001 0.005 0.0030 0.0024 C8-C9 1.391(2) 1.394 1.387 1.392 1.389 1.389 0.001 0.004 0.0026 0.0024 C9-C10 1.386(2) 1.395 1.390 1.393 1.392 1.390 0.004 0.009 0.0063 0.0058 Bond angles (°) Experimental B3LYP CAM-B3LYP B3PW91 wB97XD M06 Min dev. Max dev. RMS MAE C2-O1-C10 121.3(1) 122.3 122.3 122.3 122.3 122.6 1.0 1.3 1.0668 1.06 O1-C10-C9 116.1(1) 116.3 116.2 116.2 116.1 116.4 0.1 0.3 0.1732 0.14 C5-C10-C9 122.9(1) 121.9 121.9 121.8 121.9 121.8 1.0 1.1 1.0412 1.04 O1-C2-O21 116.4(1) 117.5 117.8 117.5 117.7 117.6 1.1 1.4 1.2256 1.22 O1-C10-C5 121.0(1) 121.8 121.9 121.9 122.0 121.8 0.8 1.0 0.8832 0.88 O21-C2-C3 125.3(1) 126.6 126.1 126.5 126.0 126.6 0.7 1.3 1.0909 1.06 O1-C2-C3 118.3(1) 116.0 116.1 116.0 116.3 115.8 2.0 2.5 2.2658 2.26 C2-C3-C4 122.0(1) 123.2 123.0 123.2 123.0 123.2 1.0 1.2 1.1243 1.12 C3-C4-C41 121.2(1) 121.1 121.4 121.2 121.5 121.3 0.1 0.3 0.1732 0.16 C5-C4-C41 120.1(1) 120.2 119.9 120.2 119.9 120.0 0.1 0.2 0.1483 0.14 C3-C4-C5 118.7(1) 118.7 118.7 118.6 118.6 118.7 0.0 0.1 0.0632 0.20 C4-C5-C6 124.6(1) 124.7 124.6 124.7 124.6 124.6 0.0 0.1 0.0632 0.20 C4-C5-C10 118.6(1) 118.0 118.0 118.0 117.6 118.0 0.6 1.0 0.6986 0.68 C6-C5-C10 116.8(1) 117.3 117.4 117.3 117.4 117.4 0.5 0.6 0.5621 0.56 C5-C6-C7 121.5(1) 121.7 121.7 121.8 121.6 121.7 0.1 0.3 0.2098 0.20 C6-C7-C8 120.0(1) 119.5 119.5 119.5 119.5 119.5 0.0 0.5 0.5000 0.50 O81-C8-C9 122.6(1) 122.6 122.5 122.6 122.6 122.5 0.0 0.1 0.0632 0.04 C7-C8-C9 120.2(1) 120.4 120.4 120.3 120.4 120.5 0.1 0.3 0.2098 0.20 O81-C8-C7 117.2(1) 117.1 117.1 117.1 117.0 117.1 0.1 0.2 0.1265 0.12 C8-C9-C10 118.5(1) 119.2 119.1 119.2 119.1 119.1 0.6 0.7 0.6419 0.64 (a) (b) Figure 3. An ORTEP view and computationally optimized structure of 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1, v:v). Experimentally determined bond angles for O21-C2-C3, O1- C2-C3, C2-C3-C4, C3-C4-C41 and C5-C4-C41 which were 125.3(1), 118.3(1), 122.0(1), 121.2(1) and 120.1(1)° with the DFT calculated bond angles giving deviations between 0.1 and 2.5 °. Crystal data revealed that the bond angles of C3-C4-C5, C4- C5-C6, C4-C5-C10, C6-C5-C10 and C5-C6-C7 were experi- mentally determined as 118.7(1), 124.6(1), 18.6(1), 116.8(1) and 121.5(1)° with deviations between 0.001 and 1.0 ° representing the lowest and largest deviations, respectively, of the calculated values, from the experimental data. The bond angles of C4-C5-C10, C6-C5-C10, C5-C6-C7 and C6-C7-C8 were experimentally found to be 118.6(1), 116.8(1), 121.5(1) and 120.0(1)° while the computed values gave deviations between 0.1 and 1.0° from the experimental values. Crystal data revealed that the bond angles O81-C8-C9, C7-C8-C9, O81-C8-C7, and C8- C9-C10, which were 122.6(1), 120.2(1), 117.2(1) and 118.5(1)°, respectively, deviated from the calculated values by 0.1-0.7°. Table 3 gives the results of the linear regression for theoretical and experimental bond lengths and bond angles for 7-hydroxy-4-methyl-2H-chromen-2-one (1). Linear regression analyzes were performed between the experimental and theoretical bond lengths and bond angles of 7-hydroxy-4- methyl-2H-chromen-2-one (1), using five density functionals (B3LYP, CAM-B3LYP, B3PW91, wB97XD, and M06) with the 6- 311G(d,p) basis set. In these models, the experimental values were considered the dependent variable, whereas the theoretical values served as the independent variable. For the lengths of the bonds, all functionals exhibited strong linear correlations with the experimental data, with R2 values ranging from 0.971 to 0.980. The CAM-B3LYP and wB97XD functionals yielded the highest coefficients of determination (R2 = 0.980), indicating superior predictive performance. Slopes (b₁) were close to unity (0.912-0.937), suggesting a high degree of agreement. For the bond angles, the R2 values ranged from 0.902 to 0.918, with wB97XD again showing the best coefficient of determination (R² = 0.918). The slopes for the bond angles (0.866-0.900) indicate a modest compression in the predicted values, and the relatively higher intercepts (b₀ ≈ 12-16°) reflect minor systematic deviations. In general, the regression results confirm that all five functionals provide statistically significant and reliable predictions of the experimental data. 280 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 3. Linear regression for theoretical and experimental bond lengths (Å), and bond angles (°) for 7-hydroxy-4-methyl-2H-chromen-2-one (1) using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals and 6-311G(d,p) basis set. DFT functional (Bond lengths) b0 b1 p-value R2 B3LYP 0.095 0.928 < 0.00001 0.972 CAMB3LYP 0.112 0.920 < 0.00001 0.980 B3PW91 0.087 0.936 < 0.00001 0.973 wB97XD 0.122 0.912 < 0.00001 0.980 M06 0.089 0.937 < 0.00001 0.971 DFT functional (Bond angles) b0 b1 p-value R2 B3LYP 15.142 0.873 < 0.00001 0.916 CAMB3LYP 11.894 0.900 < 0.00001 0.915 B3PW91 15.316 0.872 < 0.00001 0.915 wB97XD 12.526 0.895 < 0.00001 0.918 M06 16.019 0.866 < 0.00001 0.902 Table 4. Summary of theoretical and experimental bond lengths (Å), and bond angles (°) for 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1) using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals and 6-311G(d,p) basis set (RMS: Root mean square, MAE: Mean absolute error). Bond lengths (Å) Experimental B3LYP CAM-B3LYP B3PW91 wB97XD M06 Min dev. Max dev. RMS MAE S1-C1 1.745(2) 1.824 1.804 1.812 1.807 1.807 0.059 0.079 0.066 0.066 S1-C2 1.639(2) 1.824 1.804 1.812 1.807 1.807 0.165 0.185 0.172 0.172 S1-O1 1.464(8) 1.535 1.526 1.529 1.519 1.519 0.055 0.071 0.062 0.062 S2-O2 1.455(1) 1.535 1.526 1.529 1.519 1.519 0.064 0.080 0.071 0.434 S2-C3 1.733(2) 1.824 1.804 1.811 1.807 1.807 0.071 0.091 0.078 0.078 S2-C4 1.640(2) 1.824 1.804 1.812 1.807 1.807 0.167 0.184 0.171 0.170 O14-C13 1.391(3) 1.406 1.390 1.399 1.349 1.389 0.100 0.042 0.020 0.014 O14-C21 1.364(3) 1.355 1.351 1.349 1.319 1.349 0.009 0.045 0.023 0.019 O22A-N22 1.233(4) 1.228 1.219 1.221 1.219 1.219 0.005 0.014 0.012 0.012 O22B-N22 1.181(4) 1.227 1.220 1.222 1.227 1.219 0.038 0.046 0.042 0.042 O23-C23 1.333(3) 1.333 1.327 1.328 1.464 1.327 0.005 0.131 0.059 0.030 N22-C22 1.455(3) 1.470 1.462 1.465 1.350 1.464 0.005 0.120 0.048 0.029 C11-C12 1.345(4) 1.358 1.348 1.357 1.501 1.350 0.001 0.143 0.070 0.038 C11-C16 1.492(4) 1.505 1.500 1.500 1.455 1.501 0.008 0.037 0.019 0.015 C12-C13 1.419(4) 1.452 1.453 1.449 1.393 1.455 0.030 0.026 0.032 0.032 C21-C22 1.386(3) 1.397 1.391 1.395 1.402 1.393 0.005 0.016 0.010 0.010 C21-C26 1.383(3) 1.411 1.400 1.408 1.396 1.402 0.013 0.028 0.021 0.020 C22-C23 1.392(3) 1.404 1.396 1.402 1.389 1.396 0.004 0.012 0.008 0.007 Bond angles (°) Experimental B3LYP CAM-B3LYP B3PW91 wB97XD M06 Min dev. Max dev. RMS MAE O1-S1-C1 106.3(7) 105.6 105.4 105.6 105.6 105.6 0.7 0.9 0.744 0.740 O1-S1-C2 112.9(8) 105.8 105.6 105.9 105.5 105.5 7.0 7.4 7.242 7.240 C1-S1-C2 101.3(8) 97.8 98.0 97.8 97.6 97.6 3.3 3.7 3.543 3.540 C3-S2-C4 104.8(11) 97.8 98.0 97.8 97.6 97.6 6.8 7.2 7.042 7.040 O2-S2-C3 107.6(11) 105.6 105.4 105.9 005.6 105.6 1.7 2.2 1.986 1.980 O2-S2-C4 109.9(10) 105.8 105.6 105.6 105.5 105.5 4.1 4.4 4.301 4.300 C13-O14-C21 120.8(2) 122.2 122.2 122.2 122.1 122.1 1.3 1.4 1.361 1.360 O22B-N22-C22 119.3(3) 117.2 117.1 117.1 117.1 117.1 2.1 2.2 2.180 2.180 O22A-N22-O22B 123.7(2) 125.8 126.7 125.9 125.8 125.8 2.1 3.0 2.327 2.300 O22A-N22-C22 117.0(2) 117.0 117.3 116.9 117.0 117.0 0.1 0.3 0.141 0.080 C12-C11-C26 118.6(2) 118.9 118.8 118.8 121.4 118.7 0.1 0.3 1.266 0.720 C16-C11-C26 119.9(2) 120.1 119.9 120.1 119.8 119.8 0.1 0.2 0.141 0.120 C12-C11-C16 121.6(2) 121.0 121.3 121.1 118.7 121.4 0.1 2.3 1.353 0.900 C11-C12-C13 123.2(3) 123.2 122.9 123.1 122.9 122.9 0.1 0.3 0.237 0.200 O15 -C13-C12 127.5(2) 126.8 126.3 126.7 126.2 126.9 0.1 0.4 0.961 0.920 O14-C13-C12 117.2(2) 115.8 116.0 115.9 116.1 116.1 0.1 0.3 1.226 1.220 O14-C13-O15 115.3(2) 117.4 117.7 117.4 117.6 117.6 0.2 0.3 2.243 2.240 C22-C21-C26 121.0(2) 120.5 120.5 120.4 120.4 120.4 0.0 0.1 0.562 0.560 O14-C21-C26 122.3(2) 122.1 122.2 122.4 122.4 122.4 0.1 0.3 0.126 0.120 O14-C21-C22 116.6(2) 117.4 117.3 117.3 117.2 117.2 0.1 0.2 0.684 0.680 N22-C22-C21 119.3(2) 119.7 119.6 108.9 119.6 119.6 0.1 0.8 4.660 2.340 C21-C22-C23 121.3(2) 121.3 121.3 121.4 121.4 121.4 0.1 0.3 0.077 0.060 N22-C22-C23 119.5(2) 119.0 119.0 118.9 119.0 119.0 0.0 0.1 0.522 0.520 C22-C23-C24 117.6(2) 118.2 118.2 118.1 118.2 118.2 0.0 01 0.581 0.580 O23-C23-C24 123.8(2) 123.1 123.1 123.3 123.2 123.2 0.0 0.1 0.624 0.620 O23-C23-C22 118.6(2) 118.6 118.7 123.5 118.5 118.5 0.1 4.9 2.193 1.040 C23-C24-C25 120.7(2) 120.3 120.2 120.4 120.1 120.1 0.1 0.3 0.494 0.480 3.5. Comparison of the theoretical and experimental bond parameters for compound 2 Table 4 gives a summary of theoretical and experimental bond lengths and bond angles for compound 2 using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals and 6- 311G(d,p) basis set. The bond lengths S1-C1, S1-C2, S1-O1, S2- O2, S2-C3 and S2-C4 for compound 2 were experimentally determined as 1.745(2), 1.639(2), 1.464(8), 1.455(1), 1.733(2) and 1.640(2) Å, respectively, while the calculated bond lengths gave deviations between 0.055 and 0.185 Å from the experimental values. The bond lengths of O14-C13, O14-C21, O22A-N22 and O22B-N22 were experimentally determined as 1.391(3), 1.364(3), 1.233(4) and 1.181(4) Å, respectively, while the computed values deviated by 0.009-0.100 Å from the experimental values. Crystallographically determined bond lengths of O23-C23, N22-C22, C11-C12 and C11-C16 were found at 1.333(3), 1.455(3), 1.345(4) and 1.492(4) Å while the computed values gave deviations between 0.005 and 0.143 Å. The bond lengths of C12-C13, C21-C22, C21-C26 and C22-C23 were experimentally determined as 1.419(4), 1.386(3), 1.383(3) and 1.392(3) Å with deviations between 0.004 and 0.030 Å representing the lowest and largest deviations, respectively, from the experimental values. Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 281 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 5. Linear regression for theoretical and experimental bond lengths (Å), and bond angles (°) for 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1) using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 functionals and 6-311G(d,p) basis set. DFT functional (Bond lengths) b0 b1 p-value R2 B3LYP 0.314 0.758 < 0.00001 0.955 CAMB3LYP 0.293 0.777 < 0.00001 0.957 B3PW91 0.301 0.770 < 0.00001 0.956 wB97XD 0.363 0.730 < 0.00001 0.852 M06 0.298 0.774 < 0.00001 0.958 DFT functional (Bond angles) b0 b1 p-value R2 B3LYP 26.398 0.781 < 0.00001 0.948 CAMB3LYP 26.849 0.777 < 0.00001 0.943 B3PW91 32.350 0.731 < 0.00001 0.877 wB97XD 27.603 0.771 < 0.00001 0.932 M06 27.284 0.773 < 0.00001 0.946 (a) (b) (c) (d) (e) (f) Figure 4. Hirshfeld surfaces mapped for (a) dnorm surfaces, (b) shape index, (c) curvedness, (d) di, (e) de, and (f) fragment patch of compound 1. The bond angles of O1-S1-C1, O1-S1-C2, C1-S1-C2, C3-S2- C4, O2-S2-C3 and O2-S2-C4 were experimentally found to be 106.3(7), 112.9(8), 101.3(8), 104.8(11), 107.6(11) and 109.9(10)°, while the computed values gave deviations of between 0.7 and 7.2° from the experimental values. Crystal data revealed that bond angles of C13-O14-C21, O22B-N22-C22, O22A-N22-O22B, O22A-N22-C22 and C12-C11-C26, were 120.8(2), 119.3(3), 123.7(2), 117.0(2) and 118.6(2), respectively, they deviated from the calculated values by 0.1- 2.3°. The bond angles of C16-C11-C26, C12-C11-C16, C11-C12- C13, O15 -C13-C12 and O14-C13-C12 were experimentally determined as 119.9(2), 121.6(2), 123.2(3), 127.5(2) and 117.2(2) (1)°, while the computed values gave deviations of between 0.1 and 2.3° from the experimental values. Crystal structure data gave the experimentally determined bond angles for O14-C13-O15, C22-C21-C26, O14-C21-C26, O14-C21-C22 and N22-C22-C21 as 115.3(2), 121.0(2), 122.3(2), 116.6(2) and 119.3(2) respectively, which deviated from the computed values by 0.1 to 0.8°. The bond angles of N22-C22-C23, C22- C23-C24, O23-C23-C24, O23-C23-C22 and C23-C24-C25 were experimentally determined as 119.5(2), 117.6(2), 123.8(2), 118.6(2) and 120.7(2)°, while the computed values gave deviations of between 0.1 and 4.9° from the experimental data. Linear regression analyses between experimental and theoretical bond lengths and bond angles of the 7-hydroxy-4- methyl-8-nitro-2H-chromen-2-one-(methylsulfinyl) methane (1:1) complex were performed using five DFT methods (B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06) with the 6-311G(d,p) basis set. All models demonstrated statistically significant correlations (p < 0.00001). For the lengths of the bonds, the M06 functional showed the best predictive performance (R2 = 0.958), closely followed by CAM-B3LYP and B3PW91. The slopes ranged from 0.730 to 0.777, with minor systematic deviations indicated by intercepts between 0.293 and 0.363. In the case of bond angles, B3LYP and M06 yielded the highest R2 values (0.948 and 0.946, respectively), with slopes between 0.731 and 0.781 and relatively higher intercepts (26.398- 32.350°), suggesting consistent underprediction and slight systematic offsets. Overall, the M06 and CAM-B3LYP functionals offered the most reliable agreement with the experimental data for bond lengths, while B3LYP and M06 provided the best predictions for bond angles. Table 5 shows the results of the linear regression for the theoretical and experimental bond lengths (Å), and bond angles (°) for the 7- hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1) (2). 3.6. Hirshfeld surface analysis A quantitative method for examining the interactions between molecules in a crystal structure is Hirshfeld surface analysis. Their crystal-packing behavior is described in depth. Crystal Explorer 3.1 software was used to map fingerprint plots and Hirshfeld surfaces [66]. The normalized contact distance (dnorm), which was calculated using the following equation and acquired with a high surface resolution and static color scale, served as a visual representation of the analysis. According to Equation 1, rvdw is the atom’s van der Waals radius, and de is the distance between the Hirshfeld surface and the closest nucleus outside the surface, and di is the corresponding distance between the nearest nucleus inside the surface [67]. The parameter dnorm is described by the surface with a red, white, and blue color scheme [68-70]. Inter- molecular interactions shorter than their vdW radii are indicated by bright red spots, whereas those longer than their vdW radii are indicated by blue spots. Their vdW radii add up to the white patches. 282 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 All∙∙∙All (100%) H···C/C···H (30.9%) H···H/H···H (28.2%) O···O/O···O (2.1%) H···O/O···H (34.4%) O···C/C···O (5.5%) Figure 5. Relative contributions to the percentage of Hirshfeld surface area for the various intermolecular contacts for compound 1. (a) (b) (c) (d) (e) (f) Figure 6. Hirshfeld surfaces mapped for (a) dnorm surfaces, (b) shape index, (c) curvedness, (d) di, (e) de and (f) fragment patch of compound 2. 𝑑𝑑𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 = 𝑑𝑑𝑖𝑖− rivdw rivdw + 𝑑𝑑𝑒𝑒− revdw revdw (1) Figure 4 shows the molecular Hirshfield surfaces that were created using a standard (high) surface resolution. These surfaces include the dnorm surface, shape index, and curvedness of compound 1. Although di was mapped throughout the range of 0.6837 to 2.6269 Å, the dnorm surface was mapped on over the range of -0.6918 to 1.2749 Å. The shape index ranged from - 1.0000 to 1.0000 Å, the fragment patch from 0.0000 to 13.0000 Å, the curvature from -4.0000 to 0.4000 Å, and the parameter de was between 0.6813 and 2.5157 Å. The two-dimensional (2D) fingerprint plots from the Hirshfeld surface analyses of compound 1 are shown in Figure 5. They show the relative contribution (in percentage) of the major intermolecular contacts associated with it. Furthermore, the C-H (30.9%) and O-H (34.4%) fingerprint plots also provide information about the intermolecular hydrogen bonds and the contribution of the individual elements toward crystal packing. The 2D fingerprint plots complement the Hirshfeld surface by providing quantitative information on the nature and type of intermolecular contacts. The most significant interaction is H- H, which contributes 28.2% to the overall crystal packing. One of the most important connections is the H-H interaction, which is represented by a single spike. Weak C-H∙∙∙π interactions are the cause of the distinctive "wings" shown in the fingerprint plot of C-H contacts. On the form index, the blue triangles, which are represented by convex regions, show the ring atoms of the molecule inside the surface, while the red triangles, which are represented by concave regions, show π-stacking interactions. According to the 2D fingerprint plot, the C-H∙∙∙π interactions, represented by the red triangles on the shape index mapping, have a contribution of 30.9%. The electron density of the surface curves around the chemical interactions, as indicated by the curvedness. Whereas strong curvature areas, which often tend to divide the surface into patches and indicate connections between nearby molecules, correlate with high values of curvedness, flat areas of the surface correspond to low levels of curvedness. π∙∙∙π stacking interactions are indicated by a broad and flat area with a blue boundary. This molecule exhibits π∙∙∙π stacking interactions to some extent. Molecular Hirshfield surfaces comprising of dnorm surface, shape index, and curvedness of compound 1 were generated using a standard (high) surface resolution and are illustrated in Figure 6. Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 283 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 6. HOMO-LUMO of compound 1 using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 with the 6-311G(d,p) basis set. B3LYP CAM-B3LYP B3PW91 Wb97XD M06 LUMO HOMO All∙∙∙All (100%) C∙∙∙C/C∙∙∙C (7.6%) H∙∙∙C/C∙∙∙H (6.0%) O∙∙∙C/C∙∙∙O (2.9%) H∙∙∙H/H∙∙∙H (29.8%) H∙∙∙O/O∙∙∙H (48.6%) H∙∙∙S/S∙∙∙H (2.0%) O∙∙∙O/O∙∙∙O (2.1%) Figure 7. Relative contributions to the percentage of Hirshfeld surface area for the various intermolecular contacts for compound 2. The dnorm surface was mapped on over the range of -0.2061 to 1.1877 Å, while di was mapped over the range of 0.9488 to 2.4042 Å. The parameter de was in the range of 0.9497 to 2.4758 Å, the shape index ranging from -1.0000 to 1.0000 Å, fragment patch 0.0000 to 32.0000 Å and curvature lying between -4.0000 to 0.4000 Å. The two-dimensional (2D) fingerprint plots of compound 2 from Hirshfeld surface analysis are shown in Figure 7. It displays the proportional share (in percentage) of the main intermolecular interactions that are connected to it. By offering quantitative data on the kind and nature of intermolecular interactions, the 2D fingerprint plots enhance the Hirshfeld surface. O-H is the most significant interaction, accounting for 48.6% of the total crystal packing. Furthermore, information regarding intermolecular hydrogen bonds and the different elements' contributions to the crystal packing may be found in the C-H (6.0%) and H-H (29.8%) fingerprint plots. Flat and sparse taperings in the fingerprint pattern of C-H contacts are compatible with very weak C-H∙∙∙π interactions. On the form index, the blue triangles, which are represented by convex regions, show the ring atoms of the molecule inside the surface, while the red triangles, which are represented by concave regions, show π-stacking interactions. The electron density of the surface curves around the chemical interactions, as indicated by the curvedness. Whereas strong curvature areas, which often tend to divide the surface into patches and indicate connections between nearby molecules, correlate with high values of curvedness, flat areas of the surface correspond to low levels of curvedness. π∙∙∙π stacking interactions are indicated by a broad and flat area with a blue boundary. Curvedness indicates that there are no π∙∙∙π stacking interactions in this molecule. 3.7. HOMO-LUMO analysis Table 6 shows the computed HOMO-LUMO energies for 7- hydroxy-4-methyl-2H-chromen-2-one (1). The frontier orbitals of compound 1 shows that the HOMO is delocalized over the entire molecule except the methyl group and some hydrogen atoms, while the LUMO is largely delocalized over the entire molecule except some hydrogen atoms. This indicates that during charge transfer in a reaction, the molecule is stabilized by delocalization of electrons over the entire molecule, which also confirms the susceptibility of some protons to substitution reaction. The delocalization of electrons in the HOMO and LUMO is consistent for all functionals and basis set except for a minor difference in orbital distribution. Table 7 gives the computed HOMO-LUMO energies for compound 2. HOMO is delocalized over 7-hydroxy-4-methyl-8- nitro-2H-chromen-2-one with the exception of two protons on the methyl group and some protons on the coumarin ring with no contribution from methylsulfinyl)methane, while the LUMO is delocalized over the coumarin ring except the methyl group with partial contribution from the nitro group but no contribution from the dimethylsulfoxide group. 3.8. Molecular electrostatic potential maps The electrostatic potential shows static charge distributions on a molecule. 284 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 Table 7. HOMO-LUMO of compound 2 using B3LYP, CAM-B3LYP, B3PW91, wB97XD and M06 with the 6-311G(d,p) basis set. B3LYP CAM-B3LYP B3PW91 wB97XD M06 LUMO HOMO (a) (b) (c) Figure 8. Molecular electrostatic potential maps (isosurface value = 0.02 au) of 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methyl sulfinyl)methane (1:1) calculated at (A) B3LYP/6-311G(d,p), (B) M06/6-311G(d,p), (C) ωB97X-D/6-311G(d,p) level of theory. The red surface corresponds to a region of negative electrostatic potential, whereas the blue color corresponds to the positive potential. Positive and negative potentials in kJ/mol. This property has been beneficial for analyzing and predicting molecular reactive behavior, indicating sites or regions of a molecule where an approaching electrophile/ nucleophile is initially attracted. The MEP was calculated to predict reactive sites for electrophilic and nucleophilic attack for the 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one com- pound with (methyl sulfinyl) methane (1:1) studied. The positive regions (blue) are related to nucleophilic reactivity, and the negative regions (red) to electrophilic reactivity, shown in Figure 8. 4. Conclusions 7-Hydroxy-4-methyl-2H-chromen-2-one (compound 1) and 7-hydroxy-4-methyl-8-nitro-2H-chromen-2-one (com- pound 2) were synthesized and characterized using IR, NMR, GC-MS, and microanalysis. Compound 1 crystallized in the orthorhombic space group P212121, while compound 2 crystallized in the monoclinic space group P21/c, according to the compound’s single-crystal X-ray structure. The non- classical hydrogen bonding network holds the four molecules in each of the compounds' unit cells together. The computed and experimental data showed good internal consistency upon comparison. Linear regression analysis of the calculated and experimental parameters for compound 1 indicated that the functionals CAM-B3LYP and wB97XD produced the highest determination coefficients (R2 = 0.980), indicating better predictive performance. For compound 2, the bond lengths were highly consistent with experimental data, while the regression analysis for the bond angles showed greater variability among the functionals. CAM-B3LYP gave the best agreement with the experiment (R² = 0.873, b₁ = 0.765), while wB97XD and M06 showed the weakest correlations. Acknowledgements The authors acknowledge the Centre for High Performance Computing in South Africa for the use of their computing resources (CHEM1261). Supporting information CCDC-2419172 and 2419173 contain the supplementary crystallographic 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. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Felix Odame; Methodology: Felix Odame; Software: Eric Hosten, Felix Odame; Validation: Eric Hosten, Felix Odame; Formal Analysis: Eric Hosten, Felix Odame, Albert Aniagyei, Nathaniel Owusu Boadi; Investigation: Felix Odame, Resources: Felix Odame; Data Curation: Felix Odame; Statistical analysis : Salifu Nanga; Writing - Original Draft: Felix Odame; Writing - Review and Editing: Felix Odame, Salifu Nanga, Nathaniel Owusu Boadi; Visualization: Felix Odame; Supervision: Felix Odame; Project Administration: Felix Odame. ORCID and Email Felix Odame felixessah15@gmail.com https://orcid.org/0000-0001-7651-8816 Nathaniel Owusu Boadi noboadi@gmail.com https://orcid.org/0000-0003-2673-7011 Salifu Nanga snanga@uhas.edu.gh https://orcid.org/0000-0002-3712-5013 Albert Aniagyei aaniagyei@uhas.edu.gh https://orcid.org/0000-0002-9699-9300 Eric Hosten eric.hosten@mandela.ac.za https://orcid.org/0000-0003-4173-2550 https://www.ccdc.cam.ac.uk/structures/ mailto:data_request@ccdc.cam.ac.uk mailto:data_request@ccdc.cam.ac.uk mailto:felixessah15@gmail.com https://orcid.org/0000-0001-7651-8816 mailto:noboadi@gmail.com https://orcid.org/0000-0003-2673-7011 mailto:snanga@uhas.edu.gh https://orcid.org/0000-0002-3712-5013 mailto:aaniagyei@uhas.edu.gh https://orcid.org/0000-0002-9699-9300 mailto:eric.hosten@mandela.ac.za https://orcid.org/0000-0003-4173-2550 Odame et al. / European Journal of Chemistry 16 (3) (2025) 275-286 285 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.3.275-286.2674 References [1]. 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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 (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). https://doi.org/10.1002/wcms.1601 https://core.ac.uk/download/pdf/224300821.pdf https://doi.org/10.1038/s41598-019-56331-z https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Experimental 2.1. Reagents and instrumentation 2.2. Synthesis 2.2.1. 7-Hydroxy-4-methyl-2H-chromen-2-one (1) 2.2.2. 7-Hydroxy-4-methyl-8-nitro-2H-chromen-2-one compound with (methylsulfinyl)methane (1:1) (2) 2.3. X-ray crystallographic measurements 2.4. Computational studies 3. Results and discussion 3.1. Synthesis and reaction mechanism 3.2. Spectroscopic characterization 3.3. Crystal structure analysis 3.4. Comparison of theoretical and experimental bond parameters for compound 1 3.5. Comparison of the theoretical and experimental bond parameters for compound 2 3.6. Hirshfeld surface analysis 3.7. HOMO-LUMO analysis 3.8. Molecular electrostatic potential maps 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField19: PrintField110: PrintField111: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: PrintField29: PrintField210: PrintField211: