Study of hydrogen bonds in N-methylacetamide by DFT calculations of oxygen, nitrogen, and hydrogen solid-state NMR parameters

Solid-state nuclear magnetic resonance (NMR) parameters of ¹⁷O, ¹⁴N/¹⁵N, and ²H/¹H nuclei were evaluated in two available neutron crystalline structures of N-methylacetamide (NMA) at 250 and 276 K, NMA-I and NMA-II, respectively. Density functional theory calculations were performed by B3LYP method and 6-311++G** and IGLO-II type basis sets to calculate the electric field gradient (EFG) and chemical shielding (CS) tensors at the sites of mentioned nuclei. In order to investigate hydrogen bonds (HBs) effects on NMR tensors, calculations were performed on four-model systems of NMA: an optimized isolated gas-phase, crystalline monomers, crystalline dimers, and crystalline trimers. Comparing the calculated results reveal the influence of N–H···O=C and C–H···O=C HB types on the NMR tensors which are observable by the evaluated parameters including quadrupole coupling constant, C _Q, and isotropic CS, σ _iso. Furthermore, the results demonstrate more influence of HB on the EFG and CS tensors of NMA at 276 K rather than that of 250 K.     

Efficient Synthesis of Dialkyl (2Z)‐2‐[(E)‐1‐Aryl‐2‐(3‐arylquinoxalin‐2‐yl)ethenyl]but‐2‐enedioates

The reaction of dialkyl acetylenedicarboxylates 4 with 1‐aryl‐2‐[(3‐arylquinoxalin‐2(1H)‐ylidene)ethanones 3 in the presence of Ph₃P leads to dialkyl (2Z)‐2‐[(E)‐1‐aryl‐2‐(3‐arylquinoxalin‐2‐yl)ethenyl]but‐2‐enedioates 1 in good yields.     

Stereoselective synthesis of dialkyl 3-spiroindanedione-1,2,3,3a-tetrahydropyrrolo[1,2-a]quinoline-1,2-dicarboxylates

The 1:1 intermediate generated by the addition of quinoline to dialkyl acetylenedicarboxylates is trapped by 1,3-indanedione to yield dialkyl 3-spiroindanedione-1,2,3,3a-tetrahydropyrrolo[1,2-a]quinoline-1,2-dicarboxylates in good yields. The structures of these products were confirmed by NMR and single-crystal X-ray diffraction studies.     

Piperazinediium,Zr(IV) and Ce(IV) pyridine-2,6-dicarboxylates: Syntheses,characterizations, crystal structures, ab initio HF,DFT calculations and solution studies

The novel title compounds, (pipzH₂)_1.5(pydcH)₃·3.7H₂O, 1, (pipzH₂)[Zr(pydc)₃]·8H₂O, 2 and (pipzH₂)[Ce(pydc)₃]·8H₂O, 3 in which pydcH₂ is pyridine-2,6-dicarboxylic acid and pipz is piperazine were obtained in aqueous solution. The compounds were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy, elemental analyses, and X-ray crystallography. Compound 1 is resulted from proton transfer between pydcH₂ and pipz. However, compounds 2 and 3 are resulted from complexation of 1 and corresponding metallic salts. Both compounds 2 and 3 contain three pyridine-2,6-dicarboxylate species as tridentate ligands, one piperazinediium as counter ion, and eight-uncoordinated water molecules in the asymmetric unit. In both structures each M(IV) is coordinated in a distorted tricapped trigonal prism geometry by three nitrogen and six oxygen atoms of carboxylate groups of three (pydc)²⁻ fragments. In the crystal structures of 1, 2 and 3, extensive O–H···O, N–H···O and C–H···O hydrogen bonds as well as electrostatic forces, C–H···π, C–O···π and π–π stacking play important roles in stabilizing structures. The geometrical parameters of the [M(pydc)₃]²⁻ anionic complexes, where M = Ce(IV), Zr(IV) have been optimized with the B3LYP method of density functional theory (DFT) and ab initio Hartree–Fock (HF) methods for comparison. In addition, we have studied the structures of (pydc)²⁻ anion and its mono and doubly protonated forms, (pydcH)⁻ and pydcH₂. The electronic properties of the anionic complexes and ligands have been investigated based on the natural bond orbital (NBO) analysis at the B3LYP method which verifies that the synergistic effect has been occurred in the title complexes. In solution study of 2, the stoichiometry and stability constant of complexation of pipz, pydc, pydc–pipz proton transfer system and Zr(IV) ion in aqueous solution were investigated by potentiometric method.     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

An efficient and green synthesis of phthalide-fused pyrazole and pyrimidine derivatives

An efficient and green method for the synthesis of phthalide [isobenzofuran-1(3H)-one] fused pyrazoles via the catalyst-free condensation reaction of 2-formylbenzoic acid, hydrazine hydrate, and acetylenic esters in water is reported. Reaction of 2-formylbenzoic acid with 6-amino-uracils or cyclic 1,3-diketones resulted in the formation of phthalide-fused pyrimidine or cyclic 1,3-diketone derivatives.     

One‐Pot Synthesis of Functionalized 3‐Aryl‐1‐phenyl‐1H‐pyrazoles from Hydrazonoyl Chlorides and Acetylenic Esters in the Presence of Ph3P

The zwitterionic 1 : 1 intermediates generated by addition of Ph₃P to acetylenic esters is trapped by 1‐[(aryl)chloromethylene]‐2‐phenylhydrazines (=N‐phenylarenecarbohydrazonoyl chlorides) to yield functionalized 3‐aryl‐1‐phenyl‐1H‐pyrazoles in good yields.     

Density and viscosity of pyridinium-based ionic liquids and their binary mixtures with water at several temperatures

Densities and viscosities of two pyridinium-based ionic liquids, 1-butylpyridinium tetrafluoroborate [BuPy][BF₄] and 1-octylpyridinium tetrafluoroborate [OcPy][BF₄], and their binaries with water at atmospheric pressure and temperatures from (283.15 to 348.15) K were determined. The densities and viscosities of pure ionic liquids were correlated successfully by empirical equations. The Vogel–Fulcher–Tammann equations can fit the experimental viscosities for pure and binary of both IL systems. Excess molar volume and viscosity deviation were calculated for the binaries. The excess molar volumes have positive deviation from ideal solution while the viscosity deviations have negative values.     

Development of deep eutectic solvent–based microwave-assisted extraction combined with temperature controlled ionic liquid–based liquid phase microextraction for extraction of aflatoxins from cheese samples

In this study, for the first time, a deep eutectic solvent-based microwave-assisted extraction was combined with ionic liquid–based temperature controlled liquid phase microextraction for the extraction of several aflatoxins from cheese samples. Briefly, the analytes are extracted from cheese sample (3 g) into a mixture of 1.5 mL choline chloride:ethylene glycol deep eutectic solvent and 3.5 mL deionized water by exposing to microwave irradiations for 60 s at 180 W. The liquid phase was taken and mixed with 55 μL 1-hexyl-3-methylimidazolium hexafluorophosphate. By cooling the solution in the refrigerator centrifuge, a turbid state was obtained and the analytes were extracted into the ionic liquid droplets. The analytes were determined by high-performance liquid chromatography equipped with fluorescence detector. Low limits of detection (9–23 ng kg^–1) and quantification (30–77 ng kg^–1), high extraction recovery (66%–83%), acceptable enrichment factor (40–50), and good precision (relative standard deviations ≤ 5.2%) were obtained using the offered approach. These results reveal the high extraction capability of the method for determination of aflatoxins in the cheese samples. In this method, there was no need for organic solvents and it can be considered as green extraction method.