Preparation, 13C NMR and IGLO/DFT studies of trifluoromethyl substituted allyl cations

α-Trifluoromethyl substituted allyl cations 3 and 4 have been prepared by ionizing their corresponding alcohols with SbF₅ in SO₂CIF at low temperatures. The barriers to rotation around the C1–C2 bond of the both cations were determined to be about 9 kcal/mol. The unusually low barriers as compared with their methyl analogues are rationalized by the unsymmetrical nature of the cations. CF₃-substituted cyclohexenyl cations 8 and 10 were also prepared and characterized by ¹³C NMR spectroscopy. Density functional theory (DFT) calculations were performed to investigate geometries and charge densities of tifluoromethyl substituted allyl cations. ¹³C NMR chemical shifts of the cations were also calculated by IGLO method and compared with the experimental results.     

Synthesis and NMR elucidation of novel amino acid cavitand derivatives

The synthesis of seven novel protected amino acid cavitands is reported. All have four pendant n-undecyl chains and ‘headgroups’ connected by a two-carbon spacer at four positions on the aromatic rings. The amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine and lysine. The structures of the compounds were elucidated using one- and two-dimensional NMR techniques, which verified that all tetra-substituted cavitands have symmetrical C_4v conformation. This is the first example of a complete study for amino acid cavitand derivatives.     

Synthesis and 13C NMR of (trifluoromethyl)hydroxypyrazoles

Reaction of ethyl 4,4,4-trifluoroacetoacetate with methylhydrazine produced not only the previously reported 5-hydroxy-3-(trifluoromethyl)pyrazole 1 but also its unknown isomer the 3-hydroxy-5-(trifluoromethyl)pyrazole 4 . The structure assignments are established based on ¹³C nmr spectra. Compound 1 was converted to 5-chloro-3-(trifluoromethyl)pyrazolecarboxylic acid 3 in two steps.     

Synthesis and structure elucidation of five new conjugates of oleanolic acid derivatives and chalcones using 1D and 2D NMR spectroscopy

Five new conjugates of oleanolic acid derivatives and chalcones have been designed and synthesized. The structure elucidation of these conjugates was accomplished by using extensive 1D (¹H, ¹³C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC); and α‐glucosidase inhibitory activity is reported for these conjugates. Compound 2b (IC₅₀ = 47.5 µm ) displayed much stronger activity than oleanolic acid and acarbose. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and structural elucidation of a phthalide analog using NMR analysis and DFT calculations

Phtalides are secondary metabolites found in several fungi with a wide range of biological activities. A novel phthalide analog was synthesized by Diels–Alder reaction between cyclopentadiene and 3,4-dichlorofuran-2(5H)-one. Quantum mechanical calculations were used in conjunction with the spectrometric methods to determine the structure of the title compound. The calculated NMR chemical shifts for eight candidate pairs of enantiomers were compared with the experimental NMR chemical shifts applying the DP4 probability and mean absolute errors methodology. DP4 analysis using ¹H and ¹³C NMR chemical shifts without assignment of the signals presented 100% probability for the correct candidate structure 3d , proving the consistency of the method even without spectra interpretation. Results from theoretical calculation and NMR spectra interpretation were in agreement to the structure of rac-(3aR,4S,4aS,5R,8S,8aR,9R,9aS)-3a,9a-dichloro-3a,4,4a,5,8,8a,9,9a-octahydro-4,9:5,8-dimethanonaphtho[2,3-c]furan-1(3H)-one.     

Novel tricarbonyl rhenium complexes of 5,8-quinolinedione derivatives - Synthesis, spectroscopic characterisation, X-ray structure and DFT calculations

The molecular structure of 7-acetamido-2-methyl-quinoline-5,8-dione has been determined and the reactivity of 7-acetamido-2-methyl-quinoline-5,8-dione (1) and 6-acetamido-2-methyl-quinoline-5,8-dione (2) towards Re(CO)₅Cl has been examined. Two novel tricarbonyl rhenium complexes, fac-[Re(CO)₃(7-acetamido-2-methyl-quinoline-5,8-dione)Cl]·CHCl₃ (3·CHCl₃) and fac-[Re(CO)₃(6-acetamido-2-methyl-quinoline-5,8-dione)Cl]₂·CHCl₃ (4·CHCl₃), have been synthesized and characterized spectroscopically and structurally. The electronic spectrum of 3 was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Synthesis, NMR and X-ray structure analysis of macrolide aglycons

Macrolide aglycons (E)-9-hydroxyimino-6-O-methylerythronolide A (4), 9a-aza-9-deoxo-9,9-dihydro-9a,11-O-dimethyl-9a-homoerythronolide A (5) and 9a-aza-9-deoxo-9,9-dihydro-9a-homoerythronolide A (6) were prepared by multistep syntheses. A conformational study of these new macrolide aglycons was performed using single crystal X-ray crystallography to gain information about the solid state, while a combination of NMR spectroscopy and molecular modelling was employed to study the solution structures. The crystal structures were found to be stabilised by a complex network of hydrogen bonds and van der Waals interactions. To some extent, the same building motif of infinite molecular chains held together by O?CH···O hydrogen bonds was present in the crystal structure of all three compounds. Thorough analysis and comparison of the obtained solid state structures with their solution counterparts showed no significant differences between them, confirming the constrained flexibility of the macrocyclic ring. Moreover, in all three compounds, in both solution and solid state, the macrolactone ring adopts energetically more favoured folded-out conformations.     

Synthesis and structure elucidation of new cytotoxic azathioxanthones

A series of new cytotoxic azathioxanthones 7a-h was synthesized and characterized by their spectral data.     

Synthesis and NMR elucidation of pentacyclo-undecane diamine derivatives as potential anti-tuberculosis drugs

The complete structural elucidation of six novel pentacycloundecane (PCU) derivatives is reported. The target molecules are potential anti-tuberculosis agents. The addition of side arms to the PCU cage skeleton at position C-8/C-11 results in major overlapping of the methine resonances of the ¹H NMR spectrum. The use of 2D NMR techniques proved to be a very useful tool in overcoming the difficulties encountered in the elucidation of cage compounds using ¹H and ¹³C spectra only. All compounds reported are meso compounds thereby simplifying the complexity of the NMR spectra. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural elucidation of a new delta2-pyrazoline derivatives using 1H and 13C NMR spectroscopy

This paper describes the unequivocal structural elucidation of a new kind of Delta2-pyrazoline derivatives carried out by means of monodimensional 1H and 13C NMR spectroscopies, bidimensional ones such as HMBC and HMQC experiments, and NOEDIFF effects. Conformational analysis of this molecule agrees very well with the experimentally NOEDIFF effects found.     

Synthesis, characterization and DFT calculations of new ethynyl-bridged C60 derivatives

A new series of soluble C₆₀ derivatives for organic electronic application has been synthesized by ethynylation reaction using different electron-donating and electron-withdrawing groups of varying length.     

H and C NMR spectroscopic structural elucidation of new decarboxylated betacyanins

Novel mono- and bi-decarboxylated betacyanins were generated by thermal decarboxylation of betacyanins of purple pitaya (Hylocereus polyrhizus) fruits and were identified by ¹H and ¹³C NMR spectroscopy.     

Synthesis and X-ray structure of C2-C84(22)(CF3)6

1. Download : Download full-size image

     

Synthesis,experimental and DFT studies on crystal structure,FT-IR, 1H,and 13C NMR spectra,and evaluation of aromaticity of three derivatives of xanthens

Several derivatives of xanthenes are prepared by the condensation of aldehydes and dimedone in H₂O in the presence of a catalytic amount of trichlorotriazine. The crystalline products were characterized by FTIR, ¹H, and ¹³C NMR spectra. Density Functional Theory (DFT) calculations on the B3LYP level were used to optimize the geometry and calculate the crystal structure, FTIR, ¹H NMR and ¹³C NMR spectra of the selected synthesized compounds. We found that the values of FTIR, ¹H, and ¹³C NMR spectra obtained by the B3LYP method are in accordance with experimental data. The calculated NICS indicate that the six-membered rings in xanthenes are essentially homoaromatic.     

Synthesis and NMR elucidation of novel penta-cycloundecane amine derivatives as potential antituberculosis agents

The synthesis and NMR elucidation of five novel penta-cycloundecane amine derivatives are reported. These compounds are potential antituberculosis agents. The (1)H and (13)C spectra showed major overlapping of methine signals of the cage skeleton making it extremely difficult to elucidate these compounds. The overlapping occurs as a result of the additions made to the carbonyl carbon (C-8/C-11) of the cage. The two-dimensional NMR technique proved to be a useful tool in overcoming this problem. All compounds reported are meso compounds thereby not only simplifying the NMR structure elucidation, but also making it indeed possible.     

Structure elucidation and NMR assignment of two new eudesmane derivatives from Merremia yunnanensis

Two new eudesmane derivatives, 1α,6β,9β-trihydroxy-eudesm-3-ene-1-O-β-d -glucopyranoside ( 1 ) and 1α,6β,9β-trihydroxy-eudesm-3-ene-1-(6-cinnamoyl)-O-β-d -glucopyranoside ( 2 ) were discovered from Merremia yunnanensis. The structures were elucidated by analysis of their spectroscopic data including HR-ESI-MS, 1D, and 2D NMR. It should be noted that this is the first report about structure elucidation and NMR assignment of compounds from M. yunnanensis.     

Preparation and crystal structure of C84(11)Cl20,22, chloro derivatives of a C84 minor isomer

Chlorofullerenes C₈₄(11)Cl₂₀ and C₈₄(11)Cl₂₂ were prepared by chlorination of C₂–C₈₄(11) with VCl₄ at 340–360 °C. An X-ray crystallographic study with the use of synchrotron radiation revealed the chlorination patterns featuring only para additions in C₆Cl₂ hexagons.     

Preparation,structure elucidation,and antioxidant activity of new bis(thiosemicarbazone) derivatives

Schiff-base–bearing new bis(thiosemicarbazone) derivatives were prepared from terephthalaldehyde and various thiosemicarbazides. FT–IR, ¹H NMR, ¹³C NMR, and UV–Vis spectroscopic methods and elemental analysis were used to elucidate the identification of the synthesized molecules. The in vitro antioxidant activity of the synthesized compounds was analysed with the 1,1-diphenyl-2-picryl hydrazyl free-radical–trapping process. The synthesized compounds exhibited lower antioxidant activity than the standard ascorbic acid. IC₅₀ values of the synthesized molecules measured from 3.81 ± 0.01 to 29.05 ± 0.11 μM. Among the synthesized compounds, compound 3 had the best antioxidant activity. Moreover, this study explained the structure–activity relationship of the synthesized molecules with different substituents in radical trapping reactions.     

X-ray crystallographic proof of the isomer D2-C84(5) as trifluoromethylated and chlorinated derivatives, C84(CF3)16, C84Cl20, and C84Cl32

Minor isomer comes forward: Minor isomer C(84)(5) has been captured by high temperature trifluoromethylation with CF(3)I and chlorination with VCl(4). The compounds C(84)(CF(3))(16), C(84)Cl(20), and C(84)(5)Cl(32) were investigated by X-ray crystallography providing the first direct proof of the cage connectivity of D(2)-C(84)(5). The D(2)-C(84)(5)Cl(32) molecule (see figure; C grey, Cl green) contains two flattened, pyrene-like substructures on opposite poles of the cage resulting in its drum-like shape.