Radical cations of 1,4-dialkoxybenzenes and alkyl 1,4-dialkoxybenzenes generated through one-electron oxidation by perfluorodiacyl peroxides

Radical cations of 1,4-dialkoxybenzenes 1 and 2 and alkyl 1,4-dialkoxybenzenes 3–9 generated in oxidation of the parent donors by perfluorodi[1-(2-fluorosulfonyl)ethoxy]propionyl peroxide 10 at −40°C and pentafluorobenzoyl peroxide 11 at 15°C were observed by ESR. Radical cation 6^+˙, generated in other oxidation systems, i.e., Ce(SO₄)₂/THF, NH₄/OAc and (NH₄)₂S₂O₈/HOAc, has also been investigated. Based on ESR observation and products analysis, an electron-transfer mechanism of the oxidation reaction is proposed and the influencing factors on hyperfine splitting constants of the radical cations are discussed.     

Photooxygenations of 1-naphthols: an environmentally friendly access to 1,4-naphthoquinones

Dye sensitized photooxygenations of 1-naphthols were investigated with soluble and solid-supported sensitizers and moderate to excellent yields of the corresponding 1,4-naphthoquinones were achieved in relatively short irradiation times. The mild and environmentally friendly reaction conditions made this application particularly attractive for ‘Green Photochemistry’. Consequently, the photooxygenation of 1,5-dihydroxynaphthalene was studied with non-concentrated and moderately concentrated sunlight and 5-hydroxy-1,4-naphthoquinone (Juglone) was obtained in yields up to 71%.     

F‐bridged Anions of Bromine and Gold: Predictions of Unexpected Behavior

The significant similarity between MF₃, MF₄^–, and M₂F₇^– (M = Au, Br) is studied using quantum chemical methods. It is expected that compounds containing Au₃F₁₀^– anions are likely to be stable. A theoretical background for the ongoing attempts of their synthesis is provided by calculations on the stabilities and molecular structures of various bromine and gold anions with the general composition of M_nF_3n+1^– (n = 1, 2, 3, 4). The anions show unexpected differences and peculiarities in their energetically preferable molecular structures. Different chain‐like structures are predicted as the global minima for the hypothetical Au₃F₁₀^– and Br₄F₁₃^– anions.     

p-Benzyne

A noble gas matrix at low temperature was used to investigate the photochemical behavior of diacetyl terephthaloyl diperoxide and dipropionyl terephthaloyl diperoxide as well as 1,4-diiodobenzene. All three photoreactions formed small quantities of a compound with IR absorption bands at 725 and 980 cm⁻¹, which disappeared when the matrix was annealed. These bands correspond to the most intense of the calculated bands (B3LYP) for 1,4-didehydrobenzene (p-benzyne) ( 1 ). That decomposition of the peroxides in fact leads to 1 is confirmed by vapor-phase pyrolysis experiments in which (Z)- 2 was obtained in high yield.     

Photoacylations of 2-substituted 1,4-naphthoquinones: a concise access to biologically active quinonoid compounds

Photochemical acylations of 2-substituted-1,4-naphthoquinones with various aldehydes furnished acylated hydroquinones and acylated quinones in moderate to good combined yields. All reactions are easily performed and open a rapid access to biologically active compounds. For the 2-methyl-1,4-naphthoquinone/butyraldehyde pair, a novel tri-keto compound has been additionally isolated.     

Fragmentation studies of synthetic 2-acylamino-1,4-naphthoquinones by electrospray ionization mass spectrometry

We report here the fragmentation mechanism for five 2-acylamino-1,4-naphthoquinone derivatives using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Analyses were performed on a low-resolution, triple-quadrupole mass spectrometer. Fragmentation pathways for protonated molecular derivatives 2-acylamino-1,4-naphthoquinone [M+H]+ are proposed on the basis of theoretical calculations. There is evidence that the nitrogen atom is the protonation site, based on the nucleophilic atomic indices.     

Bis(trifluoromethyl)dicarbonate, CF3OC(O)OC(O)OCF3

The synthesis of the new compound, bis(trifluoromethyl)dicarbonate, CF₃OC(O)OC(O)OCF₃, is carried out by reduction of bis(trifluoromethyl)trioxidicarbonate with excess of CO at 0 °C. The product is characterized by IR, Raman, ¹³C and ¹⁹F NMR spectroscopy and its properties are compared with those of the other members of the series CF₃OC(O)O_xC(O)OCF₃, x = 0-3. Single crystals are grown at −25 °C and the X-ray diffraction analysis shows the packing of syn-syn rotamers exhibiting C₂ symmetry. DFT calculations predict this rotamer as the most stable one and also structural and vibrational data are predicted reasonably well.     

1,4-Addition of a Terminal Phosphinidene Complex to [5]Metacyclophane

Three novel aspects emerge for the reaction of [5]metacyclophane ( 1 ) with the (intermediate) phenylphosphinidene complex 2 to give the 7-phosphanorbornadiene 3 . It is the first 1,4-addition of a phosphinidene complex to an unsaturated system, the first addition of a phosphinidene complex to a benzene ring, and the first [4+1] cycloaddition to an aromatic compound.     

Studies on the chemistry of 2-(2-oxo-3-phenylpropyl)-benzaldehydes: novel total synthesis of 3-phenylnaphthalen-2-ols and 2-hydroxy-3-phenyl-1,4-naphthoquinones

We describe the first studies on the chemistry of 2-(2-oxo-3-phenylpropyl)benzaldehydes, which were converted into 3-benzylisochromen-1-ones via the corresponding 2-(2-oxo-3-phenylpropyl)benzoic acid. The 2-(2-oxo-3-phenylpropyl)benzaldehydes proved to be convenient starting materials for the synthesis of 3-phenyl-2-naphthols. Oxidation of the latter compounds resulted in a novel, efficient synthesis of 3-phenyl-1,2-naphthoquinones, which were efficiently transformed into 2-hydroxy-3-phenyl-1,4-naphthoquinones.     

Enantioselective Desymmetrization of 1,4-Dihydropyridines by Oxidative NHC Catalysis

The unprecedented desymmetrization of prochiral dialdehydes catalyzed by N-heterocyclic carbenes under oxidative conditions was applied to the highly enantioselective synthesis of 1,4-dihydropyridines (DHPs) starting from 3,5-dicarbaldehyde substrates. Synthetic elaboration of the resulting 5-formyl-1,4-DHP-3-carboxylates allowed for access to the class of pharmaceutically relevant 1,4-DHP-3,5-dicarboxylates (Hantzsch esters). DFT calculations suggested that the enantioselectivity of the process is determined by the transition state involving the oxidation of the Breslow intermediate by the external quinone oxidant.     

NMR Properties of Polylithiated C60

Endohedral, ¹³C, ⁷Li, and nucleus‐independent (NICS) chemical shifts are reported for selected Li_nC₆₀ isomers (n = 6, 12, 18) at the GIAO (gauge‐including atomic orbitals)‐SCF/DZP//BP86/3–21G level. Li₆C₆₀ closely resembles C₆₀^6– in terms of NMR criteria for aromaticity, as evidenced by an exceptionally high endohedral shielding. In contrast, nonaromaticity is indicated for Li₁₂C₆₀, based on a positive endohedral chemical shift. NICS and δ(endo) values very similar to those of Li₁₂C₆₀ are obtained for Li₁₈C₆₀. According to population analysis, indeed the same number of electrons are transferred to the fullerene cage in both cases. Endohedral chemical shifts, accessible via ³He NMR of the corresponding endohedral helium compounds, could thus be a valuable indicator for the extent of reduction of the C₆₀ molecule. Energetic estimates suggest that in the bulk, Li₁₂C₆₀ should be unstable with respect to decomposition into Li₆C₆₀ and lithium metal.     

Density Functional Theory Calculations of the Barrier to Atropisomerism of a Dibenzo[d,f][1, 3, 2]dioxaphosphepin Moiety: a Tool for Rational Ligand Design

Density functional theory calculations yield reasonable values for the barrier to atropisomerism in a dibenzo[d, f][1, 3, 2]dioxaphosphepin moiety of diphosphite ligands and thus provide an energetic criterion for falsification of hypothetical stable stereoisomers in rational ligand design.     

Computational approaches to design a molecular imprinted polymer for high selective extraction of 3,4-methylenedioxymethamphetamine from plasma

In this work, a molecular imprinted polymer (MIP) as a novel selective sorbent for extraction of 3,4-methylenedioxymethamphetamine (MDMA) from plasma samples was prepared. For selecting a more suitable monomer and polymerization solvent a methodology based on density functional theory calculations was developed. This computational design is based on the comparison of stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of polymerization solvent was studied using of polarizable continuum model (PCM). The computational results revealed that the best suitable monomer and polymerization solvent for preparation of MIP is methacrylic acid (MAA) and chloroform, respectively. Also, another MIP with methacrylic acid (MAA) as monomer in acetonitrile was prepared to evaluate the validity of polarizable continuum model for selection of polymerization solvent. The performance of each polymer was evaluated by using Langmuir-Freundlich (LF) isotherm. As it is expected, the best results were obtained for the MIP which was prepared in chloroform. This MIP was used as a selective sorbent in solid-phase extraction coupled with high performance liquid chromatography-ultraviolet detector (MISPE-HPLC-UV) for rapid screening of MDMA in human plasma. For the proposed MISPE-HPLC-UV method, the linearity between responses (peak areas) and concentrations was found over the range of 3.6-11500 ng mL(-1) with a linear regression coefficient of 0.998. The limit of detection (LOD) and quantification (LOQ) in plasma were 1.0 and 3.3 ng mL(-1), respectively. The %RSD (n=5) data for five plasma samples containing 15, 25, 50, and 100 ng mL(-1) of MDMA were 1.02, 1.12, 2.05, 2.54, respectively.     

Hydrogen Bonded Complexes of Acetylacetone and Methanol: HF and DFT level Study

Summary. Several possible hydrogen-bonded complexes between the tautomeric forms of acetylacetone and methanol were studied by ab initio methods using 6-311G** and D95** basis functions at the HF and DFT (B3LYP) levels of theory. The calculations were carried out for isolated molecules and solvent assisted complexes by means of the isodensity polarized model (IPCM). The theoretical frequencies were compared with the experimental IR spectrum of an equimolar mixture of acetylacetone and methanol. It was proved that the most stable H-bonded complex acetylacetone–methanol is formed between O-bonded methanol- and the enol molecule.     

F＋Cl2->ClF＋Cl和Cl′F＋Cl->Cl′＋ClF的反应机理

用密度泛函理论(DFT)B3LYP方法,取6 311G基组,计算研究了F＋Cl2ClF＋Cl的反应机理.求得1个线形和2个三角形过渡态,反应能垒分别为1.24、46.37和105.09kJ•mol－1;同时发现F以∠FClCl为10～20°（或 120～160°）进攻Cl2时,反应无能垒.此外,求得对称反应Cl′F＋ClCl′＋ClF的能垒为40.57 kJ•mol－1的1个过渡态.     

Quinoline-based highly selective and sensitive fluorescent probe specific for Cd2+ detection in mixed aqueous media

Quinoline-based fluorescent probe as a recognition unit was designed and synthesized in this study. The probe R1 displayed excellent selectivity and sensitivity for cadmium ions (Cd²⁺) over a wide range of metal ions in acetonitrile-water (MeCN-H₂O) mixed solution. In order to better understand the recognition mechanism between probe and Cd²⁺, the density functional theory calculations were performed. Finally, the colorimetric experiment result was observed and conveniently monitored by the naked eye, and a visual detection limit of 4 × 10^?6 mol L^?1 was achieved. These experimental results indicated the promising potential of the probe to detect Cd²⁺ in biological system. Furthermore, the probe R1 was successfully used for the highly sensitive detection of Cd²⁺ in living cells.     

Barium Peroxide: a Simple Test Case for First‐Principles Investigations on the Temperature Dependence of Solid‐State Vibrational Frequencies

The vibrational properties of barium peroxide, BaO₂, were investigated by phonon calculations based on density‐functional theory and the ab initio force‐constant method. In order to reproduce the correct wavenumber of the peroxide vibration at finite temperatures, its volume dependence together with the calculated volume expansion was taken into account. Using this approximation we found a quantitative agreement of the calculated value with experimental data observed by Raman spectroscopy.     

Synthesis of anticonvulsant sulfamides. Theoretical study of the related mechanism

A theoretical study of the mechanisms associated with the synthesis of anticonvulsant symmetric N,N-substituted sulfamides is presented. Two possible synthetic routes are compared, which mainly differ in the use of pyridine as a nucleophilic agent in the reaction mechanism. Geometry optimization techniques and transition-state detection at the B3LYP/6-31G** level, modeling the solvent by means of an isodensity polarizable continuum approach, allow the most suitable method for the experimental process to be discerned.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)