Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(═O)

Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C(?)═O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical +O2 association reaction are reported along with reaction paths and barriers. Enthalpies, ΔfH298(0), are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C(?)═O radical with O2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol(-1) internal energy; this is significantly more energy than the 21 kcal mol(-1) involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products.     

Activation of propane C–H and C–C bonds by a diplatinum cluster: potential energy surfaces and reaction mechanisms

The activation mechanism of C₃H₈ catalyzed by the homonuclear bimetallic Pt₂ cluster has been detailedly explored on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The C–H bond cleavage channel (dehydrogenation and the release of propylene) is kinetically predominant, whereas the C–C bond cleavage channel (demethanation and the release of ethane) should be ruled out. Furthermore, the release of propylene channel is kinetically favorable, while the dehydrogenation channel is thermodynamically preferable. Besides, both the C–H cleavage intermediate (Pt₂H₂C₃H₆b) and the C–C cleavage intermediates (CH₃HPt₂CHCH₃ and CH₃PtPtHC₂H₄) are thermodynamically preferred. The C–H cleavage intermediate (Pt₂H₂C₃H₆b) is kinetically favored, while the C–C cleavage intermediates (CH₃HPt₂CHCH₃ and CH₃PtPtHC₂H₄) are kinetically hindered. The homonuclear bimetallic Pt₂ cluster toward propane exhibits higher reactivity than the Pt atom, which is in good agreement with the experimental observation.     

Ni–Mo2C supported on alumina as a substitute for Ni–Mo reduced catalysts supported on alumina material for dry reforming of methane

In this study, alumina-supported NiMo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H₂/CH₄) and a reduced NiMo catalyst. It was shown that the passivated alumina-supported NiMo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction.     

Synthesis of a uranium(VI)-carbene: reductive formation of uranyl(V)-methanides, oxidative preparation of a [R2C═U═O]2+ analogue of the [O═U═O]2+ uranyl ion (R = Ph2PNSiMe3), and comparison of the nature of U(IV)═C, U(V)═C, and U(VI)═C double bonds

We report attempts to prepare uranyl(VI)- and uranium(VI) carbenes utilizing deprotonation and oxidation strategies. Treatment of the uranyl(VI)-methanide complex [(BIPMH)UO(2)Cl(THF)] [1, BIPMH = HC(PPh(2)NSiMe(3))(2)] with benzyl-sodium did not afford a uranyl(VI)-carbene via deprotonation. Instead, one-electron reduction and isolation of di- and trinuclear [UO(2)(BIPMH)(μ-Cl)UO(μ-O){BIPMH}] (2) and [UO(μ-O)(BIPMH)(μ(3)-Cl){UO(μ-O)(BIPMH)}(2)] (3), respectively, with concomitant elimination of dibenzyl, was observed. Complexes 2 and 3 represent the first examples of organometallic uranyl(V), and 3 is notable for exhibiting rare cation-cation interactions between uranyl(VI) and uranyl(V) groups. In contrast, two-electron oxidation of the uranium(IV)-carbene [(BIPM)UCl(3)Li(THF)(2)] (4) by 4-morpholine N-oxide afforded the first uranium(VI)-carbene [(BIPM)UOCl(2)] (6). Complex 6 exhibits a trans-CUO linkage that represents a [R(2)C═U═O](2+) analogue of the uranyl ion. Notably, treatment of 4 with other oxidants such as Me(3)NO, C(5)H(5)NO, and TEMPO afforded 1 as the only isolable product. Computational studies of 4, the uranium(V)-carbene [(BIPM)UCl(2)I] (5), and 6 reveal polarized covalent U═C double bonds in each case whose nature is significantly affected by the oxidation state of uranium. Natural Bond Order analyses indicate that upon oxidation from uranium(IV) to (V) to (VI) the uranium contribution to the U═C σ-bond can increase from ca. 18 to 32% and within this component the orbital composition is dominated by 5f character. For the corresponding U═C π-components, the uranium contribution increases from ca. 18 to 26% but then decreases to ca. 24% and is again dominated by 5f contributions. The calculations suggest that as a function of increasing oxidation state of uranium the radial contraction of the valence 5f and 6d orbitals of uranium may outweigh the increased polarizing power of uranium in 6 compared to 5.     

Synthesis of a flavonoid fluorescent probe for the detection of sulfur dioxide derivatives and cell imagingEI北大核心CSCD

A novel fluorescent probe HMQC was synthesized for HSOf detection by coupling flavonoid derivatives with 3-quinoline salt. In PBS buffer solution, the probe showed high selectivity, good sensitivity (58 nmol/L) and rapid response (150 s) for the detection of HSO3−. The possible sensing mechanism of the probe was discussed by nuclear magnetic hydrogen spectroscopy, mass spectrometry and theoretical calculation, indicating that the addition reaction between HSO3− and the C=C bond of the probe led to the fluorescence enhancement. The probe HMQC could be used for the detection of HSO3− in living cells, making it to be a promising tool for delecting HSO3−. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Density functional theory study of the cycloaddition reaction of furan derivatives with masked o-benzoquinones. Does the furan act as a dienophile in the cycloaddition reaction?

The molecular mechanism for the cycloaddition reaction between 2-methylfuran and a masked o-benzoquinone has been characterized using quantum mechanical calculations at the B3LYP/6-31G theory level. An analysis of the results on the reaction pathway shows that the reaction takes place along a polar stepwise mechanism. The first and rate-determining step corresponds to the nucleophilic attack of the furan ring on the doubly conjugated position of the 2,4-dienone system present at the masked o-benzoquinone to give a zwitterionic intermediate. Closure of this intermediate affords the formally [2 + 4] cycloadduct. For the second step two reactive channels have been characterized corresponding to the formation of the formally [2 + 4] and [4 + 2] cycloadducts. Analysis of the energetic results indicates that while the first is the meta regiocontrolling and endo stereocontrolling step, the second one is responsible for the formation of the unexpected formally [2 + 4] cycloadduct. The global and local electrophilicity/nucleophilicity power of the reactants and intermediate have been evaluated to rationalize these results. Density functional theory analysis for these cycloadditions is in complete agreement with the experimental outcome, explaining the reactivity and selectivity of the formation of the formally [2 + 4] cycloadducts.     

Amides as surrogates of aldehydes for C–C bond formation:amide-based direct Knoevenagel-type condensation reaction and related reactions

Aldehydes are perhaps the most versatile compounds that enable many C–C bond forming reactions, which are not amenable for other subclasses of carbonyl compounds. We report the first use of amides as surrogates of aldehydes for C–C bond formation,namely, the direct Knoevenagel-type condensation based on amides. The one-pot method consists of controlled reduction of an amide with LDBIPA [Li Al H(i Bu)2(Oi Pr)], Lewis acid-mediated release of a reactive iminium ion intermediate, nucleophilic addition, and in situ elimination of amine. The reaction shows good functional group tolerance. We also demonstrated that the Schwartz reagent could be used as an alternative of LDBIPA. The employment of nitromethane and a silyl enol ether as the nucleophiles opens an avenue for the unprecedented amide-based nitro-aldol condensation reaction and aldol condensation reaction, respectively.     

Ring-closing metathesis as a new strategy for the C–C coupling of monosaccharide derivatives via silicon tethering

Suitable carbohydrate-derived terminal olefins have been coupled by ring-closing metathesis reaction following a silicon tethering strategy, generating very long contiguous chains of carbon atoms each equipped with specific stereochemistry and functionality.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Hydrogen fluoride adsorption and reaction on the α-Al2O3(0001) surface: a density functional theory study

The adsorption and reaction behaviors of HF on the α-Al(2)O(3)(0001) surface are systematically investigated using density functional theory method. By increasing the number of HF molecules in a p(2 × 1) α-Al(2)O(3)(0001) slab, we find that HF is chemically dissociated at low coverage; while both physical and dissociative adsorption occurs at a 3/2 monolayer (ML) coverage. At the same coverage (1.0 ML), diverse configurations of the dissociated HF are obtained in the p(2 × 1) model; while only one is observed in the p(1 × 1) slab due to its smaller surface area compared with the former one. Preliminary fluorination reaction study suggests that the total energy of two dissociated HF in the p(2 × 1) slab increases by 1.00 and 0.72 eV for the formation and desorption of water intermediate, respectively. The coadsorption behaviors of HF and H(2)O indicate that the pre-adsorbed water is unfavorable for the fluorination of Al(2)O(3), which is well consistent with the experimental results. The calculated density of states show that the peak of σ(H-F) disappears, while the peaks of σ(H-O) and σ(Al-F) are observed at -8.4 and -5 to -3 eV for the dissociated HF. Charge density difference analysis indicates that the dissociated F atom attracts electrons, while no obvious changes on electrons are observed for the surface Al atoms.     

The CC double bond of a bidentate carbene-alkene complex of tungsten as an internal NMR probe for the coordination of Lewis acids

The rate of polymerization of alkynes induced by tungsten complexes containing a coordinated CC double bond can be considerably enhanced by Lewis acids such as AIR₃. The interaction of the two catalyst components studied by means of NMR spectroscopy, leads to a weakening of the bond between the metal and the double bond.     

Formation of the aggregates of actinocin derivatives containing 4′-benzo-15-crown-5 radicals in amide groups and their interaction with a DNA molecule

Methods of spectrophotometry, spectropolarimetry, and viscometry are used to study the self-organization in the solution of crown-containing actinocin derivative (I) exhibiting antitumor activity and the interaction of the formed aggregates with a DNA molecule. The presence of the 4′-benzo-15-crown-5 radical in the structure of the studied compound determines the observed differences in its complexation with Na⁺ and K⁺ ions. The process of aggregation in the presence of K⁺ ions is accompanied by a shift of the long-wave band in the absorption spectrum to short-wave (the formation of H type aggregates) or long-wave (the formation of J type aggregates) regions depending on the K⁺ ion concentration in the solution. In the presence of Na⁺ ions, regardless of their concentration in the solution, J type aggregates form. A scheme of complex formation and their mutual transformations with changes in the ionic composition of the medium is proposed. A study of the interaction of this compound with DNA shows that in the presence of K⁺ ions it binds to the DNA molecule in the form of monomers and/or dimers without producing large supramolecular aggregates. The H and J structures formed in K⁺-containing solutions of compound I are broken in the interaction with DNA. If a solution of compound I is added to a DNA solution containing Na⁺ ions, the J type aggregates are formed directly on the surface of the DNA molecule. At the same type, the J structures originally formed in the Na⁺-containing solution of compound I practically do not interact with DNA. A study of this system shows that the introduction of the crown group in the compound molecule with a heterocyclic chromophore provides the opportunity to affect its affinity and binding to the DNA molecule by means of the ionic composition of the medium.     

Semiclassical calculation of the reaction probability for the process C + O → CO on a Pt(111) surface

The formation of CO on a Pt(111) surface is studied using a semiclassical approach. The reaction probability is calculated as a function of kinetic energy of the carbon atom and initial oxygen position on the surface.     

Bornane-2,10-sultam: a highly efficient chiral controller and mechanistic probe for the intermolecular Pauson–Khand reaction

The origin of the essentially complete diastereoselectivity observed in the intermolecular Pauson–Khand reactions of N-(2-alkynoyl)bornane-2,10-sultam derivatives has been studied by a combination of experimental and theoretical techniques. PM3(tm) calculations show that the corresponding dicobalthexacarbonyl complexes have only two stable conformations that are geometrically very similar. The CD spectra of these complexes are in accordance with these calculations. Finally, a PM3(tm)//DFT study of the putative intermediates in the Pauson–Khand cycloaddition of complex 5b with norbornadiene shows that an oxygen atom of the sultam moiety of the auxiliary can selectively chelate one of the cobalt atoms of the initially formed alkyne–dicobaltpentacarbonyl complex, and that the coordination of the olefin to the same cobalt in a well-defined orientation is also the energetically preferred option. This chelation effect leads to an extremely efficient chirality transfer to the C₂Co₂ tetrahedral core of the alkyne–dicobaltcarbonyl complex and completely determines the diastereoselectivity of the process.     

Design and synthesis of á, á-trehalose derivatives bearing guanidino groups as inhibitors for the Tat Protein-TAR RNA interaction of HIV-1

Replication of human immunodeficiency virus type 1 (HIV-1) requires specific interactions of Tat protein with the transactivation responsive region (TAR) RNA. Disruption of Tat-TAR RNA interaction could inhibit HIV-1 replication. Here four target compounds were designed and synthesized to bind to TAR RNA for blocking the interaction of Tat-TAR RNA. The core molecule 6,6'-diamino-6,6' -dideoxy-α,α-trehalose was obtained from selective bromination of α,α-trehalose at C-6,6', fo…