Semi-cartesian product of graphs

In this paper, we define a kind of new product graphs with hexagonal inner faces, called semi-cartesian products, so that they directly link with hexagonal system, e.g., the semi-cartesian product of an even cycle and a path is a zigzag polyhex nanotube, a path and an even cycle is an armchair polyhex nanotube, two even cycles is a polyhex nanotorus and two paths is a polyhex lattice. Then we consider the distance in a semi-cartesian product and show two formulas to calculate the distance of two vertices and the sum of all pair of distances. Moreover we illustrate that the applying of the semi-cartesian products would be greatly simplifies the calculation of the distances in the carbon nanotubes and polyhex nanotorus by presenting some examples.     

A theoretical study on the trans-addition intramolecular hydroacylation of 4-alkynals catalyzed by cationic rhodium complexes

The mechanism of the intramolecular hydroacylation reaction of 4-alkynals is studied for a 4-pentynal-[Rh(PH2CH2CH2PH2)]+ model system using MP2 calculations. The endo-cyclization to form a rhodacyclohexenone intermediate is kinetically less favorable than the exo-cyclization to form a rhodacyclopentanone intermediate. The kinetic preference toward the endo-cyclization is found to be enhanced by complexation of donor ligands (H2CO, NCH, and HCCH). The formation of cyclopentenone product proceeds via reductive elimination from one of the two rhodacyclohexenone intermediates, whereas the formation of cyclobutanone product from the two rhodacyclopentanone intermediates requires high activation energy. Addition of an acetylene stabilizes the highly electron-poor rhodacyclopentanone intermediate generated from exo-cyclization and leads to an insertion to give [4 + 2] annulation product, cyclohexenone. The role of a coordinating acetone solvent in the formation of cyclopentenone product is also discussed.     

Anodic behavior of clioquinol at a glassy carbon electrode

Clioquinol is an antifungal, antiprotozoal and an Alzheimer's disease drug with cytotoxic activity toward human cancer cells. The electrochemical behavior of clioquinol and its oxidation product was studied using cyclic, differential pulse and square-wave voltammetry over a wide pH range on a glassy carbon electrode. The results revealed that the oxidation of clioquinol is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism and results in the formation of a main oxidation product, which adsorbs very strongly on the glassy carbon surface. The charge transfer coefficient was calculated as 0.64. The adsorbed oxidation product presented reversible redox behavior, with two electron and two proton transfer. The electrochemical oxidation of clioquinol as a phenolic compound involves the formation of a phenoxy radical which reacts in at least two ways: in one pathway the radical initiates polymerization, the products remaining at the electrode surface, and in the other the radical is oxidized to a quinone-like structure. A mechanism for the oxidation of clioquinol is proposed.     

The general Gaussian product theorem

The Gaussian Product Theorem between two 1s Gaussian Type Orbitals (GTOs) is extended to an arbitrary number of s-type functions, giving a compact formula which permits to express the condensed GTO result. Then, this new formulation is combined with the product of arbitrary GTO Cartesian angular parts, obtaining a finite expansion expressing this product as a multilinear combination of such functions sharing a common center. The combination of both results constitutes the General Gaussian Product Theorem (GGPT), a final compact expression for the product of an arbitrary number of Cartesian GTOs. The notation provides an easy way to express algebraically any general multicenter GTO product expression. It is also shown how by means of Nested Summation Symbols the computational implementation can be easily and elegantly achieved. Computational parallelizable schemes of the GGPT are provided.     

Synthesis of terpene and steroid dimers and trimers having cyclobutadienyl-Co and aromatic tethers

The reaction of natural product derived propargylic alcohols with CpCo(CO)2 produces three new types of natural product hybrids having two or three terpene or steroid fragments. The tether joining the natural product subunits is built during the reaction. Type 1 hybrids have two terpene or steroid moieties joined by a CpCo-cyclobutadiene tether, with the two units disposed in a 1,2-arrangement (9, 14, 22). Type 2 hybrids have a Co-cyclopentadienone tether (10). Type 3 has three units of terpene or steroid joined to a benzene ring (11, 12, 15). An unusual Co-mediated beta-carbon elimination pathway of propargylic alcohols leading to ketones (an unknown process in this chemistry) has been observed.     

Complete quantum control of the population transfer branching ratio between two degenerate target states

A five-level four-pulse phase-sensitive extended stimulated Raman adiabatic passage scheme is proposed to realize complete control of the population transfer branching ratio between two degenerate target states. The control is achieved via a three-node null eigenstate that can be correlated with an arbitrary superposition of the target states. Our results suggest that complete suppression of the yield of one of two degenerate product states, and therefore absolute selectivity in photochemistry, is achievable and predictable, even without studying the properties of the unwanted product state beforehand.     

The products of 5-fluorouridine by the action of the pseudouridine synthase TruB disfavor one mechanism and suggest another

The pseudouridine synthase TruB handles 5-fluorouridine in RNA as a substrate, converting it into two isomeric hydrated products. Unexpectedly, the two products differ not in the hydrated pyrimidine ring but in the pentose ring, which is epimerized to arabinose in the minor product. This inversion of stereochemistry at C2' suggests that pseudouridine generation may proceed by a mechanism involving a glycal intermediate or that the previously proposed mechanism involving an acylal intermediate operates but with an added reaction manifold for 5-fluorouridine versus uridine. The arabino product strongly disfavors a mechanism involving a Michael addition to the pyrimidine ring.     

Six- versus five-membered ring formation in radical cyclizations of 7-bromo-substituted hexahydroindolinones

[reaction: see text] Radical cyclization of N-allyl-7-bromo-3a-methyl-hexahydroindol-2-one affords a six-membered ring product that prevails over the isomeric five-membered compound. The former product is generated through two reaction pathways: (a) 6-endo-trig ring closure and (b) rearrangement of an intermediate methylenecyclopentyl radical obtained by 5-exo-trig cyclization.     

Surface and fluorescence properties of a novel fluorescent surfactant

A novel kind of fluorescent surfactant having 7-hydroxylcoumarin group in the long alkyl chain was synthesized. The critical micelle concentration (CMC), surface tension (γ_cmc) at CMC and absorption, fluorescence properties of this product were determined. From the variations of fluorescence spectra in different solvents, it is observed that the polarity and dielectric constant of the solvents play important roles in the maximum fluorescence intensity and wavelength. Moreover, the surprised exhibition of two fluorescence bands in neutral and alkaline solutions has been attributed to the superexciplex formation of the product molecules. Also, the lower product concentration measuring the fluorescence properties as well as the supposed configuration of hydrogen bond of the product indicate that the larger aggregations cannot exist in alkaline solutions. The superexciplex is a possibility with two or more polar excited molecules together to form an excited state association.     

Photocycloadditions of tetrachloro-1,4-benzoquinone (chloranil) onto cyclobutene and cyclopropene. Expected and unexpected products

Solutions of chloranil (CA) in chlorobenzene were irradiated in the presence of cyclobutene and cyclopropene. Cyclobutene gave rise to two conventional 1 : 2 cycloadducts onto the dichloroethene subunits of CA and an α,β-unsaturated α,γ-dichloro-γ-lactone. Heating of the crude product in methanol converted the lactone into an α,β-unsaturated methyl γ-oxocarboxylate (25% yield) and a large amount of the major 1 : 2 cycloadduct, which contains chlorocyclobutane entities, into a cyclopropylcarbinyl chloride derivative (24% yield). An entirely new product type was the result in the case of cyclopropene. After treatment of the crude product with methanol a tetracyclic acetal containing a cyclopentanone and a dihydropyran subunit was isolated in 36% yield. Apparently, CA had taken up two molecules of cyclopropene. One of the resulting cyclopropane entities must have undergone a rearrangement en route to the final product.     

Reduction of CO2 to CO using low-coordinate iron: formation of a four-coordinate iron dicarbonyl complex and a bridging carbonate complex

A reduced diiron(I) complex reacts with CO(2) to give two iron-containing products. One product has a carbonate bridge, which isomerizes rapidly at -70 degrees C and may be derived from an oxodiiron intermediate. The formation of this product releases free CO, which leads to a four-coordinate iron dicarbonyl complex. This product is the first crystallographically characterized example of a four-coordinate iron dicarbonyl species, a moiety that may be present in the active site of Hmd ("iron-sulfur cluster free") hydrogenase.     

Reaction of Ni2Cp2(mu-CO)2 with the alkylgallium(I) and alkylindium(I) compounds E4[C(SiMe3)3]4 (E = Ga, In). Insertion of E-R groups into the Ni-Ni bond versus replacement of CO by the isolobal E-R ligands

The monomeric fragment In-C(SiMe3)3 was inserted into the Ni-Ni bond of Ni2Cp2(mu-CO)2 upon treatment of the carbonyl complex with the tetraindium(I) compound In4[C(SiMe3)3]4, 1, in a molar ratio of 4 to 1. The product (3) contains an indium atom coordinated to one alkyl substituent and two Ni(Cp)CO groups in a planar coordination sphere. Reaction of the starting compounds in a molar ratio of 2 to 1 led to the replacement of both CO ligands by two InR groups. A compound (4) was formed that is isostructural to the carbonyl nickel complex and has a Ni2 couple bridged by two InR ligands and two terminally coordinated cyclopentadienyl groups. The insertion product was not observed with the gallium derivative Ga4[C(SiMe3)3]4 (2); instead, a nickel gallium complex (5) analogous to 4 containing two bridging GaR ligands was isolated as the only product regardless of the ratio of the starting compounds. On the basis of quantum chemical calculations, we conclude that there is no evidence for an In-In or Ga-Ga bond in complexes 4 or 5, respectively. This, however, supports a butterfly geometry, which is isostructural to the starting carbonyl complex Ni2Cp2(mu-CO)2.     

Multiple Reaction Pathways Operating in the Mechanism of Vinylogous Mannich‐Type Reaction Activated by a Water Molecule

A systematic search for reaction pathways for the vinylogous Mannich‐type reaction was performed by the artificial force induced reaction method. This reaction affords δ‐amino‐γ‐butenolide in one pot by mixing 2‐trimethylsiloxyfuran, imine, and water under solvent‐free conditions. Surprisingly, the search identified as many as five working pathways. Among them, two concertedly produce anti and syn isomers of the product. Another two give an intermediate, which is a regioisomer of the main product. This intermediate can undergo a retro‐Mannich reaction to give a pair of intermediates: an imine and 2‐furanol. The remaining pathway directly generates this intermediate pair. The imine and 2‐furanol easily react with each other to afford the product. Thus, all of these stepwise pathways finally converge to give the main product. The rate‐determining step of all five (two concerted and three stepwise) pathways have a common mechanism: concerted Si? O bond formation through the nucleophilic attack of a water molecule on the silicon atom followed by proton transfer from the water molecule to the imine. Therefore, these five pathways have comparable barriers and compete with each other.     

Stereoselective [2,3]-sigmatropic rearrangements of unstabilized nitrogen ylides

The steric course of the [2,3]-rearrangement of several unstabilized nitrogen ylides has been investigated. The reactions proceed cleanly through an anti transition state, affording modest to good yields of a single diastereomer of the product. In two examples containing an N-cinnamyl group, a competing [1,2]-rearrangement affords a minor product.     

One-dimensional mapping of gamma emitting radionuclides in support of forensic examination

The development of two generations of a one-dimensional gamma mapping system is described. These systems use high-Z shielding, linear stage, and a high-purity germanium detector. Application to items of forensic interest is described and results for such items are presented. The presented results show the fission product (¹³⁷Cs) and activation product (⁶⁰Co) distributions along one-dimension of an archival item.     

甲烷在Mo/HZSM-5催化剂上的无氧转化─在隔离活性位上的反应

报道了无氧条件下甲烷在Ｍｏ／ＨＺＳＭ－５催化剂上转化为高碳的碳氢化合物的新途径。主要产物苯是经由乙烯聚合而成。此反应可能在两个隔离活性位上进行。乙烯作为甲烷活化的初始产物主要在分子筛外表面Ｍｏ活性位上形成,芳烃在分子筛的孔道内Ｂ酸位上形成。因此,我们认为该过程是乙烯中间产物由外表面扩散到分子筛孔道内形成芳烃。     

Experimental and theoretical studies on the radical-cation-mediated imino-Diels-Alder reaction

The feasibility of an electron transfer imino-Diels-Alder reaction between N-benzylideneaniline and arylalkenes in the presence of a pyrylium salt as a photosensitizer has been demonstrated by a combination of product studies, laser flash photolysis (LFP), and DFT theoretical calculations. A stepwise mechanism involving two intermediates and two transition states is proposed.     

Further studies on the pinacol coupling reaction

The pinacol coupling of R(+)3-methylcyclohexanone gives a product distribution $\text{dependent on the mode of coupling}$. Similar changes in product composition are also seen in the coupling of 4-methylcyclohexanone and in the mixed coupling of 3-methylcyclohexanone with cyclohexanone. In $\text{all cases studied}$, the [Al-Hg] method results in products having an axial methyl group. An X-ray structure of a product containing two axial methyl groups is presented.     

On the Mechanism of the Asymmetric Aldol Addition of Chiral N-Amino Cyclic Carbamate Hydrazones: Evidence of Non-Curtin–Hammett Behavior

he mechanistic details of the aldol addition of N-amino cyclic carbamate (ACC) hydrazones is provided herein from both an experimental and computational perspective. When the transformation is carried out at room temperature the anti-aldol product is formed exclusively. Under these conditions the anti- and syn-aldolate intermediates are in equilibrium and the transformation is under thermodynamic control. The anti-aldolate that leads to the anti-aldol product was calculated to be 3.7 kcal mol⁻¹ lower in energy at room temperature than that leading to the syn-aldol product, which sufficiently accounts for the exclusive formation of the anti-aldol product. When the reaction is conducted at −78 °C it is under kinetic control and favors formation of the syn-aldol addition product. In this case, it was found that a solvent separated aza-enolate anion and aldehyde form a σ-intermediate in which the lithium cation is coordinated to the aldehyde. The σ-intermediate collapses with a very small activation barrier to form the β-alkoxy hydrazone intermediate. The chiral nonracemic lithium aza-enolate discriminates between the two diastereotopic faces of the pro-chiral aldehyde, and there is no rapid direct pathway that interconverts the two diastereomeric intermediates. Consequently, the reaction does not follow the Curtin–Hammett principle and the stereochemical outcome at low temperature instead depends on the relative energies of the two σ-intermediates.     

Decomposition of excited electronic state s-tetrazine and its energetic derivatives

Decomposition of excited electronic state s-tetrazine and its energetic derivatives, such as 3-amino-6-chloro-1,2,4,5-tetrazine-2,4-dioxide (ACTO), and 3,3(')-azobis (6-amino-1,2,4,5-tetrazine)-mixed N-oxides (DAATO(3.5)), is investigated through laser excitation and resonance enhanced multi photon ionization techniques. The N(2) molecule is detected as an initial product of the s-tetrazine decomposition reaction, through its two photon, resonance absorption transitions [a(") (1)Σ(g)(+) (v(') = 0) ← X (1)Σ(g)(+) (v(") = 0)]. The suggested mechanism for this reaction is a concerted triple dissociation yielding rotationally cold (～20 K) ground electronic state N(2) and 2 HCN molecules. The comparable decomposition of excited electronic state ACTO and DAATO(3.5) yields an NO product with a cold rotational (～20 K) but a hot vibrational (～1200 K) distribution. Thus, tetrazine and its substituted energetic materials ACTO and DAATO(3.5) evidence different decomposition mechanisms upon electronic excitation. N(2)O is excluded as a potential intermediate precursor of the NO product observed from these two s-tetrazine derivatives through direct determination of its decomposition behavior. Calculations at the CASMP2∕CASSCF level of theory predict a concerted triple dissociation mechanism for generation of the N(2) product from s-tetrazine, and a ring contraction mechanism for the generation of the NO product from the energetic s-tetrazine derivatives. Relaxation from S(n) evolves through a series of conical intersections to S(0), upon which surface the dissociation occurs in both mechanisms. This work demonstrates that the substituents on the tetrazine ring change the characteristics of the potential energy surfaces of the derivatives, and lead to a completely different decomposition pathway from s-tetrazine itself. Moreover, the N(2) molecule can be excluded as an initial product from decomposition of these excited electronic state energetic materials.