Electron attachment to MoF6, ReF6, and WF6; reaction of MoF6(-) with ReF6 and reaction of Ar+ with MoF6

Rate constants were measured for electron attachment to MoF(6), ReF(6), and WF(6) in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF(6) on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF(6) is (2.3+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only MoF(6) (-) is formed in the temperature range of 297-385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF(6) occurs with a rate constant of (2.4+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only ReF(6) (-) is produced. MoF(6) (-) reacts with ReF(6) to form ReF(6) (-) on essentially every collision, showing definitively that the electron affinity of ReF(6) is greater than that of MoF(6). A rate constant of (5.0+/-1.3)x10(-10) cm(3) s(-1) was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar(+) with MoF(6) was found to produce MoF(5) (+)+F, with a rate constant of (1.8+/-0.5)x10(-9) cm(3) s(-1). WF(6) attaches electrons so slowly at room temperature that the attachment rate was below detection level (< or =10(-12) cm(3) s(-1)). By 552 K, the attachment rate constant reaches a value of (2+/-1)x10(-10) cm(3) s(-1).     

C60NH5/6, 6/6异构体的理论研究

用半经验的AM1, PM3及ab initio方法对C60NH两种异构体的结构及光谱进行了理论计算。结果表明, 具有开环结构的C60NH的5/6异构体稳定性要高于具有闭环结构的6/6异构体。计算了两种异构体开环与闭环过程的反应坐标, 发现6/6开环异构体是势能面上的一局部最小点, 而5/6闭环异构体不存在6/6异构体的H可以在两种镜面异构体之间快速翻转, 使其核磁共振谱呈现C2v对称性。通过振动分析确认了所优化的构型确实为势能面的能量最低点, 并得到了C60NH各异构体的红外光谱。     

Facile Syntheses of (6S)-6-Fluoroshikimic Acid and (6R)-6-Hydroxyshikimic Acid

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｓｈｉｋｉｍａｔｅｐａｔｈｗａｙｉｓａｎｉｍｐｏｒｔａｎｔｂｉｏｓｙｎ ｔｈｅｔｉｃｓｅｑｕｅｎｃｅｉｎ ｐｌａｎｔｓ ,ｆｕｎｇｉａｎｄｍｉｃｒｏｏｒｇａｎｉｓｍｓｆｏｒｔｈｅｃｏｎｖｅｒｓｉｏｎｏｆｃａｒｂｏｈｙｄｒａｔｅｓｔｏｔｈｅａｒｏｍａｔｉｃａｍｉｎｏａｃｉｄｓ (Ｌ ｐｈｅｎｙｌａｌａｎｉｎｅ ,Ｌ ｔｙｒｏｓｉｎｅａｎｄＬ ｔｒｙｐｔｏｐｈａｎ)ａｎｄｐｒｅｃｕｒｓｏｒｓｔｏｔｈｅｆｏｌａｔｅｃｏｅｎｚｙｍｅｓ ,ａｌｋａｌｏｉｄｓａｎｄｖｉｔａｍｉｎｓ[1] .Ａｓ…     

Arachno, nido, and closo aromatic isomers of the Li6B6H6 molecule

We analyzed chemical bonding in low-lying isomers of the recently computationally predicted B(6)H(6)Li(6) molecule. According to our calculations the benzene-like B(6)H(6)Li(6) (D(2h), (1)A(1g)) arachno structure with the planar aromatic B(6)H(6)(6-) anion is the most stable one. A nido isomer with two aromatic B(6)H(6)(4-) (pentagonal pyramid) and Li(3)(+) (triangular) moieties, which can be considered as derived from the global minimum structure through a two-electron intramolecular transfer from B(6)H(6)(6-) to three Li(+) cations, was found to be 10.7 kcal/mol higher in energy. A closo isomer with three aromatic moieties (octahedral B(6)H(6)(2-) and two Li(3)(+)) was found to be 31.3 kcal/mol higher in energy than the global minimum. Another isomer with three aromatic moieties (two B(3)H(3)(2-) and Li(3)(+)) was found to be substantially higher in energy (74.4 kcal/mol). Thus, the intramolecular electron transfers from the highly charged B(6)H(6)(6-) anion to cations are not favorable for the B(6)H(6)Li(6) molecule, even when a formation of three-dimensional aromatic B(6)H(6)(2-) anion and two sigma-aromatic Li(3)(+) cations occurs in the closo isomer.     

Reaction of 6-quinoline aldehyde with rhodanines and 2, 6-dimethylquinoline

The crotonaldehyde type of condensation of 6-quinolylaldehyde and its methiodide with 3-methyl-3-ethyl-, and 3-allylrhodanines is investigated. 5-(Quinolidene-6-)-3-alkylrhodanines and their monomethiodides are synthesized. 2-[2-(Quinolyl-6) ethenyl]-6-methylquinoline is prepared by condensing 6-quinolylaldehyde with 2,6-dimethylquinoline.     

In search of benzene-like Sn6(6-): synthesis of Na4CaSn6 with interconnected cyclohexane-like Sn6(6-)

The title compound was synthesized in an attempt to produce stacked benzene-like Sn6(6-) rings separated by alkaline-earth cations in analogy with the recently reported stacks of aromatic cyclopentadienyl-like Sn5(6-) in Na8BaSn6 (in addition to isolated Sn4- anions). The resulting compound, synthesized from a stoichiometric mixture of the elements at high temperature, has the "correct" stoichiometry with six tin atoms and six positive charges. However, the rings of Sn6(6-) are puckered into chair-type cyclohexanes that are interconnected into isolated cylindrical tubes stuffed with Ca2+ between the rings. Such tubes, if fused to each other, form the hexagonal diamond structure. The new compound is electronically balanced according to magnetic and four-probe resistivity measurements. Reported are also the synthesis and properties of Na10EuSn12 and Na10YbSn12 which are isostructural with the known Na10CaSn12.     

Synthesis of optically active 3-alkoxy-6-hydroxymethyl-6-methyl-2-cyclohexenone

Optically active 3-alkoxy-6-hydroxymethyl-6-methyl-2-cyclohexenone and 6-acetoxymethyl-3-alkoxy-6-methyl-2-cyclohexenone were efficiently obtained by lipase-catalyzed kinetic resolution. (R)-6-Acetoxymethyl-3-(methoxymethoxy)-6-methyl-2-cyclohexenone was converted to the synthetic intermediate of cassiol.     

Isomerization of B_6,B_6~- and B_6~+ clusters

The interconversions between isomers with the same spin multiplicity of neutral B6 and charged B6-and B6+ clusters have been investigated at the B3LYP/6-311+G level of theory,including determination of the minimum energy pathways with transition states connecting the corresponding reactants and products.In dynamic calculations,26 isomers were optimized,including 11 novel isomers.In order to further refine the energies,single-point B3LYP/6-311+G(3df) calculations were carried out on the corresponding B3LYP/6...     

新法合成6-烷氧基和6-氨基鸟嘌呤核苷衍生物

以鸟嘌呤为核苷为原料,经酯化、再在缩合剂4-氯苯磷酰二氯和1,2,4-三氮唑存在下与吡啶反应,得鸟嘌呤核苷N-6吡啶盐中间体(2),该中间体2分别与NH~3/CH~3OH、Et~3N/CH~3OH、Et~EN/CH~3CH~2OH在室温反应,可方便的合成6-NH~2、6-OCH~3和6-OCH~2CH~3-9-(β-D-呋喃核糖)鸟嘌呤衍生物。     

Reactions of 6-hydrazino-, 6-hydroxylaminopurines and related derivatives

7H-Tetrazolo[5,1-i]purine was prepared by nitrosation of 6-hydrazinopurine and by reaction of 6-chloropurine with sodium azide; it was converted to adenine upon catalytic hydrogenation. 6-Hydroxylaminopurine was oxidized to 6-nitrosopurine with manganese dioxide, while alkaline treatment of the former gave 6,6′-azoxypurine. Nitrosation of 6-hydroxylaminopurine afforded 6-(N-nitroso)hydroxylaminopurine. Reaction of 6-chloropurine with 6-hydrazinopurine led to 6,6′-bisadenine; the corresponding ribosyl derivatives gave 6,6′-bisadenosine. Upon air oxidation, 6,6′-bisadenine was converted into 6,6′-azopurine. The related 6-thiosemicarbazino- and 6-(N-methyl)ureidopurine derivatives are also described. 6-N-(Nitroso)hydroxylaminopurine showed an inhibitory activity against several mouse tumors and leukemias.     

Synthesis of the 6-6-6 tricyclic skeleton of the anti-influenza A diterpene wickerol A

A five-step synthesis of the 6-6-6 tricyclic skeleton of the diterpene wickerol A is described. The synthesis features a diastereoselective d-proline-mediated Robinson annulation and N-heterocyclic carbene-catalyzed Stetter reaction as key transformations to give the tricyclic carbon skeleton of this promising anti-influenza A natural product.     

Synthese und Eigenschaften von 6-Desoxy-6-halogen-Derivaten der L-Ascorbinsäure

Synthesis and Properties of 6-Deoxy-6-halogeno-Derivatives of L -Ascorbic Acid 6-Deoxy-6-chloro-, -6-bromo-, -6-iodo- and -6-fluoro derivatives of L -ascorbic acid have been synthesized and characterized. The physiological properties of the chloro derivative have been investigated. It shows a high antiscurvy activity. The chloro- and bromo-derivatives have been reduced to the corresponding deoxy compound, which is an interesting chiral intermediate for the preparation of rare ω-deoxy sugars.     

二氢卟吩e~6-6-酰胺衍生物的合成

首次报道了以蚕沙叶绿素初提物为基础原料,经酸降解得到含焦脱镁叶绿酸a和脱镁叶绿酸a的混合物,不经分离直接与胺类反应使脱镁叶绿酸a的戊酮环(V)裂开,合成得11种二氢卟吩e~6-6-酰胺衍生物。提供了一种合成二氢卟吩酰胺的新方法。     

Ordnungszustände im system polyamid-6 und polyamid-6, 6

Blends of PA-6 and PA-6,6 were studied by DSC for different conditions of crystallization. All samples were characterized by x-ray diffraction. From dilute solution the components crystallize in separate modifications. In the melt both components are compatible. PA-6- and PA-6,6-segments are linked together. During rapid quenching of the melt in the samples of about equal composition of PA-6 and PA-6,6 a modification is formed possibly built by a three-dimensional network of hydrogen bonds between PA-6- and PA-6,6-segments. If the samples of the same composition are annealed at 25 K below the melting temperatures of PA-6 and PA-6,6 for 3 hours in each case a modification appears as in quenched samples in addition to only partially ordered crystallites of PA-6 and PA-6,6. Despite optimal annealing there is no complete separation of the components.     

On the structure and chemical bonding of Si6(2-) and Si6(2-) in NaSi6(-) upon Na+ coordination

Photoelectron spectroscopy was combined with ab initio calculations to elucidate the structure and bonding in Si6 2- and NaSi6 -. Well-resolved electronic transitions were observed in the photoelectron spectra of Si6 - and NaSi6 - at three photon energies (355, 266, and 193 nm). The spectra of NaSi6 - were observed to be similar to those of Si6 - except that the electron binding energies of the former are lower, suggesting that the Si6 motif in NaSi6 - is structurally and electronically similar to that in Si6 -. The electron affinities of Si6 and NaSi6 were measured fairly accurately to be 2.23+/-0.03 eV and 1.80+/-0.05 eV, respectively. Global minimum structure searches for Si6 2- and NaSi6 - were performed using gradient embedded genetic algorithm followed by B3LYP, MP2, and CCSDT calculations. Vertical electron detachment energies were calculated for the lowest Si6 - and NaSi6 - structures at the CCSD(T)/6-311+G(2df), ROVGF/6-311+G(2df), UOVGF/6-311+G(2d), and time-dependent B3LYP/6-311+G(2df) levels of theory. Experimental vertical detachment energies were used to verify the global minimum structure for NaSi6 -. Though the octahedral Si6 2-, analogous to the closo form of borane B6H6 2-, is the most stable form for the bare hexasilicon dianion, it is not the kernel for the NaSi6 - global minimum. The most stable isomer of NaSi6 - is based on a Si6 2- motif, which is distorted into C2v symmetry similar to the ground state structure of Si6 -. The octahedral Si6 2- coordinated by a Na+ is a low-lying isomer and was also observed experimentally. The chemical bonding in Si6 2- and NaSi6 - was understood using natural bond orbital, molecular orbital, and electron localization function analyses.     

Ultraviolet and infrared photodissociation of Si(+)(C6H6)n and Si(+)(C6H6)(n)Ar clusters

Ion-molecule complexes of the form Si(+)(C6H6)n and Si(+)(C6H6)(n)Ar are produced by laser vaporization in a pulsed nozzle cluster source. These clusters are mass-selected and studied with ultraviolet (355 nm) photodissociation and resonance-enhanced infrared photodissociation spectroscopy in the C-H stretch region of benzene. In the UV, Si(+)(C6H6)n clusters (n = 1-5) fragment to produce the Si(+)(C6H6)n mono-ligand species, suggesting that this ion has enhanced relative stability. IR photodissociation of Si(+)(C6H6)n complexes occurs by the elimination of benzene, while Si(+)(C6H6)(n)Ar complexes lose Ar. Resonances reveal C-H vibrational bands in the 2900-3300 cm(-1) region characteristic of the benzene ligand with shifts caused by the silicon cation bonding. The IR spectra confirm that the major component of the Si(+)(C6H6)n ions studied have the pi-complex structure rather than the isomeric insertion products suggested previously.     

Synthesis of [6-6-6] ABE tricyclic ring analogues of methyllycaconitine

A new synthesis of the bridged [6-6-6] ABE tricyclic ring analogues of methyllycaconitine with the C-1 oxygenated substituents has been developed using an efficient aza-annulation of β-enamino ketone followed by a facile decarboxylation to form BE rings. Subsequent elaboration to form the A ring was achieved by a transannular acyl radical cyclization with concomitant equipment of the key C-1 oxygen functionality.     

Zur Kenntnis von NiPtF6 und CdPtF6

Anotation to Compounds MPtF₆ (M = Ni, Cd) Yellow single crystals of M¹¹PtF₆ (M¹¹ = Ni, Cd) have been obtained for the first time and investigated by X-ray methods. The powder data of the compounds are confirmed. Both samples are isostructural to LiSbF₆, space group R3 -C (Nr. 148) with a = 500.5(3) pm, c = 1375.6(7) pm for NiPtF₆ and a = 511.56(9) pm, c = 1460.3(4) pm for CdPtF₆, Z = 3.     

Studies of the kinetics and thermochemistry of the forward and reverse reaction Cl + C6H6 = HCl + C6H5

The laser flash photolysis resonance fluorescence technique was used to monitor atomic Cl kinetics. Loss of Cl following photolysis of CCl4 and NaCl was used to determine k(Cl + C6H6) = 6.4 x 10(-12) exp(-18.1 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 578-922 K and k(Cl + C6D6) = 6.2 x 10(-12) exp(-22.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 635-922 K. Inclusion of literature data at room temperature leads to a recommendation of k(Cl + C6H6) = 6.1 x 10(-11) exp(-31.6 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) for 296-922 K. Monitoring growth of Cl during the reaction of phenyl with HCl led to k(C6H5 + HCl) = 1.14 x 10(-12) exp(+5.2 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 294-748 K, k(C6H5 + DCl) = 7.7 x 10(-13) exp(+4.9 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 292-546 K, an approximate k(C6H5 + C6H5I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) over 300-750 K, and an upper limit k(Cl + C6H5I) < or = 5.3 x 10(-12) exp(+2.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 300-750 K. Confidence limits are discussed in the text. Third-law analysis of the equilibrium constant yields the bond dissociation enthalpy D(298)(C6H5-H) = 472.1 +/- 2.5 kJ mol(-1) and thus the enthalpy of formation Delta(f)H(298)(C6H5) = 337.0 +/- 2.5 kJ mol(-1).