CAST/CNMR: highly accurate C NMR chemical shift prediction system considering stereochemistry

Accurate, practical prediction of ¹³C NMR chemical shifts has been achieved with a new system, CAST/CNMR, taking account of stereochemistry. The CAST/CNMR system has solved the critical problem of the accurate distinction of differences and similarities in stereochemical structures around a specific carbon, which has not yet been achieved by any other database-oriented system for prediction of ¹³C NMR chemical shifts. CAST/CNMR uses a three-dimensional structural database together with a ¹³C NMR spectral database. Absolute/relative configurational and conformational structural information are described by the CAST (CAnonical-representation of STereochemistry) coding method. This paper provides an overview of the CAST/CNMR system, and describes its application to two natural products as examples.     

CH_3自由基和O（~3P）反应机理的量子化学研究

用分子轨道从头计算MP2（full）方法和密度泛函理论（DFT）中的B3LYP方法 研究了CH_3自由基和三线态O原子反应的微观机理，优化得到了反应途径上的反应 物、过渡态、中间体和产物的几何构型，通过振动分析对过渡态和中间体构型进行 了确认，在G3不平上计算了能量，同时用经典过渡态理论对该反应的绝对速率常数 进行了理论计算。研究结果表明：CH_3自由基与O（~3P）反应有四条不同的放热反 应通道，主反应通道为IM1→TS1→CH_2O + H，同时反应可彻底裂解生成CO, H_2 及H。     

On an alternative functional equation related to the Cauchy equation

We consider the following problem: Let (G, +) be an abelian group,B a complex Banach space,a, bB,b0,M a positive integer; find all functionsf:G B such that for every (x, y) G ×G the Cauchy differencef(x+y)–f(x)–f(y) belongs to the set {a, a+b, a+2b, ...,a+Mb}. We prove that all solutions of the above problem can be obtained by means of the injective homomorphisms fromG/H intoR/Z, whereH is a suitable proper subgroup ofG.     

Miniaturization of a thalliumiodide photodissociation laser

We report on the operation of a thallium photodissociation laser with an active medium in the form of a thin layer on a quartz wall. Laser emission has been obtained with layer thicknesses below 100 m. This gas laser seems to be feasible with an active volume as small as 10^–1 to 10^–2 mm³.     

Simultaneous determination of C1−C8 n-alkyl acetates and corresponding mono-, di- and trichloroacetates on glass capillary columns with programmed temperature rise

Summary Gas chromatography of mixtures of aliphaticn-alkyl acetates (CH₃–COOR), chloroacetates (CHCl₂–COOR), dichloroacetates (CHCl₂–COOR) and trichloroacetates (CCl₃–COOR), where the alcohol chain length (R) varied between 1 and 8, has been studied on SE-30, Carbowax 20M and OV-351 glass capillary columns with programmed temperatures from 50°C at 2, 4, 6, 8 and 10°C/min. Compounds in the homologous series are eluted in the direct order from methyl ton-octyl acetate. The isomeric chloro esters are eluted on SE-30 according to their boiling points in the order: mono-, di- and trichloro isomer, whereas on polar columns di- and trichloro esters are eluted in the reverse order. The complete separation of all 32 individual components from the mixture could not be reached by any single column, the best separation occurred on SE-30. The mixture can, however, be separated by using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the retention order discussed.     

Photochemistry of β, γ-unsaturated ketones-V: The direct irradiation of some γ-phenyl β, γ-enones

The photochemistry of some members of the two series of γ-phenyl substituted acyclic β, γ-unsaturated ketones 1 and 2 upon direct irradiation with γ 310nm has been investigated, viz 1c–1h and 2b+2c.The alkyl substituted (E)-5-phenyl-4-penten-2-ones 1c–1h yield the corresponding 1,3-acyl shift products and (Z)-isomers, and 1g and 1h in addition two decarbonylated products. 2b only yields the (Z)-isomer and some benzaldehyde, but 2c yields the 1,3-acyl shift product, the ODPM product, three hydrocarbons formed by disproportionation of the allyl radical, and some benzaldehyde. The β-phenyl β, γ-UK 3a proved to be photostable. The 1,3-acyl shift products of 1c–1h result mainly from the singlet excited state in a cage radical process. The exclusive formation of the (E)-configuration of the 1,3-acyl shift product is explained in terms of conformational preference of the intermediate allyl radical. It is proposed that the formation of the (Z)-isomer proceeds from ¹T(π -π^*) which is populated according to

. Evidence is presented which supports the proposed mechanism.The β,γ-UK 2b containing a benzoyl moiety leads to a higher degree of (E)-(Z) isomerization than the corresponding 1d which has an acetyl moiety.The triplet energies of (E)- and (Z)-1h are 56 and ca 70 kcal/mol respectively.     

273.15 K下Li2B4O7-LiCl-H2O体系热力学性质的等压研究及离子作用模型

用等压法研究了273.15 K下Li₂B₄O₇-LiCl-H₂O体系不同质量摩尔浓度分数的等压平衡浓度和水活度; 计算了LiCl和Li₂B₄O₇混合盐溶液的渗透系数等热力学性质. 用273.15 K下的实验数据对Pitzer离子相互作用模型进行了参数化研究, 拟合求取了273.15 K下Pitzer离子相互作用参数, 用获得的参数计算了LiCl和Li₂B₄O₇在Li₂B₄O₇-LiCl-H₂O体系中的活度系数. 273.15 K下由相应的Pitzer模型计算的渗透系数值与实验结果一致. 这对完善含锂、硼盐湖卤水体系的热力学模型具有重要意义.     

Phosphan-, Phosphit- und Phosphido-Komplexe des Vanadiums(V)

Phosphane, Phosphite, Phosphido, Complexes of Vanadium(V) Complex formation of tert-butylimidovanadium(V)trichloride ( 1 ) with phosphanes und phosphites has been studied. Syntheses of phosphidovanadium(V) compounds ^tC₄H₉N?VCp(NH^tC₄H₉)[P(SiMe₃)₂] and ^tC₄H₉N?VCp(NⁱProp₂)(PR₂) (R?SiMe₃, Ph) are described starting from the corresponding chlorovanadium(V) complexes. The reaction of 1 with silver hexafluorophosphate yields a bis(fluoro)phosphidovanadium(IV complex [(μ-PF₂)₂V₂Cl₂)(N^tC₄H₉)₂]; as primary intermediate product of the unknown redox reaction a cationic vanadium(V) complex [^tC₄H₉N?VCl₂ · PPh₃]⁺PF₆^? has been isolated. 1 reacts with an excess of diisopropylamine forming ^tC₄H₉N?V(NⁱProp₂)Cl₂ ( 16 ); in addition the following diisopropylamido-tert-butylimidovanadium(V) compounds ^tC₄H₉N?VCp(NⁱProp₂)Cl ( 3 ) and ^tC₄H₉N?V(NⁱProp₂)X₂ (X?CH₂CMe₃, O^tC₄H₉, CH₃COO) has been prepared. All compounds obtained are characterized by ¹H, ⁵¹V, ³¹P NMR spectroscopy. The X-ray diffraction analysis of 16 and 3 indicate a planar coordination sphere of the amido nitrogen atom.     

Stereoselective reduction of arteannuin B and its chemical transformations

Absolute stereochemistry of dihydroarteannuin B 5 obtained by the reduction of arteannuin B 3 with Ni₂B, NaBH₄ or CdCl₂-Mg-MeOH-H₂O has been established by 2D NMR and single crystal X-ray diffraction studies. Some experiments aimed at the synthesis of dihydrodeoxyarteannuin B [C-4, 5 double bond isomer of 11] are also discussed.     

Two New Diterpenoids from Callicarpa pedunculata

Two new diterpenoids, pedunculatic acid A (= (4R,5α,7α)‐7‐ethoxy‐9β,13β‐dioxyabiet‐8(14)‐en‐18‐oic acid; 1 ) and pedunculatic acid B (= (4S,5α,12β)‐8β,14β‐epoxy‐12‐hydroxy‐11‐oxototaran‐19‐oic acid; 2 ), together with three known sesquiterpenoids, were isolated from the Chinese medicinal herb Callicarpa pedunculata R. Brown . Their structures were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR, and by high‐resolution mass spectrometry.