''''98诺贝尔化学奖简介

1998年10月13日,瑞典皇家科学院宣布:将1998年度诺贝尔化学奖授予两位成就卓著的量子化学家--美国加利福尼亚大学的沃尔特·库恩 (Walter Kohn, 1923年出生) 和美国西北大学的约翰·波普尔 (John A. Pople, 1925年出生),以奖励沃尔特·库恩的密度泛函理论和约翰*波普尔的量子化学计算方法对化学的巨大贡献.在瑞典皇家科学院发布的公告中,量子化学被提到前所未有的重要地位--量子化学理论和计算的丰硕成果被认为正在引起整个化学的革命.量子化学家几十年的辛勤耕耘得到了充分的肯定.这标志着古老的化学已发展成为理论和实验紧密结合的科学.     

′98诺贝尔化学奖简介

１９９８年１０月１３日，瑞典皇家科学院宣布：将１９９８年度诺贝尔化学奖授予两位成就卓著的量子化学家——美国加利福尼亚大学的沃尔特·库恩（ＷａｌｔｅｒＫｏｈｎ，１９２３年出生）和美国西北大学的约翰·波普尔（ＪｏｈｎＡ．Ｐｏｐｌｅ，１９２５年出生），以奖...     

注重能力培养 拓宽学生思路──’98全国高中学生化学竞赛实验部分情况总结

受中国化学会委托,河南省化学会和郑州大学共同承办了1998年度全国高中学生化学竞赛盛冬令营活动,并取得了圆满的成功。现将竞赛中的实验部分情况作一说明。     

Gaussian 98在有机化学教学中的应用

Gaussian 98软件可以展示反应的途径及反应机理,能够计算反应的相关数据,尤其是该软件在有机化学教学中的应用,更能显示出在教学中的应用优势.     

Synthesis of a secretoglobin 3A2 type C (98–139) fragment by Dawson’s native chemical ligation

A secretoglobin 3A2 type C (98–139) peptide was synthesized by native chemical ligation between ¹¹⁵Ile and ¹¹⁶Cys residues using Dawson’s linker. The peptide-N-acyl-benzimidazolinone-glycine amide, a C-terminal thioesters precursor, was provided from 3-amino-4-(methylamino)benzoic acid. In addition, an N-terminal cysteine fragment, the (116–139) peptide, was prepared by ordinary Fmoc-solid phase peptide synthesis. Native chemical ligation of the (98–115) fragment with the Dawson’s linker and the (116–139) peptide smoothly proceeded to give SCGB3A2 type C (98–139) peptide.     

Synthesis of Some Novel Phenyl Substituted Oxothiazolidin- 1’’,3’’,4’’-thiadiazolo-[3’,4’-b]thiazoline of 3β-Substituted Cholestane

Three title compounds 4a—4c have been synthesized by the cyclodehydration of 1’-benzylidine-4’-(3β-substituted-5α-cholestane-6-yl)thiosemicarbazones 2a—2c with thioglycolic acid followed by the treatment with cold conc. H2SO4 in dioxane. The compounds 2a—2c were prepared by condensation of 3β-substituted-5α-cholestan- 6-one-thiosemicarbazones 1a—1c with benzaldehyde. These thiosemicarbazones 1a—1c were obtained by the reaction of corresponding 3β-substituted-5α-cholestan-6-ones with thiosemicarbazide in the presence of few drops of conc. HCl in methanol. The structures of the products have been established on the basis of their elemental, analytical and spectral data.     

初中化学实验教学培养学生素质的几个问题与对策──’98年中考实验操作考试给我们的启示

我们知道,化学实验教学对培养学生素质有着其他教学方法和手段不可替代的重要作用,它是实施素质教育的有效途径.为加强实验教学,我省从1995年开始,逐步实行了"中考加试物理、化学实验操作,成绩计入录取总分"的制度.     

MC98-A型多功能极谱仪研制

以８０９８单片机作智能部件的小型多功能极谱仪，采用ＳＴＤ标准总线结构，汉字菜单式提示，人－机对话方式操作。以阳极溶出和电位溶出分析为主，用三种定量分析方法直接显示，打印出测试曲线和分析结果。     

OH(3) (-) and O(2)H(5) (-) double Rydberg anions: predictions and comparisons with NH(4) (-) and N(2)H(7) (-)

A low barrier in the reaction pathway between the double Rydberg isomer of OH(3) (-) and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH(4) (-). Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state's electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH(3) (-) DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O(2)H(5) (-) species. Three O(2)H(5) (-) minima with H(-)(H(2)O)(2), hydrogen-bridged, and DRA-molecule structures resemble previously discovered N(2)H(7) (-) species and have well separated VEDEs that may be observable in anion photoelectron spectra.     

An Efficient Synthesis of Optically Pure (R)- and (S)-2-(aminomethyl)alanine ((R)- and (S)-ama) and (R)- and (S)-2-(aminomethyl)leucine ((R)- and (S)-aml)

An efficient synthesis of enantiomerically pure (R)- and (S)-2-(aminomethyl)alanine ((R)- and (S)-Ama) 1a and (R)- and (S)-2-(aminomethyl)leucine ((R)- and (S)-Aml) 1b is described (Schemes 1 and 2). Resolution of the racemic amino acids was achieved using L -phenylalanine cyclohexylamide ( 2 ) as chiral auxiliary. The free amino acids 1a, b were converted to the N^α-Boc,N^γ-Z-protected derivatives 11a, b (Scheme 3) ready for incorporation into peptides. Based on the three crystal structures of the diastereoisomeric peptides 8a, 8b , and 9b , the absolute configurations in both series were determined. β-Turn type-I geometries were observed for structures 8b and 9b , whereas 8a crystallized in an extended backbone conformation.     

Mixed ligand titanium(IV) complexes. Chlorobis(dithiocarbamato)bis(methylsalicylato)titanium(IV) andbis(dithiocarbamato)bis(methylsalicylato)titanium(IV)

Summary Dichlorobis(methylsalicylato)titanium(IV) reacts with potassium or amine salts of dialkyl or diaryl dithiocarbamates in 11 and 12 molar ratios in anhydrous benzene (room temperature) or in boiling CH₂Cl₂ to yield mixed ligand complexes: (AcOC₆H₄O)₂ Ti(S₂CNR₂)Cl (1) and (AcOC₆H₄O)₂ Ti(S₂CNR₂)₂ (2), R=Et, n-Pr, n-Bu, cyclo-C₄H₈ and cyclo-C₅H₁₀. These compounds are moisture sensitive and highly soluble in polar solvents. Molecular weight measurement in conjunction with i.r.,¹H and¹³C n.m.r. spectral studies suggest coordination number 7 and 8 around titanium(IV) in (1) and (2) respectively.     

Bis(trifluoroacetyl) peroxide, CF(3)C(O)OOC(O)CF(3)

Pure, highly explosive CF(3)C(O)OOC(O)CF(3) is prepared for the first time by low-temperature reaction between CF(3)C(O)Cl and Na(2)O(2). At room temperature CF(3)C(O)OOC(O)CF(3) is stable for days in the liquid or gaseous state. The melting point is -37.5 degrees C, and the boiling point is extrapolated to 44 degrees C from the vapor pressure curve log p = -1875/T + 8.92 (p/mbar, T/K). Above room temperature the first-order unimolecular decay into C(2)F(6) + CO(2) occurs with an activation energy of 129 kJ mol(-1). CF(3)C(O)OOC(O)CF(3) is a clean source for CF(3) radicals as demonstrated by matrix-isolation experiments. The pure compound is characterized by NMR, vibrational, and UV spectroscopy. The geometric structure is determined by gas electron diffraction and quantum chemical calculations (HF, B3PW91, B3LYP, and MP2 with 6-31G basis sets). The molecule possesses syn-syn conformation (both C=O bonds synperiplanar to the O-O bond) with O-O = 1.426(10) A and dihedral angle phi(C-O-O-C) = 86.5(32) degrees. The density functional calculations reproduce the experimental structure very well.