Ethenedithione (S=C=C=S): Does It Obey Hund's Rule?

Significantly higher in energy (24 kJ mol⁻¹) than the triplet ground state (³Σ_g⁻) is the ¹Δ_g state of ethenedithione (S=C=C=S), in agreement with Hund's rule. This result was obtained from high-level ab initio calculations. Thus, ethenedithione cannot, as had been proposed, be considered as the first example for the violation of Hund's rule in an equilibrium structure.     

Facile Synthesis of (S,S)‐1,2‐Diacylamides and (S,S)‐1,2‐Diamines with C 2‐Symmetry

A series of chiral vicinal tertiary diacylamides with C ₂‐symmetry was synthesized from (S)‐α‐phenylethylamine, different aromatic aldehydes, and oxalyl chloride. The diacylamides obtained were then reduced to afford chiral vicinal diamines with C ₂‐symmetry. We propose that the diacylamides existed in four stable conformational isomers in solution because of the dihedral angle between acylamide bonds.     

C(3P)与H2S反应的反应机理

1994年,苏梅克9号彗星撞击木星引起了木星大气成分的变化,研究发现撞击后木星大气中含有大量的含硫含碳的小分子和小自由基.因缺乏与这些物质相关的中间体的实验数据,研究它们的来源的工作难以进行.1998年,李远哲等[1]用交叉分子束实验研究了基态碳原子Ｃ(3Ｐ)与Ｈ2Ｓ的反应,得到主要产物ＨＣＳ.他们对反应所经历的中间体作了推测,并用从头计算方法计算了反应物、中间体和产物的能量,但对反应所经历的(反应物与中间体、中间体与中间体、中间体与产物之间的)过渡态没有进行探讨.众所周知,过渡态位垒的高低对是否能实现设定的反应是至关重要的…     

C(3P)与H2S反应的反应机理

The mechanisms of the C(3P)+H 2S→HCS+H and C(3P)+H 2S → HSC+H reactions have been studied at the UMP2/6-31G(d,p),UMP2/6-311G(d,p),and G2 levels, and six transition states and three intermediates have been located along the reaction paths. The predicted path for the C(3P)+H2S→HCS+H reaction is: C(3P)+H2S→IM1→TS1→IM2→TS4→HCS+H, in line with the reaction process suggested by Lee et al. [1] in which only the intermediates were given. Our energetic results indicate that the C(3P)+H2S→HCS+H reaction is more favorable than the C(3P)+H 2S→HSC+H reaction, in agreement with experiment.     

C(2×2)S/Fe(001)吸附体系的SCF-Xa-MS研究

采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。     

(S)-(-)-norlaudanosine和(S)-(-)-O,O-dimethylcoclaurine的合成

以高藜芦胺为起始原料,经N-磺酰化反应制得高藜芦磺酰胺(2);2分别与芳乙烯甲醚经对甲苯磺酸催化的Pictet-Spengler反应后用金属钠脱除Ts基团合成了(±)-norlaudanosine(5a)和(±)-O,O-dimethylcoclaurine(5b);使用半量拆分法,以N-乙酰-L-苯丙氨酸为拆分剂,制得(S)-(-)-5a和(S)-(-)-5b,其结构经1H NMR,13C NMR,IR,MS和HR-ESI-MS确证。     

CRYSTAL AND MOLECULAR STRUCTURE OF(μ-PhCH_2S)(μ-CH_3C(0)CH_2S)Fe_2(CO)_6

<正> The crystal and molecular structures of (μ-PhCH2S)(μ-CH3C(O)CH2S)-Fe2(CO)6 have been determined by X-ray diffraction technique. The complex has chemical formula of C16H12O7S2Fe2 and Mr=492.08. The crystals are tri-clinic, space group P1,with a=8.461(5), b=10.937(5), c=ll.419(4)A,α=81.61 (3), β=78.21(4),γ=71.04(4)°,V=974.5A3, Dc=1.68 gcm-3,μ(MoKα)=17.3cm-1, Z=2,F(000)=495.93. The final R was 0.038 for 2874 independent reflections.     

微生物酶催化制备人参皂苷20(S)-Rg2,20(S)-Rh1和20(S)-PPT

摘要 人参次级皂苷具有较强的抗癌、抗癌转移等药理活性,但由于在人参中含量少或不存在,因此以人参中含量较高的主要人参皂苷制备药效更高的人参次级皂苷不仅有必要,而且很有意义．本文以微生物Microbacterium esteraromaticum GS514的培养液中分离的粗酶为催化剂水解人参皂苷Re和Rg1,并通过1H NMR和13C NMR谱进行了水解产物的结构表征．实验结果表明,反应体系中无机盐NaCl的存在与否直接影响人参皂苷Re,Rg1与粗酶液的反应结果.人参皂苷与粗酶液直接反应,人参皂苷Re不发生反应,人参皂苷Rg1通过C6所连β-D-吡喃葡萄糖的选择性水解转化成人参皂苷F1.如果该反应是在无机盐NaCl存在下进行,人参皂苷Re通过对C20 所连β-D-吡喃葡萄糖的选择性水解定向转化为20(S)-人参皂苷Rg2;人参皂苷Rg1定向转化成20(S)-人参皂苷Rh1以及20(S)-原人参三醇（PPT）.这说明NaCl的加入激活了C20β-D-吡喃葡萄糖苷酶的活性,这对定向合成不同次级人参皂苷具有重要意义.     

C(2×2)S/Fe(001)吸附体系的SCF-X_α-MS研究

采用SCF-X_α-MS方法,对于C(2×2)S/Fe(001)吸附体系,选择Fe_5S和Fe_9S两种原子簇模型,研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明,S吸附于Fe(001)单晶表面具有较强的定域性质,S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化,其结果与X.S.Zhang等的ARPEFS的实验结果一致。     

~(13)C核磁共振(六)

分子式为C_6H_8O的哪一个化合物与图E-11符合? 取谱条件: 溶剂:CDCl_3(δ77.2三重峰) 浓度:50V/V％温度:28℃测定频率:22.63MHz 去偶:上——~1H偏共振去偶(500次) 下——~1H宽带去偶(100次) [解答]C_6H_8O含有三个双键当量。在~(13)C谱中找到一个羰基(δ198.65)以及一个C=C键(δ150.6及129.85)。还余下一个双键与三个次甲基(δ38.2,25.75及22.95)。总结起     

~(13)C核磁共振(五)

习题1 分子式为C_4H_(10)S的哪一个化合物符合图E-1的~(13)C谱?对此谱作出归属。取谱条件: 溶剂:CDCl_3(δ77.25处有三重峰,图中未画出) 浓度:50V/V％温度:28℃测定频率:22.63MHz 去偶:上——~1H偏共振去偶(200次) 下——~1H宽带去偶(100次)     

~(13)C核磁共振(七)

习题16 1,3,5-三硝基苯与丙酮在氢氧化钾的乙醇溶液存在下反应生成一种蓝紫色的Meisenheimer钾盐,见谱E-16。分析此谱并给出从谱所得最重要的论点以支持此盐的结构。取谱条件: 溶剂,(eD,),50(3,.7七重峰,Je-一20.5Hz) 浓度:饱和溶液温度:28℃测定频率:22.63 MHz 去偶.上.偶合谱(25000次),附有放大四倍的部分谱下:几H宽带去偶( 5000次)〔解答〕谱的归属     

~(13)C核磁共振(四)

9 ~(13)C自旋-晶格弛豫时间(T_1)的测量及应用 9.1 测定T_1的方法 9.1.1 倒向—恢复法此法是用(180°-τ-90°)_n脉冲系列作用于样品。磁化矢量M_0在180°脉冲作用下倒向(图20b),在自旋-晶格弛豫过程中,磁化矢量从-M_0经0到 M_0弛豫,在这一过程中,即过了时间τ后,90°脉冲将部份弛豫的磁化矢量M_τ旋转到X(?)Y平面中,并在接收线圈中感应出FID信号。如果τ很短,M_τ还是负的(M_τ<0),90°脉冲(?)_1,作用后M_τ沿X向负Y轴旋转(图20c),     

~(13)C核磁共振(三)

8.1 通过一个键的C与H偶合除了化学位移之外,C—H的偶合常数也能提供重要的信息,测量J值时必须取不去偶或用交替脉冲双共振方法。这两种方法都需时较长,并且要求样品量较多。~1J_(CH)也可从~1H谱的~(13)C卫星线测得。 ~1J_(CH)在120-130Hz之间~2J(CH)、~3J(CH)~4J(CH)都小于     

~(13)C核磁共振(一)

自从物理学家发现核磁共振(NMR)有化学位移,从而使NMR进入了有机化学实验室,到现在已有三十年了。早期,最常见的是高分辨~1H谱。70年代以后,由于引入了PFT技术,NMR灵敏度低的困难已经解决了,因此,测定低丰度核的工作受到广泛重视,其中最重要的是~(13)C。自从有了PFT的商品仪器,~(13)C NMR工作蓬勃开展,文献急剧增加,可以认为:~(13)C与~1H NMR相辅相成,是目前有机化学家手中最强有力的武器。我国建立NMR技术已有十多年的历史,~(13)C方面也有了不少工作。到目前为止,介绍~(13)C谱基础知识的资料还十分少,为此,我们编译了德同化学家von E.Breitmaier及G.Bauer所著的《~(13)C NMR Spektroskopie》一书,并选译部分练习题,以供有机化学工作者参考。本文将以连载方式在本刊载出。限于编译者的水平,错误难免,请批评指正。     

~(13)C核磁共振(二)

4.识别图谱的化学方法 4.1 氘代用化学方法将样品中的某些位置上的氢以重氢(~2D)代替之后,与这个氢键接的~(13)C共振峰就发生相应变化,利用这种变化可以识别谱峰。~2D的I=1,因此,CD,CD_2,CD_3的碳顺次表现为三重峰(1:1:1),五重峰(1:3:5:3:1)及七重峰(1:3:5:7:5:3:1),又由于~2D有四极弛豫作用,使~(13)C讯号加宽,这两重原     

Overlapping resonances interference-induced transparency: The S(0) → S(2)∕S(1) photoexcitation spectrum of pyrazine

The phenomenon of "overlapping resonances interference-induced transparency" (ORIT) is introduced and studied in detail for the S(0) → S(2)∕S(1) photoexcitation of cold pyrazine (C(4)H(4)N(2)). In ORIT, a molecule becomes transparent at specific wavelengths due to interferences between envelopes of spectral lines displaying overlapping resonances. An example is the S(2)???S(1) internal conversion in pyrazine where destructive interference between overlapping resonances causes the S(0) → S(2)∕S(1) light absorption to disappear at certain wavelengths. ORIT may be of practical importance in multi-component mixtures where it would allow for the selective excitation of some molecules in preference to others. Interference-induced cross section enhancement is also shown.     

The crystal structures of chiral (R/S) (C8H11N)2·Cu(OAc)2

The two title chiral complexes (R/S) (C₈H₁₁N)₂·Cu(OAc)₂ were synthesized by the reaction of chiral d(+)/l(?)-??-ethylphenyl amine with copper(II) acetate monohydrate in dry ethanol. The crystal structures of 1a and 1b were obtained and determined by X-ray crystallography.     

Regioselective copper(I)-catalyzed C–H hydroxylation/C–S coupling: expedient construction of 2-(styrylthio)phenols

Regioselective copper(I)-catalyzed C–H hydroxylation/C–S coupling of aryl thiols with vinyl halides was developed. Starting from substituted aryl thiols and vinyl halides, various 2-(styrylthio)phenol derivatives were efficiently prepared. The application of the synthetic methodology to generate the bioactive organic intermediate was also exemplified.