4S,3d,后面呢?

在教电子构型一节时,学生们往往感到难于记住轨道的填充次序,许多教科书(也有不少教师)对此也没有给出有效的解决办法。本文介绍一个简便实用的方法,将有助于对这一问题的学习和记忆。做法如下: 1.画一张7×7的方格子图。2.在对角线上算出已知的各S轨道。     

d–d Dative Bonding Between Iron and the Alkaline-Earth Metals Calcium,Strontium, and Barium

Double deprotonation of the diamine 1,1′-(tBuCH₂NH)-ferrocene ( 1 -H₂) by alkaline-earth (Ae) or Eu^II metal reagents gave the complexes 1 -Ae (Ae=Mg, Ca, Sr, Ba) and 1 -Eu. 1 -Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe⋅⋅⋅Mg distance in 1 -Mg is too long for a bonding interaction, but short Fe⋅⋅⋅Ae distances in 1 -Ca, 1 -Sr, and 1 -Ba clearly support intramolecular Fe⋅⋅⋅Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related ¹H NMR chemical-shift difference between the Cp α and β protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe→Ae dative bonding. A comprehensive bonding analysis of all 1 -Ae complexes shows that the heavier species 1 -Ca, 1 -Sr, and 1 -Ba possess genuine Fe→Ae bonds which involve vacant d-orbitals of the alkaline-earth atoms and partially filled d-orbitals on Fe. In 1 -Mg, a weak Fe→Mg donation into vacant p-orbitals of the Mg atom is observed.     

A new facile synthesis of d₄-pterosin B and d₄-bromopterosin, deuterated analogues of ptaquiloside

Ptaquiloside (Pta) is a potent carcinogen present in bracken fern and in soil matrices, that can potentially leach to the aquatic environment. More recently its presence in the milk of different farm animals has been reported. Pterosin B (Ptb) and bromopterosin (BrPt) represent the most convenient analogues in the detection of ptaquiloside by mass spectrometry. Pterosin sesquiterpenes are also involved in many patented biomedical protocols. In this work we introduce a new and convenient approach to the synthesis in three steps and more than 80% yield of d?-pterosin B (d?-Ptb) and d?-bromopterosin (d?-BrPt), useful as internal standards in the quantification of ptaquiloside.     

Synthesis of Novel Classes of Pyrido[2,3‐d]‐pyrimidines,Pyrano[2,3‐d]pyrimidines,and Pteridines

6‐Amino‐5‐formyluracils 1 and 5‐formyl‐6‐hydroxyuracils 4 react with Meldrum's acid 2 in the presence of piperidine as catalyst under thermolytic conditions to afford 6‐carboxy‐2,4,7‐trioxopyrido[2,3‐d]pyrimidines 3 and 6‐carboxy‐2,4,7‐trioxopyrano[2,3‐d]pyrimidines 5 in good yield. Under identical conditions, 6‐amino‐5‐nitrosouracils 6 react with 2 to afford pteridine‐6‐carboxylic acids 7 in good yields.     

Synthesis of d,l-α-Tocopherol Catalyzed by Heteropoly Acids

d,l-a-Tocopherol(vitaminE)isgenerallysynthesizedbycondensingtrimethylhydroquinone(TMHQ)withphytolorisophytolcatatyzedbyvariousBronstedandLex'llisacidssuchasZnCI,-HCI'andAICI;'.Anessentialdisadvantageofthesecatalystsistheirhighconsumption.TheratioofZnCI,toTMHQIsaboLltI(I.Futhertllore.thecatalystsaredifficulttoberecoveredandreused.Recentl}.I.V.Rozhevnikovandco-workers'reportedthatthereactioncouldbecatalyzedbyheteropolyacids(HPA)H:PW,=O.,andH;SiW,=O..,.TheconsumptionoftheseHPAw…     

Intramolecular d10–d10 interactions in neutral,dinuclear Au(I) complexes supported by amino-thiazoline- and -thiazole-based P,N-phosphine ligands

The ligands N-(diphenylphosphino)-thiazoline-2-amine (1), N-(diphenylphosphino)thiazol-2-amine (2) and N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine 3, readily reacted with [AuCl(THT)] in dichloromethane to form the linearly coordinated complexes [AuCl(1-κP)] (5), [AuCl(2-κP)] (6) and [AuCl(3-κP)] (7), respectively. Facile deprotonation with t-BuOK or Na₂CO₃ of 5–7 afforded the stable, neutral dinuclear complexes [AuCl(1_—H-κP,κN)]₂ (8), [AuCl(2_—H-κP,κN)]₂ (9) and [AuCl(3_—H-κP,κN)]₂ (10), respectively. The crystal structures of the mononuclear complexes 5, 6 and 7 and of the dinuclear complexes 8, 9 and 10 have been determined by X-ray diffraction. The latter represent rare examples of neutral complexes supported by bridging P,N-ligands which display intramolecular Au(I)···Au(I) d¹⁰–d¹⁰ interactions, in the range 2.8592(4)–2.8831(4) Å.     

Le calcul du déplacement chimique,un outil de validation des structures d’acides nucléiques

The large majority of analytical NMR methods in chemistry or biochemistry are based on the quality of the chemical shift dispersion. The purpose of this work is to show that theoretical chemical shift back calculation starting from structures can be used to select molecular modeling structures in order to differentiate several conformational possibilities. Here we report the result of the chemical shift calculation carried out on two original structures corresponding to two DNA ‘kissing complexes’. The 46 nucleotides sequence corresponds to the RNA deoxyribose analogous implied in the HIV-1_Lai dimerization process. It is interesting to note that, even in cases we are very far from the classical helical structure (loop–loop interaction, AA base pairing, base stacking, misappariement...), the theoretical chemical shift is in very good agreement with the experimental chemical shift (±0.25 ppm). The satisfactory results obtained enable us to conclude that the comparison of the proton chemical shifts is an invaluable tool making it possible to select or to validate oligonucleotides structures.     

mezo-和d, l-2, 3-二氯丁烷气态生成焓的测定

本文用直接量热法测量了298.15K时meso-和d, l-2, 3-二氯丁烷的液态蒸发焓值以及其混合物的液态燃烧焓值, 得到了它们的标准气态生成焓值, 考察了二氯烷烃分子内氯原子间的相互影响和相互作用对其气态生成焓值的影响。     

Condensed aromatics—XXIII. Cyclo[d.e.d.e.d.e.d.e.d.e.d.e]dodecakisbenzene (kekulene)

Some topological properties of coronoids are given. These systems have chemical counterparts in cycloarenes. For one of these molecules, viz. C₄₈H₂₄ kekulene, the simple Hückel molecular orbital analysis has been performed and employed in the construction of a harmonic force field. Finally the set of calculated vibrational frequencies is reported.     

Metalmetal bonding trends in mixed-group,face-shared d3d3 bioctahedral dimer systems,M′M″Cl9 n−

The results of density functional theory (DFT) calculations on a set of binuclear nonachloride complexes M′M″Cl₉ ⁴⁻ (M′=V, Nb, Ta; M″=Cr, Mo, W) and M′M″Cl₉ ²⁻ (M′=Cr, Mo, W; M″=Mn, Tc, Re), in which each metal possesses a nominal d³ valence electronic configuration, are reported. When compared with previous studies on same-group dimers (typified by the M′M″Cl₉ ³⁻ complexes of the chromium triad), the present results display an increased tendency for electron donation from M′ to M″. Structural trends evident for the M′M″Cl₉ ⁴⁻ and M′M″Cl₉ ²⁻ series of dimers are remarkably consistent: weak ferromagnetic coupling between M′ and M″ is the most favorable intermetallic interaction when M″ is a first-row transition metal, antiferromagnetic coupling dominates when M′ is first-row but M″ is second- or third-row, and metalmetal triple bond formation generally yields the lowest-energy structure when neither metal is first-row. These structural trends, and other characteristics of the dimers described here, can be satisfactorily rationalized in terms of the tendency for electron transfer from M′ to M″, coupled with effects due to spin polarization and ligand field splitting of the valence d orbitals on M′ and M″.     

A series of 3d–4f heterometallic MOFs: syntheses,structures, optical,and electrochemical properties

Abstract

A series of heterometallic metal-organic frameworks (MOFs) employing pyridine-2,6-dicarboxylate and 1,10-phenanthroline as ligands have been synthesized hydrothermally. In isostructural compounds 1–3 [Ln(pydc)₃Cu₂(phen)₄]·I·× H₂O (Ln?=?La (1), Nd (2), Dy (3); x?=?6, 5, 5), the metalloligand [Ln(pydc)₃] assembles with [Cu(phen)₂] units to construct a dodecanuclear cluster via Cu–O bonds and π–π interactions. The clusters are further stacked into three-dimensional supramolecular frameworks with nano-sized cavities. In [La(Hpydc)(pydc)₂Zn(phen)₃]·3H₂O (4), the metalloligand [Ln(Hpydc)(pydc)₂] assembles with [Zn(phen)₃] units to construct a tetranuclear cluster via electrostatic interaction and π–π interaction. This work reveals that the changes of lanthanide metalloligands and the coordination pattern of 3d transition centers would result in significant variation in the final structures. The thermal, optical, and electrochemical properties have been well investigated.     

Synthesis,Crystal Structure and Characterization of 3d–4d–4f Heterometallic Clusters Based on Super Tetrahedron Anions

Five heterometallic complexes were prepared in aqueous solution at 3–5 °C and characterized by elemental analyses, inductively coupled plasma analysis, IR spectra, UV–Vis spectra, powder X-ray diffraction and X-ray single-crystal diffraction. Complex 1–5 all contain 4d–4f super tetrahedron cluster anions, which are constructed by Ln^III ions (Ln = Nd^III, Pr^III), [MoO₄]^2? and [Mo₇O₂₄]^6? anions. Differences among 1–5 lie on the assembly of super tetrahedron anions by excess Ln^III and TM^II (TM = Co^II, Ni^II, Cu^II or Zn^II), which generates bigger cluster anions (complex 1–4) or anions with 1D infinite structure (complex 5). The assemble styles for synthons mentioned above show with capped style, head-to-head linking style or side-by-side linking style.     

Addition de cyano-2 aziridines,ylures dázomethine potentiels aux isocyanates

The addition of azomethine ylids resulting from the thermal ring opening of the corresponding 2-cyanoaziridines on methyl and phenyl isocyanates occured exclusively at the CN double bond. Only one orientation of the addition was observed and a mixture or diastereoisomeric imidazolidones was obtained in each case. On the basis of X ray structure of one diastereoisomer the stereochemistry of the other imidazolidones was established by NMR considering the long range coupling constants values between H₂ and H₅ (J_cis < J_trans). The reaction of sodium methylate with the imidazolones led to imidates resulting from a nucleophilic addition on the nitrile fonction on the C₂ carbon atom of the heterocycles. These irnidates are easily hydrolyzed to the corresponding esters. If the reaction was carried out in the presence of oxygen the CHCN group was transformed into CO group via the oxidation of the C₂ carbanion.     

ChemInform Abstract: Ligand Dependence of Metal—Metal Bonding in the d3d3 Dimers M2X9n- (MIII: Cr,Mo, W; MIV: Mn,Tc, Re; X: F,Cl, Br,I)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

syn,Anti isomerization of 5,5′-Bis-5H-dibenzo[a,d]cyclohepten-5-ylidene

syn-5,5-Bis-5H-dibenzo[a,d]cyclohepten-5-ylidene (2syn), an overcrowded bistricyclic aromatic ene with central seven-membered rings, undergoes a thermal isomerization to the anti stereoisomer (2anti) at elevated temperatures, with G _inv (174°C)=36.4 kcal/mole. The high-energy barrier for syn anti isomerization of2 is compared with the corresponding inversion barrier of 5H-dibenzo[a,d]cycloheptene derivatives and interpreted in terms of a lower degree of overcrowding in2 relative to bistricyclic enes (1) with central five- and six-membered rings. The overcrowding features of2syn,2anti, and theiranti-10,11,10,11-tetrahydro derivative (3) is analyzed, and a mechanism for the syn anti isomerization of 2 is proposed.     

Three-dimensional 3d-4d Heterometallic Coordination Polymer——Synthesis,Structure,Magnetic and Luminescent Properties

A new three-dimensional 3d-4d heterometallic coordination polymer,[Cd2Mn(H2O)4(BTC)2]·2H2O(BTC=1,3,5-benzenetricarboxylate) was prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction.This compound crystallized in the monoclinic space group C2/c,with cell parameters a=1.9452(4) nm,b=0.7094(2) nm,c=1.8064(4) nm,β=118.02(3)°,V=2.2004(8) nm3 and Z=4.Its structure contains trinuclear mixed metal clusters,which are further connected by BTC to form a three-dimensional framework.The compound exhibits intense photoluminescence at room temperature.Magnetic studies of the compound show a dominant antiferromagnetic exchange between the Mn(Ⅱ) ions.     

Optimisation d’une sélection in vitro d’enzymes

Optimisation of an in vitro enzyme selection. Isolation of a catalyst for a given chemical reaction may be achieved by in vitro selection of enzymes from a protein library. Here, we investigate the polymerisation reaction on filamentous phage and the cross-linking of substrate on phage to optimise an in vitro selection for DNA polymerase activity. The efficiency of the optimised selection is measured by enrichment factors up to 3.8 × 10³, the highest described so far for an in vitro selection of proteins for catalysis. It should be useful for directed polymerase evolution towards novel catalytic activities. To cite this article: E. Orsi, J.-L. Jestin, C. R. Chimie 6 (2003).