氮化硼固相转变的船形模型

 船形转变模型是有rBN结构向wBN结构的固相转变模型。在静高压下，相比于以椅形方式，rBN更容易以船形方式转变。     

Theoretical investigation of 1,4-dioxane complexes with water in the <Emphasis Type="Italic">chair</Emphasis> conformation by semiempiric MNDO/PM3 method

The structure and relative stability of 1,4-dioxane-water, (Diox)_n·(H₂O )_m (n = 1, 2, m = 1–6), molecular complexes have been calculated by semiempirical MNDO/PM3 method. A considerable variety of (Diox)_n·(H₂O )_m isomeric structures was stated. The mean energy of O_Diox…H_W-O_W hydrogen bond in (Diox)_n·(H₂O)_m complexes formed by 1,4-dioxane molecules in the chair conformation amounts to ?2.293 ± 0.210 kcal/mol with the average bond length 2.797 0.015 Å.     

用左手手势巧学常见单糖的结构式*

分享了一种巧用左手手势,结合一首五言口诀快速判断糖分子结构的方法。口诀为:“罗卓葡古塔,甘露艾半乳。核阿木来苏,酮糖果山古”,包含了常见的12种醛糖和6种酮糖。通过该方法,不仅能快速准确写出各种常见糖的Fischer投影式,而且还可应用于糖分子相应的Haworth透视式及椅式构象,值得在糖类教学中进行推广。     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.     

Cover Picture: Controlling the Chair Conformation of a Mannopyranose in a Large‐Amplitude [2]Rotaxane Molecular Machine (Chem. Eur. J. 21/2009)

A domino effect from one extremity to the other is observed in a large‐amplitude mannosyl [2]rotaxane molecular machine. In their Communication on page 5186 ff., F. Coutrot and E. Busseron describe the efficient preparation of new [2]rotaxane molecular machines containing anilinium and either mono‐ or disubstituted pyridinium amide stations. In the case of the disubstituted pyridinium amide, the macrocycle shuttles from the anilinium to the pyridinium upon deprotonation and causes an impressive flipping of the chair conformation of the glucidic moiety.

     

Controlling the Chair Conformation of a Mannopyranose in a Large‐Amplitude [2]Rotaxane Molecular Machine

Molecular machines boarding now! Molecular machines containing dibenzo[24]crown‐8 (DB24C8) and based on an anilinium and a pyridinium amide station have been prepared. The DB24C8 shuttles upon variation of pH and interacts differently with the pyridinium amide station depending on its substitution. When the DB24C8 sits around the disubstituted amide, the conformation of the pyranose changes from ¹C₄ to ⁴C₁.

     

Structural and Thermal Characterisation of Nadimide Resins

A series of hexachloronadimides containing phosphine oxide in the backbone were synthesized by the reaction of bis(3-amino phenyl) methyl phosphine oxide (BAP) with pyromellitic dianhydride (PMDA)/3,3’,4,4’-benzophenone tetracarboxylic acid dianhydride (BTDA)/2,2-bis(3,4-dicarboxy phenyl) hexafluoropropane dianhydride (6F) and hexachloronadic anhydride in glacial acetic acid/acetone. Structural characterisation of the resins was carried out by infrared, nuclear magnetic resonance spectroscopy and elemental analysis. Thermal characterisation of uncured resin was done by differential scanning calorimetry and thermogravimetric analysis. The decomposition temperature of uncured resins were above 310±10°C with T _max 330±10°C in nitrogen atmosphere. Char yield at 800°C ranged from 37–42%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Achievement of ring inversion of myo-inositol derivatives due to silyloxy/silyloxy repulsion enhanced by the trans-substituents on both sides

The introduction of quite bulky trialkyl or diarylalkylsilyl groups into vicinal trans-hydroxy groups induced a conformational flip of certain multifunctionalized cyclohexane rings from the usual chair form possessing more equatorial substituents (equatorial-rich chair form) into another chair-form that has more axial substituents (axial-rich chair form). This realization was experimentally revealed by the conformational study of the synthetic myo-inositol derivatives possessing two tert-butyldimethylsilyl (TBS), two triisopropylsilyl (TIPS), or two tert-butyldiphenylsilyl (TBDPS) groups on an adjacent trans-diol. Among them, the cyclohexane rings of the 4,5-bis-O-TIPS-myo-inositol, 4,5-bis-O-TBDPS-myo-inositol, and 1,2,3,6-tetra-O-benzyl-4,5-bis-O-TBDPS-myo-inositol were in the axial-rich chair form. Comparison of the ring conformations also revealed that the order of the repulsion was OTBDPS/OTBDPS>OTIPS/OTIPS>OTBS/OTBS, and the silyloxy/silyloxy repulsion was enhanced when the two silyloxy groups were placed in the center of the contiguous four equatorial substituents.     

高效手性膦配体的合成及应用

较为详细地综述了高效、应用广泛的手性膦配体的合成进展，并介绍了其在不对称催化反应中的应用。参考文献49篇。     

Butterfly and chair clusters using N,O-chelating ligands: A combined crystallographic and mass spectrometric study

The organic ligand (1-methyl-1H-benzo[d]imidazol-2-yl)methanol (HL¹) was used to react with Cu(ClO₄)₂·6H₂O and triethylamine at 80°C to afford the complex [Cu₄(L¹)₆]·(ClO₄)₂·CH₃CN ( 1 ). Every four-coordinated Cu(II) ion is surrounded with NO₃ coordinated environment, and every five-coordinated Cu(II) ion is surrounded with N₂O₃ coordinated environment. Changing the metal salt to Zn(NO₃)₂·6H₂O, and after adding CH₃COONa, afforded the complex [Zn₄(L¹)₄(NO₃)₂(CH₃COO)₂] ( 2 ), in which every five-coordinated Zn(II) ion is surrounded with NO₄ coordinated environment. High-resolution electrospray ionization mass spectrometry results revealed that complex 1 broke into the most stable fragment [Cu₂(L¹)₃]⁺, and it also can assemble high nuclear peaks in solution. For complex 2 , it was found that the complex exhibited different component distribution in solution. Not only were there substitutions between coordinated anions, but the high nuclear peaks could also be detected.