Conformation and stereodynamics of 1,2-diaryltetrahydropyrimidine and of its five- and seven-membered ring analogs

The 1-(2-nitrophenyl)-2-(2-methylphenyl)-1,4,5,6-tetrahydropyrimidine and its five- and seven-membered ring analogs were synthesized and their conformational properties investigated by low temperature NMR spectroscopy and DFT theoretical calculations. Restricted rotation of the aryl substituents were observed in all cases and the corresponding barriers determined. In the case of the six-membered ring derivative the additional conformers resulting from a ring inversion process were also detected.     

In situ real-time study buckling behavior of boron nitride nanotubes with axial compression by TEM

The real time analysis structure evolution of BNNT with compression showed that the formation of V-shape in the post-buckling before BNNT fracture was reversible.     

Synthesis and spectroscopic analysis of tetraphenylporphyrinatoantimony(V) complexes linked to boron-dipyrrin chromophore on axial ligands

Tetraphenylporphyrinatoantimony(V) complexes, linked to boron-dipyrrin chromophores on axial ligands, were synthesized. The fluorescence spectra of 1a, 1b and 1c (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1a); 6-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]hexyloxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1b); bis{3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo}antimony(V) tetraphenylporphyrin bromide (1c)) were analyzed under the excitations of N,N′-difluorobornyl-5-dipyrrinylphenyl (Bdpy) and tetraphenylporphyrinatoantimony(V) (Sb(TPP)) chromophores. Under the irradiation of Bdpy chromophore, the excitation energy was transferred from Bdpy chromophore to the Sb(TPP) moiety at 0.13–0.40 of the quantum yields, even in a polar solvent. On the other hand, the emission of Sb(TPP) chromophores was quenched by Bdpy chromophores at rate constants of 10⁸–10⁹ s⁻¹, independent of on the solvent polarity. Under the excitation of the Bdpy chromophore of 1d (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(phenyloxo)antimony(V) tetraphenylporphyrin bromide) involving both the Bdpy and the phenoxy chromophores on the axial ligands, the excited singlet state of the Sb(TPP) chromophore generated by the energy transfer from the Bdpy chromophore was quenched by the phenoxy ligand via non-radiative processes involving electron transfer. However, rapid back electron-transfer may occur because no absorption of the anion radical of Sb(TPP) was observed by nanosecond laser photolysis.     

ICP OES Simultaneous Determination of Ca,Cu, Fe,Mg, Mn,Na, and P in Biodiesel by Axial and Radial Inductively Coupled Plasma-Optical Emission Spectrometry

Abstract

A simple and rapid method for the simultaneous determination of seven trace elements in biodiesel by axial and radial view Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) is proposed, in which the sample is emulsified with Triton X-100 and water, and in which yttrium is employed as an internal standard. The better obtained quantification limits (10 s) were by axial view, 0.165, 0.099, 0.033, 0.007, 0.016, 0.132, 0.660 µg g^?1 for Ca, Cu, Fe, Mg, Mn, Na, and P, respectively, based on a sample mass of 1.0 g diluted to a final mass of 10 g in the analytical solution. Calibration was carried out with aqueous standards, thus avoiding the use of frequently instable organic standards. Elemental recoveries were in the range of 90 to 109% for all seven analytes studied, and also the precision of the method was satisfactory (RSD < 8%).     

Improper hydrogen-bonded cyclohexane C-Hax?Yax contacts: experimental evidence from H NMR spectroscopy of suitable axial cyclohexane models

B3LYP/6-31+G(d,p) calculations predicted the presence of improper hydrogen-bonded C-H_ax?Y_ax contacts of different strength in cyclohexane derivatives;¹ it was predicted that the addition of an appropriate bridging fragment X_ax between an axial substituent Y₁ and a cyclohexane carbon would strengthen the improper hydrogen-bonded contact C-H_ax?Y₁ when the X_ax-Y₁ bond vector bisects the cyclohexane ring. To support the theoretical predictions with experimental evidence for this effect, several 2-substituted adamantane analogues with suitable improper H-bonded C-H_ax?O contacts of different strength were synthesized, as models of the corresponding cyclohexane derivatives, and their ¹H NMR spectra were recorded at 298 K. The ¹H NMR signal separation within the cyclohexane ring γ-CH₂s is increased when the B3LYP/6-31+G(d,p)-calculated strength of the H-bonded C-H_ax?O=C_ax contact interaction is increased.     

八乙基金属卟啉的轴向配位反应研究及稳定常数测定

测定了八乙基金属卟啉 (OEP) M中当M=Zn, Cu, FeCl 或 MnCl时在CH2Cl2, N,N-二甲基甲酰胺(DMF), 二甲亚砜(DMSO), 吡啶(Py)等4种不同非水溶剂中的紫外-可见光谱, 探讨了溶剂的性质对八乙基金属卟啉光谱的影响. 结果表明八乙基锌、铁、锰卟啉在CH2Cl2中能够与配位溶剂如DMF, DMSO或pyridine 等发生轴向配位反应生成五配位或六配位的金属卟啉配合物. 用微量光谱滴定法测定了Zn、 Fe、 Mn等金属卟啉和配位溶剂发生轴向配位反应的稳定常数(logK). 讨论了中心金属离子的电负性以及配位溶剂的给电子能力对稳定常数的影响.     

单壁碳纳米管的轴向能带工程

单壁碳纳米管具有优异的电子学特性,是制备新一代高性能集成电路的重要材料.碳纳米管芯片之路存在诸多挑战,包括直径和手性的控制生长方法、金属性和半导体性单壁碳纳米管的分离方法、器件加工与集成方法等.这些课题从本质上讲大多属于化学问题,因此碳纳米管芯片研究为化学家们提供了新的机遇与挑战.过去10年来,我们围绕单壁碳纳米管的轴向能带工程这一研究思路,开展了一系列碳纳米管芯片的基础探索工作,发展了若干有效的单壁碳纳米管局域能带的调控方法,包括温度阶跃生长法、脉冲供料生长法、基底调控法以及形变调控法等.本文系统地阐述了这些局域能带调控方法,为使读者对该领域的研究进展有一个较为全面的了解,文中对其他课题组开展的代表性工作也给予了综述性介绍.     

Enantioselective synthesis of axially chiral 1-(1-naphthyl)isoquinolines and 2-(1-naphthyl)pyridines through sulfoxide ligand coupling reactions

Racemic 1-(1′-isoquinolinyl)-2-naphthalenemethanol rac-12 was prepared through a ligand coupling reaction of racemic 1-(tert-butylsulfinyl)isoquinoline rac-7 with the 1-naphthyl Grignard reagent 10. Resolution of rac-12 was achieved through chromatographic separation of the Noe-lactol derivatives 14 and 15, providing (R)-(−)-12 of >99% ee and (S)-(+)-12 of 90% ee. The ligand coupling reaction of optically enriched sulfoxide (S)-(−)-7 (62% ee) with Grignard reagent 10 furnished rac-12, with the absence of stereoinduction resulting from competing rapid racemisation of the sulfoxide 7. Reaction of optically enriched (S)-(−)-7 with 2-methoxy-1-naphthylmagnesium bromide was also accompanied by racemisation of the sulfoxide 7, and furnished optically active (+)-1-(2′-methoxy-1′-naphthyl)isoquinoline (+)-3b in low enantiomeric purity (14% ee). The absolute configuration of (+)-3b was assigned as R using circular dichroism spectroscopy, correcting an earlier assignment based on the Bijvoet method, but in the absence of heavy atoms. Optically active 2-pyridyl sulfoxides were found not to undergo racemisation analogous to the 1-isoquinolinyl sulfoxide 7, with the ligand coupling reactions of (R)-(+)- and (S)-(−)-2-[(4′-methylphenyl)sulfinyl]-3-methylpyridines, (R)-(+)-17 and (S)-(−)-17, with 2-methoxy-1-naphthylmagnesium bromide providing (−)- and (+)-2-(2′-methoxy-1′-naphthyl)-3-methylpyridines, (−)-18 and (+)-18, in 53 and 60% ee, respectively. The free energy barriers to internal rotation in 3b and 18 have been determined, and the isoquinoline (R)-(−)-12 examined as a ligand in the enantioselectively catalysed addition of diethylzinc to benzaldehyde; (R)-(−)-12 was also converted to (R)-(−)-N,N-dimethyl-1-(1′-isoquinolinyl)-2-naphthalenemethanamine (R)-(−)-19, and this examined as a ligand in the enantioselective Pd-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate.     

Synthesis of new axially dissymmetric ligand with large perfluoroalkyl groups

A new axially dissymmetric ligand with large perfluoroalkyl groups, 2,2′-bis(1-hydroxy-1H-perfluorooctyl)biphenyl (1c), which could not be obtained by the coupling reaction of the aryl bromide using copper powder, was synthesized successfully by the coupling reaction using Ni(COD)₂. This ligand showed much higher asymmetric induction in the reaction of diethylzinc with benzaldehyde than the trifluoromethyl (1a) or pentafluoroethyl (1b) analogues.     

Thermodynamic study of axial coordination reaction of zinc porphyrin with metal Schiff base and imidazole complex

A thermodynamic study is reported for the coordination reaction of ZnT ( m-X)PP derivatives (X = NO2, Cl, OCH3, H or CH3) with various ligands L (L= imidazole (Im), 2-methylimidazole (MeIm), clotrimidazole (CIM), imidazole-4-carboxaldehyde (4-CHOIm), unsymmetrical tetradentate copper Schiff base, CuIm(p-Cl), CuIm(p-Br), and nickel Schiff base, NiIm(p-Cl)), in dichloromethane solvent. Conversion of the four-coordinated ZnT( m-X)PP to the five-coordinated species is followed and isosbestic behavior is exhibited in the region among 450 and 700 run. The reaction of a copper(Ⅱ) or nickel(Ⅱ) imidazolate Schiff base with ZnT(m-X)PP results in the formation of an imidazolate bridged heterobinuclear complex. The stoichiometric number is unity for all axial ligands. The equilibrium constants were determined using the β band of ZnT( m-X)-PP in the 293-308 K range by the method of Rose and Drago. It increases with decrease in temperature, and △H0 < 0, △S0 < 0. The stronger the nucleophilic ability of the axial