巯基乙酰萘胺极谱行为研究及分析应用——Ⅰ、疏基乙酰萘胺极谱行为和电极反应机理

巯基乙酰萘胺(简称巯萘剂)在碱性(pH11.6)介质中,于-0.72V(对SCE)处有一灵敏、对称示波极谱(导数)波。用各种极谱、伏安技术及紫外吸收光谱等手段,详细研究了巯萘剂的极谱行为,伏安特性。文中求算了电子转移数(n)、电极表面吸附量(Γ*),探讨了电极反应机理。     

Excited-state kinetics of azoalkanes some further studies with azoethane,azo-n-propane,and azoisopropane

The photochemistry of azo-n-propane is investigated at 366 nm up to 1 atm pressure, and over a range of temperature from 50 to 190°C. Some additional experiments with azoethane at room temperature and azoisopropane at 180 and 190°C are also reported. From a consideration of the pressure dependence of the quantum yields for photodissociation a generalized mechanism is proposed which accounts for the known experimental observations in acyclic azoalkane photochemistry. These observations include the extensive photoisomerization data which were previously obtained for azoisopropane. In the mechanistic scheme dissociation at low pressures is believed to occur mainly from S and T, the vibrationally excited and randomized first excited singlet and triplet states. At high pressures and low temperatures (≤100°C) the major dissociation channel is probably a nonrandom S₁ state. In direct or singlet sensitized photolysis isomerization occurs predominatly at high pressure and is postulated to occur by internal conversion from S, the thermalized singlet, to the ground state. During the process partitioning to the cis or trans isomer is equally probable. In triplet sensitized photolysis isomerization occurs via intersystem crossing from T₁to the ground state. At elevated temperatures (>150°C) dissociation from S, which has a significant activation energy, can compete with return to the ground state.     

Kinetics of the thermal decomposition of ferrocenyl azide: Character of ferrocenyl nitrene

The Arrhenius parameters for the thermal decomposition of ferrocenyl azide in isooctane are A = (5.1 ± 1.4) × 10¹² s^?1 and E_act = 113.1 ± 0.9 (kJ mol^?1) and the rate is relatively insensitive to solvent (isooctane, benzene, acetonitrile: 1:1.7:2.4). The results indicate a relatively nonpolar transition state which is considerably “tighter” than for a normal bond fission reaction. The Arrhenius parameters are comparable to those for aromatic azides and do not offer any support for anchimeric assistance by the iron atom. A kinetic scheme is presented which accounts for the observed products: Nitrogen, ferrocene, aminoferrocene, azoferrocene, and insoluble material. Rates of hydrogen abstraction by the intermediate ferrocenyl nitrene from cyclohexane, benzene, and acetonitrile are used to show that the nitrene is nucleophilic. © 1994 John Wiley & Sons, Inc.     

Near-field scanning optical microscopy of single molecules by femtosecond two-photon excitation

We present a demonstration of near-field scanning optical microscopy of single molecules based on ultrafast two-photon-induced fluorescence. Measurements were performed by use of 100-fs pulses at 800 nm from a Ti:sapphire laser to excite the two-photon transition in Rhodamine B molecules. Although near-field probes are normally metal coated to achieve superresolution, we used uncoated tips to achieve sufficiently high optical powers to generate acceptable fluorescence emission rates. Images of single molecules demonstrate a resolution of ~175nm(< lambda/4) on a topographically smooth surface, which surpasses the apparent lambda/2 resolution limit for uncoated tips operating in the linear response regime.     

Heterocyclic tautomerism. XI. Structures of 5,5′-bitetrazole and 1-methyl-5-(2′-pyridyl)tetrazole at 130 K

The X-ray crystal structures of 5,5-bitetrazole and 1-methyl-5-(2-pyridyl)tetrazole at 130 K are described. 5,5-Bitetrazole exists as the 1 H, 1'H-tautomer and packs in chains held together by pairs of intermolecular hydrogen bonds. It crystallizes in the monoclinic space group P2₁/n witha=4.945(1),b=6.367(1),c=8.491(1) Å and =99.233(7)^o. In 1-methyl-5-(2-pyridyl)tetrazole the two heterocyclic rings are nearly coplanar and the molecular packing is controlled by intermolecular – interactions. It crystallizes in the triclinic space group P1 witha=6.667(1),b=7.135(1),c=9.202(1)Å, =89.59(1), =69.08(1), and =66.62(1)^o.     

Convenient preparation of tert-butyl beta-(protected amino)esters

Refluxing an aldehyde 1 with benzotriazole and benzylcarbamate in the presence of a catalytic amount of p-TsOH gave the corresponding benzyloxycarbonylamino-1-(1-benzotriazolyl)alkane 2 in good yields. Compounds 2 treated with substituted tert-butyl acetates 3 using LDA as a base afford smoothly and under mild conditions the N-2-protected 3-aminoalkanoic esters 4.     

beta-acylvinyl anion and dianion equivalents: lithiation of 1-[(2EZ)-3-chloroprop-2-enyl]-1H-1,2,3-benzotriazole: preparation and elaboration of 1-(2-oxiranylvinyl)-1H-benzotriazoles

The allyllithium generated from 1-[(2EZ)-3-chloroprop-2-enyl]-1H-1,2,3-benzotriazole (5) and LDA, in the presence of HMPA, reacts with enolizable and nonenolizable carbonyls solely at the CCl terminus to give 1-(2-oxiranylvinyl)benzotriazoles 6a-g in 61-82% yields. Allyllithiums generated from 6a,c reacted exclusively at the CBt terminus to give 10a-d in 68-88% yields. Acidic hydrolysis of (oxiranylvinyl)benzotriazoles 6a-g and 10a-d provided 4-hydroxyalk-2-en-1-one derivatives 12a,b,c,e,g, 13a-d, and furan 14 in 54-86% yields.