Electrophilic and Nucleophilic Addition of Alkanethiols to 2-Vinyloxyethylmethacrylate

Under acid- or base-catalyzed conditions, thiols add regio- and chemos-electively either to vinyloxy or methacrylate group of vinyloxyalkyl-methacrylates to give polyfunctional methacrylates or polyfunctional vinyl ethers, respectively.     

对氯硝基苯吸附在银纳米粒子上的偶联反应

表面增强拉曼光谱(SERS)具有极高的检测灵敏度, 通过检测吸附分子的SERS信号, 可以获得表面吸附分子的结构以及可能发生的反应. 在拉曼激发光源的辐射下, 在碱性溶液中, 银纳米粒子表面吸附的对氯硝基苯(PCNB)的SERS光谱与其固体的常规拉曼光谱相比, 出现异常SERS谱. 通过采用密度泛函理论(DFT)计算, 对PCNB以及可能的偶联产物p,p''-二氯偶氮苯(DCAB)进行理论分析以及谱峰归属, 发现这些异常峰来自其偶联产物DCAB的偶氮C－N＝N－C基团的基频振动.     

Non-catalytic Addition of 1,2,4-Triazole to Nucleophilic and Electrophilic Alkenes

Non-catalytic addition of 1,2,4-triazole to vinyl ethers and esters occurs on heating (65-175°C, 4-20 h) to give Markovnikov adducts (yield 30-100%). Electron-deficient alkenes (acrylonitrile, acrylic acid, 4-phenyl-3-buten-2-one) react with 1,2,4-triazole (78-190°C, 4-20 h) to give anti-Markovnikov adducts in yields of 45-83%.     

Nucleophilic and Electrophilic Additions to Silylated Ketenimines Generated from Imidothioesters.

The reactivity of stable silylated N-phenyl ketenimines towards some nucleophilic (organometallics, alcohols, thiols) and electrophilic reagents (PhSCI) were studied. Imino-coumarines (via tandem nucleophilic-electrophilic additions with Peterson olefination) and new phenylthio- and silyl-substituted ketenimines have been prepared.     

Electrophilic and Nucleophilic Aromatic Substitutions are Mechanistically Similar with Opposite Polarity

Confrontation of the recently formulated general mechanism of nucleophilic substitution in electron-deficient arenes with the well-known mechanism of electrophilic substitution revealed that these fundamental processes are mechanistically identical but proceed according to opposite polarity—an Umpolung relation. In this viewpoint this apparently controversial concept is supported by discussion of a variety of experimental results.     

苯三偶氮衍生物吸附在银溶液上的SERRS谱

In this paper, the SERRS of BATD has been investigated, the effect of pH, concentration and electrolyte on SERRS was discussed and the adsorbed state of BTAD was figured. We suggest that the adsorbed state of BTAD is the bonding of benzotriazol to Ag surface via lone pair electron on the nitrogen. With HCl and ascorbic acid aggregate Ag sol, the dependence of SERRS on BTAD concentration behaves differently. In the former case, the adsorbed state changes, but in the latter it remains the same. Small amount of electrolyte will induce the active sites on the surface, but when it is more than 1×10-2mol﹒L-1, the competent adsorbtion reduces the Raman scattering intensity. Hydrogen ions protonize BTAD to BTAHD and reduce the contribution of lone pair electron on N atom of the conjugated system.     

Nucleophilic and Electrophilic Properties of Carbenes,II. 4-Biphenylyl-4-pyridylcarbene

Flash pyrolysis of 4-biphenylyl-4-pyridyldiazomethane ( 4 gave 7-phenyl-2-azafluorene) 5 , which was also synthesized from 3-mesitoylpyridine in four steps. 4-Biphenylyl-4-pyridyl-[¹³C]-diazomethane ( 9 ) was prepared from isonicotinic [¹³C]-acid chloride in three steps. Flash pyrolysis of 9 established that 4a- and 4b-[¹³C]-7-phenyl-2-azafluorenes are formed in a carbene-carbene rearrangement in which ring expansion of the biphenyl part dominates over that of the pyridine ring. These results support the postulate that carbene-carbene rearrangements are favoured by a nucleophilic interaction between the filled singlet carbene sp² (σ) orbital and the lowest unoccupied molecular orbital (LUMO) of the aromatic ring.     

Photoreduction Behaviors of Micropcroxidase-11 Adsorbed on the Roughened Silver Electrodes

MP-ifisanundecapeptideobtainedfrompepsindigestionofcytochromeC.Itisconsideredamodelforc-typecytochromes.MP-lIretainsaminoacidresidues11-21ofcytochromeC.Amongtheresidues,Cys-14andCys-17arebondedtothehemeCvinylgroupsandHis-18servesasaproximalfifthligandtotheFeatom.ItisconsideredaperoxidasebecauseitSactivityissimilartothatofperoxidasesinseveralways.ItwasreportedthatMP-ifcanundergothequasi-reversibleelectrochemicalreactionatmetalelectrodes.Inthispaper,electrochemicalreactionsandphotoreductio…     

黄曲霉素B1在银团簇表面吸附的表面增强拉曼光谱

采用密度泛函理论(DFT)的B3LYP方法和6-311g(d, p)(C, H, O)/LanL2DZ(Ag)基组, 优化得到黄曲霉素分子AFB₁与Ag小团簇形成的复合物AFB₁-Ag_n (n=2, 4, 6)的稳定结构, 并计算了三种复合物的表面增强拉曼光谱(SERS)和预共振拉曼光谱(SERRS), 与实验结果相一致. 计算结果显示: 三种复合物表面增强拉曼光谱中C＝O伸缩振动模的增强因子约为10²-10³, 是由于极化率改变引起的静化学增强. 根据含时密度泛函理论(TDDFT)方法计算得到的吸收光谱, 分别选择407.5、446.2和411.2 nm作为入射光, 计算三种复合物的共振拉曼光谱, 发现在SERRS光谱中, Ag―O伸缩振动的增强因子达到10⁴量级, 主要是由电荷转移产生的共振增强引起的.     

Inner-Sphere Oxygen Activation Promoting Outer-Sphere Nucleophilic Attack on Olefins

Alkoxylation and hydroxylation reactions of 1,5-cyclooctadiene (cod) in an iridium complex with alcohols and water promoted by the reduction of oxygen to hydrogen peroxide are described. The exo configuration of the OH/OR groups in the products agrees with nucleophilic attack at the external face of the olefin as the key step. The reactions also require the presence of a coordinating protic acid (such as picolinic acid (Hpic)) and involve the participation of a cationic diolefin iridium(III) complex, [Ir(cod)(pic)₂]⁺, which has been isolated. Independently, this cation is also involved in easy alkoxy group exchange reactions, which are very unusual for organic ethers. DFT studies on the mechanism of olefin alkoxylation mediated by oxygen show a low-energy proton-coupled electron-transfer step connecting a superoxide–iridium(II) complex with hydroperoxide–iridium(III) intermediates, rather than peroxide complexes. Accordingly, a more complex reaction, with up to four different products, occurred upon reacting the diolefin–peroxide iridium(III) complex with Hpic. Moreover, such hydroperoxide intermediates are the origin of the regio- and stereoselectivity of the hydroxylation/alkoxylation reactions. If this protocol is applied to the diolefin–rhodium(I) complex [Rh(pic)(cod)], free alkyl ethers ORC₈H₁₁ (R=Me, Et) resulted, and the reaction is enantioselective if a chiral amino acid, such as l -proline, is used instead of Hpic.     

金属四苯基卟啉在氧化银和银胶体上的表面增强拉曼光谱研究(英文)

研究了四苯基卟啉金属配合物 (MTPP ;M =Ag ,Cu ,Pd ,Mg)和游离碱 (H2 TPP)在氧化银和银胶体中的表面增强拉曼光谱 (SERS) .在Ag2 O胶体中MTPP和H2 TPP的SERS谱与其普通拉曼谱明显不同 ,可知吸附分子在Ag2 O胶粒表面发生反应所引起 ,况且产物于 4 6 0nm附近有一强烈吸收 ,可知它含有共扼双吡咯发色团 .在OH- 修饰的银胶上也观察到类似的光谱变化 .     

Reactions of Electrophilic and Nucleophilic Substitution in Flavonoid Series Involving Amino Acids and Their Derivatives

Reactions of catechin and dihydroquercetin flavonoids with amino acids containing primary amino groups have been conducted. Amino acids can be used in both electrophilic substitution (Mannich aminomethylation) and electrophilic substitution (acylation) reactions.     

pH-Dependent Surface-Enhanced Raman Scattering of 8-Hydroxy Quinoline Adsorbed on Silver Hydrosol

Surface-enhanced Raman scattering (SERS) of 8-hydroxy quinoline (HQ) adsorbed on silver hydrosols are compared with the FTIR and normal Raman spectrum in the bulk and in solution. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement has been reported. The excitation profile study also supports the evidence of a charge transfer interaction. The effect of pH variation on the SER band intensity is explained in terms of chemisorption of the molecule on bare and chlorinated silver surfaces. The apparent enhancement factor calculations of the principal Raman bands indicate that in the surface-adsorbed state, an HQ molecule is oriented neither flat nor vertical to the silver surface but is tilted. Copyright 2000 Academic Press.     

Zirconium Borohydride - a Versatile Reducing Agent for the Reduction of Electrophilic and Nucleophilic Substrates

Zirconium borohydride, a potential reducing agent, reduces acids, esters, imines to the corresponding alcohols and secondary amines in good yield at room temperature within two hours. This facile reducing property was taken advantage off in the synthesis of pheromones and some novel chiral precursors for asymmetric synthesis.     

A DFT Study on the Molecular Mechanism of Additions of Electrophilic and Nucleophilic Carbenes to Non-Enolizable Cycloaliphatic Thioketones

The molecular mechanisms of addition of dihalocarbenes and dimethoxycarbene to thioketones derived from 2,2,4,4-tetrmethylcyclobutane-1,3-dione were examined on the basis of the DFT wb97xd/6-311g(d,p)(PCM) calculations. Obtained results demonstrated that the examined processes exhibit polar nature and in the case of electrophilic dichloro-, and dibromocarbenes are initiated by the attack of carbene species onto the sulfur atom of the C=S group. Remarkably, reactions involving more electrophilic carbenes (dichloro-, and dibromocarbene) proceeds via stepwise mechanism involving thiocarbonyl ylide as a transient intermediate. In contrast, analogous reactions with nucleophilic dimethoxycarbene occur via a single step reaction, which can be considered as the [2 + 1] cycloaddition reaction initiated by the attack onto the C=S bond. A computational study showed that difluorocarbene tends to react as a nucleophilic species and resembles rather dimethoxycarbene and not typical dihalocarbene species. Significantly higher reactivity of the thioketone unit in comparison to the ketone group, both present in 3-thioxo-2,2,4,4-tetramthylcyclobutanone molecule, was rationalized in the light of DFT computational study.     

Ag4Fe（CN）6溶胶表面对PABA分子增强机制及吸附态的探讨

通过向对氨基苯甲酸（ＰＡＢＡ）－Ａｇ_４Ｆｅ（ＣＮ）_６溶胶体系分别滴加少量Ｋ_４Ｆｅ（ＣＮ）_６、Ｋ_３Ｆｅ（ＣＮ）_６、Ｎａ_２Ｓ_２Ｏ_３、Ｈ_２Ｏ_２、ＮａＣｌ和ＮａＮＯ_３水溶液，以及改变体系ｐＨ值对ＰＡＢＡＳＥＲＳ谱带影响的观测，探讨Ａｇ_４Ｆｅ（ＣＮ）_６溶胶体系对ＰＡＢＡ分子的增强机制及在胶体表面受到极大增强的分子吸附态。