极性转换概念引入有机化学教学中的尝试

一、问题的提出有机合成反应的一个中心问题是要构成碳—碳键。在构成碳—碳键的反应中,除游离基反应和协同反应外,大部分属于极性反应,亦称路易斯酸碱反应,即带正电荷的碳原子与带负电荷的碳原子相互作用而生成碳—碳键。有机化合物中碳原子所带电荷是由其相连或相邻近的杂原子所决定的。以羰基化合物醛、酮为例,羰基碳原子是带正电荷的,而α-碳原子上     

醛、酮结构对羰基亲核加成反应活性的影响

醛、酮分子中都含有活泼的羰基 ,亲核加成是醛酮最重要、最典型的反应之一。其反应历程为 :式中Ｒ为Ｈ或烃基 ,Ｎｕ为亲核试剂。这两种历程 ,决定反应速率的关键步骤均为Ｎｕ对羰基的进攻[1～ 3 ] 。因此 ,羰基化合物的结构以及Ｎｕ的性质对加成反应进行的难易程度均有影响。但在相同的条件下 ,同一亲核试剂对不同羰基化合物的加成反应 ,影响反应活性的因素就只有羰基化合物的结构了。国内有机化学教科书[3～ 7] 一般都是从两方面论述羰基反应活性的 :①电子因素 :当羰基碳上连有给电性基团 (如烷基、芳基等 )时 ,由于中心碳原子的电正性减…     

芳香酮结构与烯烃加成反应中的区位选择效应的理论研究

研究了芳香酮与烯烃在RuH2(CO)(PPh3)3催化剂催化下发生亲核加成反应生成邻位产物的区位选择效应规律. 采用从头算方法优化得到了12种芳香酮反应物的稳定结构, 研究了共轭效应、电子效应和立体效应对反应活性和选择性的影响, 提出了芳香酮上b位碳原子与羰基在LUMO轨道中形成平面"U弯区"是进行加成反应的必要条件. 在同类骨架结构芳香环上, 相同位置的取代原子不同, b位碳原子的正电荷越大, 生成邻位产物速度越快, 产率相应较高. 当羰基上氧原子与芳香环上邻位碳原子距离达到一定数值, 立体效应占主导位置, 最佳反应距离为0.27~0.30 nm. 同时, 提出芳香酮催化加成反应的可能机理是经过了Ru催化剂与芳香酮上共轭结构的形成, 1, 2氢迁移造成C-H键的断裂而进行的.     

过氧草酸酯结构和取代基对其化学发光的影响

通过单晶测定和理论研究阐述了过氧草酸酯化学发光中取代基的影响.几种典型的芳基草酸酯所观察的化学发光效率随着羰基碳原子的正电荷增加而递增.通过电子密度函数的计算印证了芳基草酸酯对过氧化氢亲核进攻的活泼性.     

过氧草酸酯结构和取代基对其化学发光的影响(英)

通过单晶测定和理论研究阐述了过氧草酸酯化学发光中取代基的影响 .几种典型的芳基草酸酯所 观察的化学发光效率随着羰基碳原子的正电荷增加而递增 .通过电子密度函数的计算印证了芳基草酸酯 对过氧化氢亲核进攻的活泼性 .     

一种判断羧酸衍生物加成—消除反应活性的方法

羧酸衍生物与亲核试剂反应的历程已经研究清楚,首先是亲核试剂进攻羰基碳原子发生亲核加成,然后进行消除,属于加成-消除反应。其活性次序为:RCOX>(RCO)_2O>RCO_2R′>RCONHR′,此活性次序可用电子效应加以解释。由于与羰基直接相连的—(X|¨)、—(O|¨)COR、—(O|¨)R′、—(N|¨)HR′等基团均具有供     

碳正离子重排反应的推动力

碳正离子是指碳原子带有正电荷的物种,它属于一类重要的活性中间体。在烯烃的亲电加成,脂肪族亲核取代(S_N1)、消除(E_1)以及芳香亲电取代等反应中都涉及到这类中间体。碳正离子的重要化学特征之一是容易发生重排。在重排反应中,最常见的方式是分子内的1.2迁移。一般说来碳正离子的重排是通过烷基,芳基或氢带着它的电子对来进行转移,并在基团离去的碳原子上形成一个新的碳正离子。     

羰基衍生物亲水性的研究

羰基衍生物的水解反应和水合反应是按亲核加成机理进行的.所以,羰基碳原子的亲电性对反应的难易起决定作用.一、原子电荷判据文献中常以电子电荷较少作为原子亲电性的度量.如苯环上的亲核取代反应就是这样解释的.对羰基衍生物,我们选取了:甲酰胺、甲醛、甲酰氟及乙烯脲、一硝基乙烯脲、二硝基乙烯脲两个模型分子系列进行讨论.它们的亲水性次序分别是:     

催化分子内α-重氮酯和酮的不对称同系化反应

<正>Angew.Chem.Int.Ed.2015,54,1608~1611路易斯酸催化α-重氮酯和羰基化合物的同系化反应是合成β-酮酸酯化合物的有效方法,反应经历亲核加成、重排历程,其区域选择性复杂,立体选择性控制困难.以醛、环酮以及活化酮等羰基化合物为亲电试剂的不对称催化反应已有成功报道,仅有的一例简单酮与α-重氮酯的反应,在手性双氮氧-钪配合物催化剂条件下得到了α-胺化产物.四川大学化学学院冯小明、李伟等基于他们在这一领域的系统研究,设计了分子内的简单酮与α-重氮酯的不对称同     

对羰基结构的极性与极化性的讨论

共价键的极性和极化性是表征共价键性质的两个物理量,是两个不同的概念。在有机化学教学中,特别是在解释化合物的结构与化学性质的关系方面,都十分重要。然而,笔者发现,一些有机化学教科书在羰基结构这部分内容中,常将两个概念相互混淆,让人读起来似是而非。例如有的教材写道:“由于氧原子的电负性较碳原子大,羰基的π电子云就偏向于氧原子方面,使羰基发生了极化,羰基的碳原子带有部分正电荷,而氧原子带有部分负电荷。”这种认为由     

烷基极化效应与X=O键伸缩振动频率

烷基取代物R’X=0的X=0键伸缩振动频率ν与烷基R的极化效应指数PEI(R)的关系可表示为:ν=a bPEI(R)。研究结果表明,烷基的极化效应使X=0键的伸缩振动频率降低。     

Effect of Alkyl Chain Length of N-Alkyl-N′-(2-benzylphenyl)ureas on Gelation

Urea derivatives that were substituted with a 2-benzylphenyl group and an alkyl group functioned as low molecular weight gelators for various organic solvents and ionic liquids. Urea derivatives with long alkyl chains were effective for the gelation of polar solvents. However, they were not suitable for the gelation of non-polar solvents, whereas urea derivatives with short alkyl chains were effective. Ionic liquids were similar to polar solvents in that urea derivatives with long alkyl chains were the most effective gelators. The physical properties of the formed supramolecular gels were analyzed by dynamic viscoelasticity measurements using a rheometer.     

Selective reduction of the nitro group in the presence of the azoxy group. Synthesis of 2-(alkyl-NNO-azoxy)anilines

Tin(ii) chloride selectively reduces the aromatic nitro group to the amino group, the azoxy group remaining intact. This allows the preparation of 2-(R-NNO-azoxy)anilines from 2-(R-NNO-azoxy)nitrobenzenes bearing electron-donating or weak electron-withdrawing substituents (Me or Br) in the benzene ring and alkyl substituents at the distal N atom of the azoxy group. The presence of electron-withdrawing substituents at the azoxy group (for example, CO₂Et) leads to a change in the direction of the reaction resulting in selective reduction of the azoxy group to the hydrazo group.     

电喷雾质谱法对重烷基苯的族组成分析与结构鉴定

建立了一种系统的分析重烷基苯的方法。通过柱色谱对重烷基苯进行了分离，将其分成了六个族组分，对这六个族组分进行红外、紫外以及荧光鉴定，确定了各族组分的归属，利用电喷雾质谱测定了第二到第五族组分磺酸盐的相对分子量分布，结合红外、紫外所测定的结果，及每族物质的不饱和度和通式，推算出了烷基芳烃部分的相对分子质量和烷基苯的碳数分布。     

烷基的憎水指数

本文提出憎水指数HBI来定量烷基的憎水能力, 结果表明: 烷基的憎水指数能较好地预报有机物在水中的溶解度、在正辛醇/水两相中的分配系数。     

Influence of satellite groups on telechelic antimicrobial functions of polyoxazolines

The antimicrobial activity of poly(alkyloxazoline) telechelics with one quaternary N,N-dimethyldodecylammonium (DDA) end group was found to be greatly controlled by the non-bioactive distal end group, the so-called satellite group. In systematic investigations, the nature of the latter groups was varied to explore the mechanism of the satellite effect. To this end, poly(2-alkyl-1,3-oxazoline)s (alkyl = ethyl, methyl) with a DDA-group at the terminating end and varying alkyl, aminoalkyl, and polyphenyloxazoline block satellite groups, have been synthesized. Poly(oxazoline) derivatives with polydispersity indices of 1.06-1.20 and molecular weights from 2,200 to 12,800 g . mol(-1) could be obtained. The macromolecular structures have been confirmed by NMR spectroscopy and ESI-MS measurements. The polymers were investigated with regard to their antibacterial efficiency towards the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli. It was found that the introduction of alkyl chain satellites of 4-10 carbon atoms in length afforded antimicrobial activity of the polymers against both microbes that was about 2-3 times higher than that of the well-known structurally comparable low molecular weight biocide, dodecyltrimethylammonium chloride (DTAC). Based on the antimicrobial effects of the investigated polymers, a mechanism for the satellite effect was proposed.     

The random contact point model for pair interaction coefficients of unlike solute molecules

The random contact point model described in previous papers is extended to include like-unlike pair interaction coefficients. On the basis of this extension we present the thermodynamics of group interactions involving alkyl, hydroxyl and amide (peptide) groups and water molecules. The values obtained for the Gibbs energy of group interaction (absolute values ranging from 1.5 to 9.8 kJ-mol^–1) indicate that all these groups attract or repel each other in aqueous solutions with comparable strength. Group interaction parameters obtained from aqueous and non-aqueous systems, and based on interaction coefficients and other thermodynamic quantities, agree well. The model also allows for the quantification, though not for the prediction, of the cooperativity of hydrophobic interaction.     

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic C_A* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.     

Poly(L-lactide) macrodiols (HOPLLAOH): Influence of linear alkyl diols as initiators: Synthesis and characterization

A series of α,ω-hydroxy telechelic poly(L-lactide)s (HOPLLAOHs) were synthesized by ring-opening polymerization (ROP) of L-lactide (L-LA) using tin octoate [Sn(Oct)₂] as catalyst and a family of linear alkyl diols as initiators [HO–[CH₂]_m–OH, where m = 2, 4, 6, 8, 10, and 12]. A systematic analysis of these HOPLLAOHs species in terms of their thermal properties was realized by DSC. In this sense, the linear alkyl group had an important influence on the glass transition temperature (T_g); a relatively high content of alkyl group on the HOPLLAOH increased the flexibility of the polyester, evidenced by a value of T_g inversely proportional to the weight percent of the alkyl group. Besides, the alkyl groups had an effect on the crystallization temperature (T_c), melting temperature (T_m), and crystallinity (x_i). Additionally, HOPLLAOHs were characterized by ¹H and ¹³C NMR, FT-IR, MALDI-TOF, and GPC.     

Improvement of stability of phenacyloxycarbamidomethyl (Pocam) group,a cysteine protecting group removable with zinc reduction,under acidic conditions

In order to improve the stability of phenacyloxycarbamidomethyl (Pocam) group, a cysteine protecting group removable with zinc reduction, under acidic conditions, various alkyl substituents on the nitrogen atom of Pocam group were examined. As a result, attachment of an electron-withdrawing group improved the stability, and 2,2,2-trifluoroethyl (Tfe) group was most effective among four substituents tested. Tfe-Pocam group could be used in solid-phase peptide synthesis and peptide condensation reactions, and it was also useful for regioselective disulfide formation reactions.